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 will be diagnosed in 2025, and about 42,170 women will die of the disease, largely due to metastatic recurrence.
Background and Clinical Unmet Need
Approximately 70% of breast tumors express Estrogen Receptors and/or Progesterone Receptors. The most common subtype of metastatic breast cancer is Hormone Receptor-positive (HR-positive), HER2-negative breast cancer (65% of all metastatic breast tumors), and these patients are often treated with anti-estrogen therapy as first line treatment. However, resistance to hormonal therapy occurs in a majority of the patients, with a median Overall Survival (OS) of 36 months. With the development of Cyclin Dependent Kinases (CDK) 4/6 inhibitors, endocrine therapy plus a CDK4/6 inhibitor is the mainstay, for the management of ER+/HER2-negative metastatic breast cancer, as first line therapy. Even with this therapeutic combination, most patients will eventually experience disease progression, with up to 50% of patients acquiring ESR1 (Estrogen Receptor gene alpha) mutations after exposