Tag: Breast Cancer

Reassessing the Role of Carboplatin in Neoadjuvant Therapy for HER2-Positive Breast Cancer: Insights from the neoCARHP Trial

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SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. It is estimated that in the US, approximately 321,910 new cases of female breast cancer will be diagnosed in 2026, and about 42,140 women will die of the disease, largely due to metastatic recurrence.

Human epidermal growth factor receptor 2–positive (HER2+) breast cancer accounts for approximately 15%–20% of all breast malignancies and historically has been associated with aggressive disease biology. Over the past decade, the integration of dual HER2 blockade with Trastuzumab (HERCEPTIN®) and Pertuzumab (PERJETA®) alongside cytotoxic chemotherapy has substantially improved outcomes. In patients with Stage II–III disease, neoadjuvant therapy has become the standard treatment approach, enabling early assessment of treatment response and guiding postoperative therapy.

The combination of a Taxane, Carboplatin, Trastuzumab, and Pertuzumab (TCbHP) is widely endorsed by treatment guidelines as a preferred neoadjuvant regimen. However, the inclusion of Carboplatin, originally incorporated as an anthracycline-sparing strategy to mitigate cardiotoxicity, remains a subject of ongoing debate. While platinum agents may enhance antitumor activity through DNA-damaging mechanisms and potential synergy with HER2-targeted therapy, Carboplatin is also associated with increased hematologic and gastrointestinal toxicities that frequently necessitate dose reductions or treatment interruptions.

Several earlier studies have questioned the incremental benefit of Carboplatin in HER2-positive disease. Trials in both metastatic and early-stage settings have suggested that the addition of platinum compounds may not significantly improve response outcomes, while contributing to higher rates of treatment-related toxicity. At the same time, multiple investigations evaluating chemotherapy de-escalation strategies have demonstrated promising activity with taxane-based regimens combined with dual HER2 blockade alone.

Against this evolving backdrop, the Phase III neoCARHP study sought to determine whether Carboplatin could be safely omitted from neoadjuvant therapy without compromising efficacy.

Study Design and Treatment Approach

The neoCARHP trial was a multicenter, open-label, randomized Phase III noninferiority study, conducted across 15 institutions. The study enrolled women aged 18 years or older with previously untreated Stage II or III HER2-positive invasive breast cancer. Patients with metastatic disease, inflammatory breast cancer, bilateral tumors, or prior systemic therapy for breast cancer were excluded.

Participants were randomly assigned in a 1:1 ratio to receive six cycles of either the standard TCbHP regimen or a Carboplatin-free regimen consisting of a Taxane plus Trastuzumab and Pertuzumab (THP). Taxane selection, including Docetaxel, Paclitaxel, or nab-Paclitaxel, was left to investigator discretion. Importantly, Docetaxel dosing differed between arms, with a higher dose used in the THP arm to maintain treatment intensity in the absence of Carboplatin.

All patients received Trastuzumab and Pertuzumab every three weeks. Surgery was scheduled within six weeks following completion of neoadjuvant therapy. Postoperative treatment followed standard guidelines: patients achieving a pathologic Complete Response (pCR) typically continued Trastuzumab with or without Pertuzumab to complete one year of HER2-targeted therapy, while those with residual disease were eligible to receive adjuvant Trastuzumab emtansine (KADCYLA®).

Between April 2021 and August 2024, 774 patients were randomized, and 766 who received at least one dose of study therapy were included in the efficacy analysis. Baseline characteristics were well balanced between the treatment arms, with most patients presenting with Stage II disease and approximately one-third being node-negative.

The Primary endpoint of the trial was the rate of pathologic Complete Response in the breast and axilla (ypT0/is ypN0) in the modified intention-to-treat population.

Efficacy Outcomes

Pathologic Complete Response was achieved in 64.1% of patients treated with the Carboplatin-free THP regimen compared with 65.9% in the TCbHP group. The absolute difference of –1.8% fell well within the prespecified noninferiority margin, confirming that THP was statistically noninferior to the standard Carboplatin-containing regimen.

Per-protocol analyses yielded nearly identical results, with both treatment groups demonstrating a pCR rate of 68.5%. Importantly, subgroup analyses showed consistent outcomes across clinically relevant populations, including both Hormone Receptor–positive and Hormone Receptor–negative disease. Among patients with Hormone Receptor–negative tumors, pCR rates approached 78% in both treatment arms.

Safety and Tolerability

A key finding of the neoCARHP study was the improved safety profile associated with the Carboplatin-free regimen. Grade 3 or 4 adverse events occurred in 20.7% of patients receiving THP compared with 34.6% in those treated with TCbHP. Serious adverse events were also less frequent in the THP arm (1.3% vs 4.7%).

Hematologic toxicities were notably reduced with Carboplatin omission. Rates of neutropenia and leukopenia were significantly lower in the THP group, and gastrointestinal toxicities such as diarrhea occurred less frequently. Overall toxicity rates were similar between groups, but the majority of events were low grade. No treatment-related deaths were reported.

These findings suggest that eliminating Carboplatin may substantially reduce treatment-related morbidity while preserving efficacy.

Clinical Context and Emerging Evidence

The results of neoCARHP align with a growing body of evidence supporting chemotherapy de-escalation strategies in HER2-positive breast cancer. Multiple prior trials, including NeoSphere, WSG-ADAPT, COMPASS-HER2-pCR, and DAPHNe, have demonstrated that taxane-based regimens combined with dual HER2 blockade can achieve high pCR rates, particularly in Hormone Receptor–negative tumors.

Collectively, these studies suggest that approximately half of patients with Stage II–III HER2-positive breast cancer may achieve pCR after four cycles of THP, with response rates exceeding 60% after six cycles. For patients with Hormone Receptor–negative disease, pCR rates may approach 80%. Importantly, omitting Carboplatin appears to improve tolerability without compromising early efficacy outcomes, raising the possibility that selected patients with low- or intermediate-risk disease may safely receive less intensive chemotherapy.

Future Directions and Biomarker-Guided Treatment

Despite these encouraging results, several important questions remain. Long-term outcomes, including Event-Free Survival, invasive Disease–Free Survival, and Overall Survival, are still maturing in the neoCARHP trial. Because pCR is not universally validated as a surrogate for survival across all breast cancer subtypes, extended follow-up will be critical to confirm the durability of these findings.

Advances in biomarker-driven treatment selection may also play a key role in refining neoadjuvant strategies. Emerging tools such as PET-guided response assessment, genomic assays like HER2DX, and intrinsic subtype classification may help identify patients most likely to benefit from treatment de-escalation while ensuring that higher-risk individuals continue to receive optimal therapy.

Meanwhile, antibody–drug conjugates are rapidly entering the early-stage setting and could further reshape treatment paradigms. Agents such as Trastuzumab deruxtecan (ENHERTU®) are currently being investigated in neoadjuvant and adjuvant trials and may eventually offer additional Carboplatin-free therapeutic options.

Clinical Takeaway

The Phase III neoCARHP trial demonstrates that a neoadjuvant regimen consisting of a taxane combined with Trastuzumab and Pertuzumab achieves pathologic Complete Response rates comparable to the standard TCbHP regimen while significantly reducing high-grade toxicities.

These findings support the potential omission of Carboplatin in selected patients with Stage II–III HER2-positive breast cancer and represent another step toward individualized, toxicity-conscious treatment strategies in early HER2-positive disease.

Neoadjuvant Taxane Plus Trastuzumab and Pertuzumab With or Without Carboplatin in Human Epidermal Growth Factor Receptor 2–Positive Breast Cancer: The Randomized Noninferiority Phase III neoCARHP Trial. Gao H-F, Ye G-L, Lin Y, et al. J Clin Oncol. DOI: 10.1200/JCO-25-02176

TRODELVY® plus KEYTRUDA® in Metastatic Triple Negative Breast Cancer

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SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. It is estimated that in the US, approximately 321,910 new cases of female breast cancer will be diagnosed in 2026, and about 42,140 women will die of the disease, largely due to metastatic recurrence.

The Persistent Therapeutic Gap in Metastatic TNBC

Triple-Negative Breast Cancer (TNBC) which accounts for roughly 10-15% of breast cancers remains one of the most biologically aggressive breast cancer subtypes, defined by the absence of estrogen and progesterone receptor expression and lack of HER2 overexpression. Despite therapeutic advances, metastatic TNBC carries a dismal prognosis, with 5-year relative survival rates near 15%.

Approximately 40% of TNBC tumors express PD-L1 (combined positive score [CPS] ≥10). Based on results from KEYNOTE-355, the combination of Pembrolizumab (KEYTRUDA®) and chemotherapy (Taxane or Gemcitabine–Carboplatin backbone) became the standard first-line regimen for PD-L1–positive metastatic TNBC, improving both Progression-Free Survival (PFS) and Overall Survival (OS), compared with chemotherapy alone.

However, Real-World Data suggest that nearly half of patients with metastatic TNBC do not receive therapy beyond first line due to rapid progression or early mortality. This underscores the importance of maximizing disease control early in the treatment course.

The Rationale for ADC–Immunotherapy Combination

Sacituzumab govitecan (TRODELVY®) is a Trop-2–directed Antibody–Drug Conjugate (ADC) delivering the topoisomerase I inhibitor SN-38 via a hydrolyzable linker. It previously demonstrated significant survival benefit over chemotherapy in heavily pretreated metastatic TNBC (ASCENT), as well as significantly prolonged Progression-Free Survival compared with standard chemotherapy in the first-line treatment of advanced or metastatic TNBC among patients who are not candidates for PD-1/PD-L1 inhibitors (ASCENT-03).

Given the complementary mechanisms of cytotoxic payload delivery and immune checkpoint inhibition, combining Sacituzumab govitecan with Pembrolizumab represents a biologically compelling strategy to deepen and prolong response in earlier lines of therapy.

ASCENT-04/KEYNOTE-D19: Trial Design

ASCENT-04/KEYNOTE-D19 is a global, randomized, open-label Phase 3 trial conducted across 186 sites in 28 countries.

Eligible patients included:

  • Adults with locally advanced unresectable or metastatic TNBC
  • No prior therapy for advanced disease
  • PD-L1–positive tumors (CPS ≥10, centrally confirmed using PD-L1 IHC 22C3 pharmDx assay)

A total of 443 patients were randomized 1:1:

  • Sacituzumab govitecan (10 mg/kg IV days 1 and 8, q21 days) plus Pembrolizumab (200 mg IV q3 weeks)
  • Physician’s choice chemotherapy plus Pembrolizumab

Stratification factors included:

  • Disease status (de novo metastatic vs. early relapse)
  • Geographic region
  • Prior exposure to anti–PD-1/PD-L1 therapy in curative-intent setting

The Primary endpoint was PFS by Blinded Independent Central Review. Secondary endpoints included OS, Objective Response Rate (ORR), Duration of Response (DoR), and Safety.

Efficacy Outcomes

At a median follow-up of 14 months, the study met its Primary endpoint.

  • Median PFS:
    • 11.2 months with Sacituzumab govitecan plus Pembrolizumab
    • 7.8 months with chemotherapy plus Pembrolizumab
  • Hazard Ratio for progression or death: 0.65 (95% CI, 0.51–0.84; P<0.001)

Investigator-assessed PFS results were concordant. The PFS benefit was consistent across predefined subgroups, including patients with liver metastases and those with early relapse (6–12 months after curative-intent therapy). Notably, median PFS approached one year with the ADC–immunotherapy combination, exceeding historical benchmarks from chemo-immunotherapy trials in this setting.

  • ORR:
    • 60% with Sacituzumab govitecan plus Pembrolizumab
    • 53% with chemotherapy plus Pembrolizumab
  • Complete Response rate: 13% vs. 8%
  • Median Duration of Response:
    • 16.5 months vs. 9.2 months

Although formal hypothesis testing was not performed for secondary endpoints, responses with the ADC combination were notably more durable. Importantly, despite a higher-than-expected ORR in the control arm, responses with chemotherapy were less sustained, likely explaining the PFS separation.

OS data remain immature at this analysis (26% event rate), with medians not yet reached in either arm.

Safety and Treatment Adherence

Grade ≥3 adverse events occurred at similar rates in both groups (about 70%). However, treatment discontinuation due to adverse events was substantially lower with the ADC combination (12% vs. 31%). This difference may reflect the nature of toxicities. ADC-associated events such as diarrhea are generally manageable with supportive care, whereas chemotherapy-related toxicities such as neuropathy may be cumulative and less reversible. Adverse events leading to death occurred in 3% of patients in each arm.

Clinical Interpretation

ASCENT-04/KEYNOTE-D19 establishes the first positive Phase 3 data evaluating an ADC combined with immunotherapy in the frontline treatment of PD-L1–positive metastatic TNBC.

The magnitude of PFS benefit (HR 0.65), prolonged response durability, and lower discontinuation rate suggest that Sacituzumab govitecan plus Pembrolizumab may represent an evolution of first-line therapy in this population.

Given that many patients will not reach subsequent lines of treatment, intensifying effective therapy upfront is clinically meaningful. The ADC backbone may offer sustained tumor control beyond what is achievable with chemotherapy-based combinations.

Limitations and Ongoing Questions

Key limitations include:

  • Open-label design
  • Crossover to Sacituzumab govitecan in the control arm
  • Immature OS data
  • Limited representation of patients previously treated with adjuvant immunotherapy

Future analyses will clarify survival impact and optimal sequencing, particularly as additional ADCs enter earlier lines of therapy. Ongoing trials such as ASCENT-05 (NCT05633654) and SASCIA (NCT04595565) are evaluating Sacituzumab govitecan in high-risk early-stage settings, potentially broadening its therapeutic footprint.

Bottom Line for Practice

For patients with previously untreated, PD-L1–positive, locally advanced unresectable or metastatic TNBC, Sacituzumab govitecan plus Pembrolizumab significantly prolongs Progression-Free Survival compared with chemotherapy plus Pembrolizumab, with durable responses and manageable toxicity.

These findings position ADC–immunotherapy combinations as a potential new backbone strategy in frontline TNBC management, pending maturation of Overall Survival data.

Sacituzumab Govitecan plus Pembrolizumab for Advanced Triple-Negative Breast Cancer. Tolaney SM, de Azambuja E, Kalinsky K, et al. for the ASCENT-04/KEYNOTE-D19 Clinical Trial Investigators. N Engl J Med 2026;394:354-366.

Redefining First-Line Maintenance in HR-Positive, HER2-Positive Metastatic Breast Cancer

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SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. It is estimated that in the US, approximately 321,910 new cases of female breast cancer will be diagnosed in 2026, and about 42,140 women will die of the disease, largely due to metastatic recurrence.

Breast cancer remains a biologically heterogeneous disease, with approximately 70% of tumors expressing estrogen receptors (ER) and/or progesterone receptors (PR). Among patients with metastatic disease, Hormone Receptor (HR)–positive, HER2-negative tumors represent the most common subtype. However, 15%–20% of primary breast cancers overexpress HER2, a historically aggressive phenotype. Notably, more than half of HER2-positive tumors also coexpress hormone receptors, creating a biologically distinct subgroup characterized by signaling interplay between the HER2 and estrogen receptor pathways.

For patients with HR-positive, HER2-positive metastatic breast cancer, the current first-line standard consists of induction chemotherapy combined with dual HER2 blockade (Trastuzumab-HERCEPTIN® and Pertuzumab-PERJETA®), followed by maintenance HER2-targeted therapy plus endocrine therapy. While this approach has significantly improved outcomes, resistance remains inevitable for most patients. Preclinical data have consistently demonstrated bidirectional crosstalk between HER2 and ER signaling, as well as persistent activation of the cyclin D1–CDK4/6 axis, which may drive resistance to both endocrine and HER2-directed therapies. These mechanistic insights provided the scientific rationale for evaluating triple pathway inhibition, simultaneous targeting of HER2, ER, and CDK4/6 in this population.

Biological Rationale for CDK4/6 Inhibition

Cyclin-Dependent Kinases 4 and 6 (CDK4/6) regulate orderly progression from the G1 to S phase of the cell cycle through phosphorylation of the retinoblastoma (RB) protein. Aberrant activation of this pathway is implicated in tumor proliferation and therapeutic resistance across multiple breast cancer subtypes, including HER2-positive disease.

Palbociclib (IBRANCE®), an oral selective CDK4/6 inhibitor, suppresses RB phosphorylation and arrests cell-cycle progression. Preclinical HER2-positive models have demonstrated that sustained cyclin D1–CDK4/6 activity contributes to resistance to HER2-targeted therapies, and dual inhibition of CDK4/6 and HER2 has shown synergistic antitumor effects. Early-phase clinical studies further suggested that combining CDK4/6 inhibition with HER2-directed and endocrine therapy was feasible and potentially additive in efficacy. These findings led to the Phase 3 PATINA trial.

The PATINA Trial: Study Design

PATINA was an open-label, randomized Phase 3 study evaluating whether adding Palbociclib to maintenance therapy could extend disease control in patients with HR-positive, HER2-positive metastatic breast cancer.

Eligibility and Treatment Approach

Patients were enrolled after completing 4 to 8 cycles of induction chemotherapy plus HER2-targeted therapy without disease progression. Key eligibility criteria included:

  • HR positivity (≥1% nuclear staining by IHC)
  • HER2 positivity (IHC 3+ or ISH amplification per ASCO/CAP guidelines)
  • No prior systemic therapy for metastatic disease beyond induction
  • A disease-free interval ≥6 months after prior adjuvant HER2 therapy

A total of 518 patients were randomized 1:1:

  • Palbociclib arm (n=261): Maintenance HER2-targeted therapy + endocrine therapy + Palbociclib (125 mg orally, 21 days on/7 days off; dose reductions permitted)
  • Standard arm (n=257): Maintenance HER2-targeted therapy + endocrine therapy

Baseline characteristics were balanced. The median age was 53.4 years; 99% were female; 61.8% were postmenopausal. Importantly, 54.4% had de novo metastatic disease. The Primary endpoint was investigator-assessed Progression-Free Survival (PFS). Secondary endpoints included Objective Response, clinical benefit, safety, and Overall Survival.

Efficacy Outcomes: A Meaningful Extension of Disease Control

At a median follow-up of 53.5 months, the addition of Palbociclib resulted in a statistically and clinically significant improvement in PFS. The median PFS was 44.3 months in the Palbociclib group and 29.1 months in the standard therapy group (HR=0.75; P=0.02). The estimated PFS rates favored the Palbociclib arm over standard therapy at all measured time points and was 84.9% versus 73.2% at 12 months, 65,2% versus 55.3% at 24 months, and 46.5% versus 38.3% at 48 months respectively.

The depth and durability of response were also enhanced:

  • Confirmed response rate: 32.9% vs. 24.8%
  • Complete response rate: 14.3% vs. 11.3%
  • Median duration of confirmed response: 44.9 vs. 30.8 months

Importantly, when the induction phase is included, total first-line disease control in the Palbociclib arm extended beyond four years. Early mortality was uncommon, with 6-month Overall Survival exceeding 99% in both groups, reflecting favorable biology among patients who completed induction therapy.

The control arm’s median PFS of 29 months exceeded initial projections, likely reflecting mandated endocrine therapy use and the exclusion of patients who progressed during induction, factors that enriched the study population for more favorable disease biology.

Safety Profile

The safety findings were consistent with known toxicities of Palbociclib and HER2-targeted therapies. Neutropenia was the predominant toxicity and febrile neutropenia was rare. Grade 3 and Grade 4 adverse events were 79.7% and 10% in the Palbociclib group versus 30.6% and 3.6% in the standard therapy group.

Clinical Implications

The PATINA trial supports a paradigm shift in the maintenance setting for HR-positive, HER2-positive metastatic breast cancer. By targeting HER2, Estrogen Receptor signaling, and CDK4/6-mediated cell-cycle progression concurrently, this strategy addresses key resistance mechanisms.

Achieving a median PFS exceeding 44 months represents a meaningful advance in a disease subtype historically associated with aggressive biology. While antibody–drug conjugates and other potent HER2-directed agents remain appropriate for selected high-risk patients, this chemotherapy-sparing maintenance intensification strategy provides durable disease control in a substantial proportion of patients.

The open-label design and limited racial diversity are important considerations. Additional analyses evaluating patient-reported outcomes, biomarker correlates, and central nervous system outcomes are ongoing and may further refine patient selection.

Conclusion

The addition of Palbociclib to maintenance anti-HER2 and endocrine therapy significantly prolongs Progression-Free Survival in patients with HR-positive, HER2-positive advanced breast cancer, albeit with increased, but manageable, hematologic toxicity. Triple pathway inhibition targeting HER2, estrogen receptor, and CDK4/6 signaling may now represent a compelling first-line maintenance strategy capable of extending disease control beyond four years in appropriately selected patients.

Palbociclib for Hormone-Receptor–Positive, HER2-Positive Advanced Breast Cancer. Metzger O, Mandrekar S, Goel S, et al. N Engl J Med 2026;394:451-462

Reconsidering Menopausal Hormone Therapy in BRCA1/2 Carriers: Emerging Evidence Challenges Longstanding Concerns

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SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. It is estimated that in the US, approximately 321,910 new cases of female breast cancer will be diagnosed in 2026, and about 42,140 women will die of the disease, largely due to metastatic recurrence.

The tumor suppressor genes such as BRCA1 and BRCA2 help repair damaged DNA and thus play an important role in maintaining cellular genetic integrity, failing which these genetic aberrations can result in malignancies. Mutations in BRCA1 and BRCA2 account for about 20 to 25 percent of hereditary breast cancers and about 5 to 10 percent of all breast cancers. These mutations can be inherited from either of the parents and a child has a 50 percent chance of inheriting this mutation, and the deleterious effects of the mutations are seen even when a second copy of the gene in an individual is normal. Women with germline BRCA1 or BRCA2 mutations face markedly elevated lifetime risks of breast cancer, estimated at up to 70%. More than half of these cancers occur before the age of 50, underscoring the importance of informed counseling regarding risk-modifying exposures. 

For much of the latter half of the 20th century, Hormone Replacement Therapy (HRT) was widely prescribed to alleviate menopausal symptoms and protect against long-term complications such as osteoporosis. This practice shifted dramatically in 2002, when the Women’s Health Initiative reported increased risks of cardiovascular events and breast cancer associated with hormone therapy in older, postmenopausal women. In the aftermath, both patients and clinicians largely retreated from Menopausal Hormone Therapy (MHT), and its use declined sharply.

While those findings reshaped care in the general population, their applicability to women with hereditary cancer predisposition, particularly carriers of pathogenic BRCA1 or BRCA2 variants, has remained uncertain. These women face markedly elevated risks of ovarian and fallopian tube cancers and are therefore advised to undergo risk-reducing bilateral salpingo-oophorectomy at relatively young ages. The procedure is effective for cancer prevention but induces abrupt surgical menopause, often decades earlier than natural menopause, with well-documented short- and long-term consequences including vasomotor symptoms, sexual dysfunction, bone loss, and adverse cardiovascular and cognitive effects.

Menopausal Hormone Therapy (MHT) is the most effective intervention for mitigating these outcomes of early menopause. However, concerns that hormone exposure could further increase breast cancer risk in BRCA carriers have led to substantial hesitation, misinformation, and, in many cases, prolonged untreated symptoms. Researchers have emphasized, recommending premenopausal oophorectomy without offering a safe strategy to manage its consequences creates an untenable clinical dilemma.

Study Design: Emulating a Trial in a High-Risk Population

To address this evidence gap, investigators conducted the largest prospective matched analysis to date examining MHT use and breast cancer risk in BRCA1 and BRCA2 carriers. Using data from a longitudinal cohort, the study sought to emulate a randomized clinical trial by carefully matching women who initiated MHT after menopause, predominantly surgical menopause, to those who did not.

Eligible participants had no prior cancer history, no bilateral mastectomy, and had entered menopause. A total of 676 matched pairs were created, matched one-to-one by gene mutation (BRCA1 or BRCA2), year of birth, and age at menopause. Participants ranged in age from 22 to 76 years, with a mean age of 43.8 years. MHT formulations initiated after menopause included estrogen-only therapy, combined estrogen–progestogen therapy, progestogen alone, tibolone, and conjugated equine estrogen plus bazedoxifene. Cox proportional hazards models were used to estimate breast cancer risk.

Results: No Signal of Increased Breast Cancer Risk

After a mean follow-up of 5.6 years from the date of first MHT use, breast cancer incidence was significantly lower among women who used MHT compared with their matched, unexposed counterparts. Incident breast cancer occurred in 12.9% of MHT users versus 18.9% of non-users (P = 0.002).

Notably, estrogen-only therapy was associated with a substantial reduction in breast cancer risk, corresponding to a 63% relative decrease compared with non-users. In contrast, no increased or decreased risk was observed with combined estrogen–progestogen therapy, progestogen monotherapy, or tibolone. Among the 43 women who received conjugated equine estrogen plus bazedoxifene, no breast cancer diagnoses were reported during follow-up, an exploratory finding that warrants further investigation. Importantly, risk estimates were consistent across BRCA1 and BRCA2 carriers, underscoring the relevance of these findings across mutation subtypes.

Clinical Implications

These data provide critical reassurance for clinicians managing young women with hereditary breast and ovarian cancer syndromes. In contrast to earlier studies conducted in the general population, MHT use in BRCA1/2 carriers was not associated with an increased risk of breast cancer, regardless of formulation. Estrogen-only regimens, in particular, appeared protective, although causality cannot be inferred.

While limitations include a relatively modest follow-up duration and small numbers in certain subgroups, this prospective analysis offers the strongest evidence to date supporting the safety of MHT in this high-risk population. The findings reinforce the need for individualized, evidence-based counseling that balances cancer risk reduction with quality-of-life preservation.

Moving Forward

As MHT formulations continue to evolve, ongoing research will be essential to refine risk stratification and optimize menopause management strategies in BRCA mutation carriers. For now, these results support a personalized approach to MHT use in women experiencing surgical or natural menopause after risk-reducing oophorectomy, provided there are no contraindications. For many patients, informed use of MHT may offer not only symptom relief, but also a path toward improved long-term health and wellbeing without compromising breast cancer risk.

GS3-01. Menopausal Hormone Therapy and the Risk of Breast Cancer in Women with a Pathogenic Variant in BRCA1 or BRCA2. Kotsopoulos J, Seca M, Jacek G, et al. Presented at the 2025 San Antonio Breast Cancer Symposium (SABCS; Abstract GS3-01). 

FDA Approves First Line ENHERTU® plus PERJETA® for HER2-Positive Metastatic Breast Cancer

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SUMMARY: The FDA on December 15, 2025, approved ENHERTU® in combination with Pertuzumab for the first-line treatment of adults with unresectable or metastatic HER2-positive (IHC 3+ or ISH+) breast cancer as determined by an FDA-approved test.

Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. It is estimated that in the US, approximately 321,910 new cases of female breast cancer will be diagnosed in 2026, and about 42,140 women will die of the disease, largely due to metastatic recurrence.

The HER or erbB family of receptors consist of HER1, HER2, HER3 and HER4. Approximately 15%-20% of invasive breast cancers overexpress HER2/neu oncogene, which is a negative predictor of outcomes without systemic therapy. Trastuzumab (HERCEPTIN®) is a humanized monoclonal antibody targeting HER2. Trastuzumab binds to subdomain IV of the HER2 extracellular domain and blocks the downstream cell signaling pathways (PI3K-AKT pathway) and induces Antibody Dependent Cellular Cytotoxicity (ADCC). Pertuzumab (PERJETA®) is a recombinant humanized monoclonal antibody that binds to the HER2 at a different epitope of the HER2 extracellular domain (subdomain II) compared to Trastuzumab, and prevents the dimerization of HER2 with HER3 receptor. Pertuzumab stimulates ADCC similar to Trastuzumab. By combining Trastuzumab and Pertuzumab, a more comprehensive blockade of HER2 signaling can be accomplished, as these two agents bind to different HER2 epitopes and may complement each other and improve efficacy.

Trastuzumab deruxtecan (T-DXd) (ENHERTU®) is a next-generation Antibody-Drug Conjugate (ADC) composed of a humanized monoclonal antibody specifically targeting HER2, with the amino acid sequence similar to Trastuzumab, a cleavable tetrapeptide-based linker, and a potent cytotoxic Topoisomerase I inhibitor as the cytotoxic drug (payload). T-DXd has a favorable pharmacokinetic profile and the tetrapeptide-based linker is stable in the plasma and is selectively cleaved by cathepsins that are up-regulated in tumor cells. Unlike  ado-Trastuzumab emtansine, another ADC targeting HER2, T-DXd has a higher drug-to-antibody ratio (8 versus 4), released payload easily crosses the cell membrane with resulting potent cytotoxic effect on neighboring tumor cells regardless of target expression, and the released cytotoxic agent (payload) has a short half-life, thus minimizing systemic exposure.

Background and Clinical Rationale
Trastuzumab deruxtecan (T-DXd) has demonstrated potent antitumor activity in HER2-positive breast cancer across multiple treatment lines. However, prior to the DESTINY-Breast09 study, all approved indications for T-DXd required patients to have received prior systemic therapy in either the metastatic or adjuvant setting. With the longstanding CLEOPATRA regimen, Docetaxel, Trastuzumab, and Pertuzumab (THP) established over a decade ago as the first-line standard of care, the oncology community has been eager to evaluate whether T-DXd could improve frontline outcomes.

Study Design and Patient Population
DESTINY-Breast09 (NCT04784715) is a randomized, global Phase 3 study designed to evaluate the efficacy and safety of first-line T-DXd with or without Pertuzumab, versus Taxane plusTrastuzumab plus Pertuzumab (THP), in patients with HER2-positive advanced/metastatic breast cancer. A total of 1,157 patients were enrolled across 283 sites worldwide. Eligible patients had centrally confirmed HER2-positive disease (IHC 3+ or ISH+), no prior chemotherapy or HER2-targeted therapy in the metastatic setting, and ≤1 prior line of endocrine therapy. Patients were stratified by Hormone Receptor (HR) status, PIK3CA mutation status, and de novo vs recurrent disease, and randomized 1:1:1 to:

  • T-DXd + placebo – N=387
  • T-DXd + Pertuzumab (T-DXd + P) – N=383
  • THP (control arm) – N=387

The interim analysis presented at ASCO 2025 focused on the comparison between T-DXd + P and THP. The T-DXd monotherapy arm remains blinded until the final PFS analysis.

The Primary endpoint was Progression-Free Survival (PFS) by Blinded Independent Central Review (BICR) in the intent-to-treat population. Secondary endpoints included Overall Survival (OS), PFS by investigator (INV), Objective Response Rate (ORR), Duration of Response (DOR), and Safety.

Efficacy Outcomes: Progression-Free Survival and Response
At a median follow-up of 29 months, T-DXd + P demonstrated a statistically significant and clinically meaningful improvement in PFS compared to THP:

  • Median PFS by BICR:
    • T-DXd + P: 40.7 months
    • THP: 26.9 months
    • HR: 0.56; P <0.00001
  • PFS by Investigator Assessment:
    • Median: 40.7 months vs 20.7 months
    • HR: 0.49 (95% CI: 0.39–0.61)
  • Overall Response Rate (ORR):
    • T-DXd + P: 85.1%
    • THP: 78.6%
  • Complete Response Rate:
    • T-DXd + P: 15.1%
    • THP: 8.5%
  • Median Duration of Response:
    • T-DXd + P: 39.2 months
    • THP: 26.4 months

The PFS benefit was consistent across all patient subgroups, including HR status and PIK3CA mutation.

Safety Profile and Adverse Events
The safety profile of T-DXd + P in the frontline setting was consistent with known toxicities of T-DXd, with no new safety signals. Adjudicated drug-related Interstitial Lung Disease/pneumonitis occurred in 12.1% of patients receiving T-DXd + P (mostly grade 1 and 2) in contrast to only 1.0% among patients receiving THP. Other treatment-related toxicities such as nausea, vomiting, and constipation were more common with T-DXd + P, possibly due to longer median treatment exposure (~3.5 years).

Clinical Implications and Emerging Questions
The marked 13.8-month PFS improvement positions T-DXd + P as a strong candidate to replace THP as the first-line standard for HER2-positive advanced metastatic breast cancer. These results mirror the transformative impact of T-DXd seen in the second-line DESTINY-Breast03 trial comparing T-DXd with ado-Trastuzumab emtansine, where it yielded a median PFS of 28.8 months.

However, while efficacy is unquestionable, questions remain around treatment sequencing, duration, and long-term quality of life:

  • Could T-DXd be reserved for second-line therapy in select patients with less aggressive disease?
  • Might a strategy of T-DXd + P induction followed by de-escalation to maintenance Trastuzumab/Pertuzumab reduce toxicity?
  • Can biomarker-driven personalization, refine who should receive first-line T-DXd?

The researchers of this study emphasized that these results represent a paradigm shift in first-line treatment of advanced HER2-positive breast cancer.

Conclusion
DESTINY-Breast09 demonstrates that T-DXd + Pertuzumab significantly improves PFS compared to THP, with durable responses and manageable toxicity. The findings suggest a potential new first-line standard for HER2-positive metastatic breast cancer. While overall survival and long-term safety data are still maturing, the study sets a new benchmark in the frontline treatment landscape and invites critical dialogue on optimizing sequencing, duration, and patient-centered outcomes.

Trastuzumab Deruxtecan plus Pertuzumab for HER2-Positive Metastatic Breast Cancer. Tolaney SM, Jiang Z, Zhang Q, et al. for the DESTINY-Breast09 Trial Investigators. N Engl J Med. DOI: 10.1056/NEJMoa2508668

Routine Preoperative Breast MRI for Early-Stage Cancers May Not Be Beneficial: Outcome Data from Alliance A011104

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SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. It is estimated that in the US, approximately 321,910 new cases of female breast cancer will be diagnosed in 2026, and about 42,140 women will die of the disease, largely due to metastatic recurrence.

The Evolving Role of Breast MRI in Clinical Practice

Breast Magnetic Resonance Imaging (MRI) has become an important adjunct to mammography and ultrasound across a range of clinical scenarios. Its high sensitivity makes it particularly valuable in complex cases where conventional imaging may be limited, such as dense breast tissue or multifocal disease. As utilization has expanded, a critical question has emerged: does the additional disease detected by breast MRI translate into improved oncologic outcomes?

Established Clinical Indications for Breast MRI

Breast MRI is most clearly supported in selected high-risk and diagnostic settings, where its superior sensitivity can meaningfully inform care.

High-Risk Screening
MRI is recommended for patients with a substantially elevated lifetime risk of breast cancer, including those with:

  • Pathogenic BRCA1/2 variants or first-degree relatives of known carriers
  • Hereditary cancer syndromes such as Li-Fraumeni or Cowden syndrome
  • Prior therapeutic chest irradiation between ages 10 and 30
  • A calculated lifetime breast cancer risk of ≥20–25% using validated risk models

Evaluation of Known Breast Cancer (Staging and Extent)
In patients with newly diagnosed breast cancer, MRI may help define disease burden when conventional imaging is insufficient:

  • Detection of multifocal or multicentric disease, including contralateral breast involvement
  • Improved visualization in dense breast tissue
  • Enhanced detection of invasive lobular carcinoma, which can be underestimated on mammography
  • Identification of occult primary tumors in patients presenting with axillary adenopathy
  • Assessment of posterior lesions and potential chest wall involvement

Diagnostic Evaluation of Symptoms or Indeterminate Findings
MRI is also used selectively to clarify challenging diagnostic scenarios, including:

  • Pathologic nipple discharge or suspected Paget disease
  • Indeterminate mammographic or ultrasound findings that cannot be confidently biopsied
  • Evaluation of breast implant integrity
  • Unexplained new nipple inversion

Treatment Monitoring and Post-Treatment Assessment
In the therapeutic setting, breast MRI may assist with:

  • Monitoring response to neoadjuvant chemotherapy
  • Evaluating residual disease after breast-conserving surgery
  • Distinguishing post-treatment changes from locoregional recurrence

While these indications are well accepted, the impact of breast MRI on long-term outcomes in newly diagnosed breast cancer has remained uncertain.

Does Preoperative Breast MRI Improve Outcomes? Insights from Alliance A011104

Trial Rationale and Design

Despite widespread adoption of preoperative breast MRI for local staging and surgical planning, robust evidence demonstrating improved oncologic outcomes has been limited. The Alliance A011104 phase III trial was designed to directly address whether identifying mammographically occult disease with MRI, and modifying surgery accordingly, reduces local-regional recurrence.

This randomized study enrolled 319 patients with newly diagnosed clinical Stage I–II breast cancer who were eligible for breast-conserving surgery and had biologically aggressive disease, including Triple-Negative breast cancer or Hormone Receptor-negative/HER2-positive tumors. Patients with germline BRCA mutations, bilateral disease, or prior breast cancer were excluded. Participants were randomly assigned to undergo preoperative breast MRI within 30 days of diagnostic mammography or to proceed without MRI.

Patient Characteristics and Treatment

The median age at enrollment was approximately 59 years, with most patients presenting with small, node-negative tumors. Systemic therapy was commonly employed, with 85% of patients receiving chemotherapy and a subset treated in the neoadjuvant setting. Importantly, presurgical ultrasound, while not mandated, was widely utilized across institutions, reflecting contemporary practice.

Key Findings: No Improvement in Local-Regional Control

With a median follow-up exceeding five years, the trial demonstrated no significant difference in local-regional outcomes between the MRI and no-MRI arms.

  • Rates of breast-conserving surgery were high and comparable between groups
  • The majority of patients underwent sentinel lymph node biopsy alone
  • Pathologic Complete Response rates among patients receiving neoadjuvant chemotherapy did not differ significantly between arms
  • Adjuvant radiation use was similar in both groups

Among patients evaluable for the Primary endpoint, 5-year local-regional control exceeded 90% in both arms, with no statistically meaningful difference observed. Distant Recurrence-Free Survival and Overall Survival were also excellent and equivalent regardless of MRI use.

Exploratory subgroup analyses failed to identify any patient population that derived a local control benefit from preoperative MRI.

Interpreting the Results: Why Was No Benefit Observed?

Several explanations may account for the lack of observed advantage with preoperative breast MRI. First, contemporary multimodality therapy, including effective systemic treatment and radiation, may adequately control small foci of disease detected only by MRI, reducing the necessity for surgical excision. Second, advances in mammographic technology and the routine incorporation of ultrasound may have narrowed the incremental value of MRI for local staging compared with earlier eras.

Ongoing analyses from the trial are exploring whether MRI influences other surgical outcomes, such as margin status and reoperation rates.

Clinical Implications and Take-Home Message

In patients with early-stage Triple-Negative or HER2-positive breast cancer treated with modern multimodality therapy, local-regional recurrence rates are low. Results from Alliance A011104 indicate that routine use of preoperative breast MRI for local staging and surgical planning does not improve local-regional control in this setting.

These findings support a more selective, indication-driven approach to breast MRI, reserving its use for high-risk screening, specific diagnostic dilemmas, and carefully chosen staging scenarios, rather than routine deployment in all newly diagnosed patients.

As imaging technologies and systemic therapies continue to evolve, ongoing evaluation of how best to integrate advanced imaging into patient-centered, value-based care remains essential.

Effect of Preoperative Breast MRI Staging on Local Regional Recurrence (LRR) in Early Stage Breast cancer: Alliance A011104/ACRIN 6694. Bedrosian I, Ballman K, McCall LM, et al. Presented at the 2025 San Antonio Breast Cancer Symposium; December 9-12, 2025; San Antonio, TX. Abstract GS2-07.

Adjuvant Giredestrant Reduces Recurrence Risk in ER-Positive/HER2-Negative Early Breast Cancer: Results From the Phase III lidERA Trial

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SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. It is estimated that in the US, approximately 321,910 new cases of female breast cancer were diagnosed in 2026, and about 42,140 women will die of the disease, largely due to metastatic recurrence.

Background: Addressing Residual Risk in ER-Positive Early Breast Cancer

Estrogen Receptor-positive (ER-positive) breast cancer represents approximately 70% of all breast cancer diagnoses. Despite the widespread use of adjuvant endocrine therapy as standard of care for patients with ER-positive, HER2-negative early breast cancer, long-term outcomes remain suboptimal. Up to one-third of patients experience disease recurrence during or after completion of adjuvant endocrine treatment, underscoring a persistent unmet need for more effective and better-tolerated therapeutic options that can improve adherence and long-term disease control.

Giredestrant: A Next-Generation Oral SERD

Giredestrant is an investigational, oral, next-generation Selective Estrogen Receptor antagonist and Degrader (SERD). It is designed to completely block estrogen receptor signaling by preventing estrogen binding and inducing receptor degradation. Preclinical and early clinical studies have demonstrated that Giredestrant is more potent than earlier-generation SERDs and exhibits superior antiproliferative activity compared with Aromatase Inhibitors, including Anastrozole, in the neoadjuvant setting. These attributes provided the rationale for evaluating Giredestrant in the adjuvant treatment of ER-positive/HER2-negative early breast cancer.

The lidERA Trial: Study Design and Patient Population

The global, randomized, open-label Phase III lidERA BC trial (NCT04961996) evaluated the efficacy and safety of adjuvant Giredestrant compared with standard-of-care endocrine therapy in patients with medium or high-risk Stage I–III ER-positive, HER2-negative early breast cancer.

A total of 4,170 patients were randomized 1:1 to receive either Giredestrant 30 mg orally once daily or physician’s choice of standard endocrine monotherapy (Tamoxifen or an Aromatase Inhibitor). Premenopausal and perimenopausal women, as well as men, received concurrent LHRH agonist therapy. Treatment was administered for up to five years or until disease recurrence or unacceptable toxicity. At baseline, the median age was 54 years, with nearly 60% of patients postmenopausal. Disease stage distribution included 13% Stage I, 47% Stage II, and 40% Stage III disease. Median follow-up at the prespecified interim analysis was 32.3 months. The Primary endpoint was invasive Disease-Free Survival (iDFS), excluding second primary non–breast cancers. Key Secondary endpoints included Overall Survival (OS), iDFS including second primary malignancies, Distant Recurrence-Free Interval (DRFI), Disease-Free Survival, and Safety.

Efficacy Results: Clinically Meaningful Improvement in iDFS

At the prespecified interim analysis, adjuvant Giredestrant demonstrated a statistically significant and clinically meaningful improvement in invasive DFS compared with standard-of-care endocrine therapy. Treatment with Giredestrant reduced the risk of invasive disease recurrence or death by 30% (Hazard Ratio [HR] 0.70; 95% CI, 0.57–0.87; P=0.0014).

Three-year iDFS rates were 92.4% in the Giredestrant arm versus 89.6% in the standard endocrine therapy arm. Importantly, the iDFS benefit was consistent across all clinically relevant subgroups, including disease stage, menopausal status, geographic region, and prior chemotherapy exposure. Giredestrant also significantly improved Distant Recurrence-Free Interval, with a 31% reduction in the risk of distant relapse (HR=0.69; 95% CI, 0.54–0.89), reinforcing its potential to prevent metastatic progression.

Overall Survival data were immature at the time of analysis. However, a favorable trend was observed in the Giredestrant arm (HR 0.79), with continued follow-up planned for subsequent analyses.

Safety and Tolerability

Giredestrant was generally well tolerated, with a safety profile consistent with previously reported data. The most common adverse events included arthralgia, hot flushes, and headache, occurring at similar rates in both treatment arms. Grade 3–4 adverse events were infrequent and comparable between groups. Notably, treatment discontinuations due to adverse events were lower with Giredestrant than with standard endocrine therapy (5.3% vs 8.2%), suggesting favorable tolerability that may translate into improved long-term adherence in the adjuvant setting.

Clinical Implications

The lidERA trial represents the first Phase III study to demonstrate a significant benefit with an oral SERD in early breast cancer. By delivering superior invasive Disease-Free Survival, reducing distant recurrence risk, and maintaining a manageable safety profile, Giredestrant addresses key limitations of current adjuvant endocrine strategies.

Given the high prevalence of ER-positive breast cancer and the substantial proportion of patients who relapse despite standard therapy, these findings position Giredestrant as a compelling candidate for a new standard of care in appropriately selected patients with HR-positive/HER2-negative early breast cancer.

 Conclusion

Results from the Phase III lidERA trial establish adjuvant Giredestrant as a highly promising next-generation endocrine therapy for ER-positive, HER2-negative early breast cancer. The observed improvements in invasive Disease-Free Survival and distant Recurrence-Free Interval, combined with favorable tolerability and a trend toward improved Overall Survival, support Giredestrant’s potential to meaningfully improve long-term outcomes for a broad patient population.

Giredestrant vs standard-of-care endocrine therapy as adjuvant treatment for patients with estrogen receptor-positive, HER2-negative early breast cancer: Results from the global Phase III lidERA Breast Cancer trial. Bardia A, Schmid P, Martín M, et al. Presented at the 2025 San Antonio Breast Cancer Symposium (SABCS) (Abstract GS1-10)

INLURIYO® (Imlunestrant)

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The FDA on September 25, 2025, approved INLURIYO® , an estrogen receptor antagonist, for adults with estrogen receptor (ER)-positive, human epidermal growth factor 2 (HER2)-negative, estrogen receptor-1 (ESR1)-mutated advanced or metastatic breast cancer with disease progression following at least one line of endocrine therapy. INLURIYO® is a product of Eli Lilly and Company.

Neoadjuvant Niraparib Plus Dostarlimab in BRCA or PALB2-Mutated Triple Negative Breast Cancer: Phase II TBCRC 056 Results

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SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. It is estimated that in the US, approximately 316,950 new cases of female breast cancer were diagnosed in 2025, and about 42,170 women died of the disease, largely due to metastatic recurrence.

Rationale for a Chemotherapy-Free Neoadjuvant Strategy

Patients with germline BRCA1/2 or PALB2–mutated breast cancer represent a biologically distinct population with heightened sensitivity to PARP inhibition. Beyond synthetic lethality, accumulating preclinical evidence suggests that PARP inhibitors activate the cGAS/STING pathway, increasing intratumoral inflammation, recruiting CD8+ T cells, and potentially priming tumors for immune checkpoint blockade.

While prior studies have not demonstrated a clear benefit for combining PARP inhibitors with immunotherapy in the advanced TNBC (Triple-Negative Breast Cancer) setting, investigators hypothesized that the early-stage, neoadjuvant context, characterized by less immune exhaustion and lower tumor burden, might offer a more permissive environment for synergy.

Study Design and Patient Population

TBCRC 056 is a randomized, Phase II study evaluating the PARP inhibitor Niraparib (ZEJULA&reg;) in combination with the anti–PD-1 antibody Dostarlimab (JEMPERLI&reg;) as neoadjuvant therapy for patients with HER2-negative breast cancer harboring germline BRCA1/2 or PALB2 mutations. The trial includes cohorts for both triple-negative and Estrogen Receptor (ER) positive disease. The current analysis focuses on TNBC cohorts (Arms A and B). Participants with ER positive breast cancer will be placed directly into Arm C. There is no randomization for these participants.

Eligible patients were ≥18 years old with Stage I–III TNBC, primary tumors ≥1.0 cm, HER2-negative disease, and confirmed germline BRCA1/2 or PALB2 mutations. Patients were randomized to:

  • Arm A: Niraparib 200 mg orally once daily plus Dostarlimab 500 mg IV every 3 weeks for 18 weeks
  • Arm B: Niraparib monotherapy for 3 weeks followed by Niraparib plus Dostarlimab for 15 weeks

Tumor biopsies were obtained at baseline and week 3 to assess immune modulation. Surgery followed 18 weeks of therapy, with optional additional neoadjuvant treatment at investigator discretion if residual disease was detected.

RCB (Residual Cancer Burden in the breast tissue and axillary lymph nodes) Categories:

  • RCB 0:No invasive cancer cells found (pCR).
  • RCB I (Minimal):Very small amount of residual disease.
  • RCB II (Moderate):Moderate amount of residual disease.
  • RCB III (Extensive):Significant amount of residual disease.

Endpoints and Statistical Considerations

The Primary endpoints were:

  • Pathologic Complete Response (pCR; RCB-0) rate in Arms A and B combined
  • Change in stromal Tumor-Infiltrating Lymphocytes (sTILs) from baseline to week 3

The study was powered to detect a pCR rate of ≥50%, allowing rejection of a null hypothesis pCR rate <30%.

Baseline Characteristics

A total of 46 patients with TNBC were enrolled across Arms A and B. The median age was 39.3 years, reflecting the young demographic typical of germline BRCA-associated disease. Most patients were White (84.8%), with representation from Black, Asian, and Hispanic populations. Clinically, 37.0% had Stage I disease, 45.7% Stage II, and 17.4% Stage III. The majority had node-negative and high-grade (grade 3) tumors. BRCA1 mutations predominated (82.6%), with the remainder harboring BRCA2 mutations. No PALB2-mutated TNBC patients were enrolled in this cohort.

Efficacy Outcomes: pCR and Residual Disease

Neoadjuvant Niraparib plus Dostarlimab achieved a pCR rate of 50.0% (90% CI, 37.1%–62.9%) among evaluable patients, meeting and exceeding the study’s predefined efficacy threshold.

Notably:

  • pCR rates were identical in both treatment strategies, at 50% in Arm A (concurrent therapy) and Arm B (niraparib lead-in)
  • The combined RCB-0/I rate was 60.0%, suggesting meaningful tumor eradication or minimal residual disease in a majority of patients
  • Approximately 24% of patients crossed over to additional preoperative therapy, reflecting real-world decision-making when residual disease is identified

These findings support the robustness of the regimen regardless of initial PARP inhibitor lead-in.

Immune Modulation and Biomarker Insights

A key translational objective of TBCRC 056 was to characterize early immune changes within the tumor microenvironment.

Both treatment arms demonstrated statistically significant increases in sTILs from baseline to week 3:

  • Arm A: Mean sTILs increased from 16% to 27.4%
  • Arm B: Mean sTILs increased from 19.5% to 42.1%, suggesting a pronounced immune activation following PARP inhibitor exposure

Importantly, patients who achieved pCR had higher baseline sTIL levels than those who did not, underscoring the prognostic relevance of preexisting immune infiltration. Baseline sTILs were also associated with achieving RCB-0/I.

In contrast, baseline PD-L1 expression, estrogen receptor status (ER-0 vs ER-low), and short-term changes in sTILs were not independently associated with pCR, highlighting the complexity of immune–genomic interactions in BRCA-driven TNBC.

Safety and Tolerability

The safety profile of Niraparib plus Dostarlimab was consistent with known toxicities of PARP inhibition and immune checkpoint blockade.

  • Grade ≥2 treatment-related adverse events occurred in 82.6% of patients
  • Grade 3 events were reported in 26.1%, and grade 4 events were rare (2.2%)
  • The most common higher-grade toxicities included anemia, fatigue, hypertension, hypothyroidism, and neutropenia

Treatment discontinuation occurred in 13% of patients, with discontinuations split between Niraparib and Dostarlimab, suggesting manageable but clinically relevant toxicity in a neoadjuvant setting.

Key Takeaways for Oncology Practice

  • TBCRC 056 demonstrates that a chemotherapy-free neoadjuvant therapy with Niraparib combined with Dostarlimab achieved a 50% pathologic Complete Response (pCR) rate in patients with germline BRCA-mutated early-stage TNBC, exceeding the study’s predefined efficacy threshold.
  • pCR rates were identical whether Dostarlimab was administered concurrently with Niraparib or following a short PARP inhibitor lead-in, suggesting flexibility in treatment sequencing.
  • Treatment was associated with a significant increase in stromal Tumor-Infiltrating Lymphocytes (sTILs) within 3 weeks, supporting biologic synergy between PARP inhibition and PD-1 blockade in early-stage disease.
  • Higher baseline sTIL levels were associated with both pCR and minimal residual disease (RCB-0/I), whereas baseline PD-L1 expression and ER-low status were not predictive.
  • These findings support further investigation of biomarker-driven, non-chemotherapy neoadjuvant strategies in genetically defined TNBC populations.

TBCRC-056: A phase II study of neoadjuvant niraparib with dostarlimab for patients with BRCA- or PALB2-mutated breast cancer: results from the TNBC cohorts. Mayer EL, Graham N, Leon-Ferre RA, et al. Presented at: 2025 San Antonio Breast Cancer Symposium; December 9-12, 2025; San Antonio, TX. Abstract RF5-02.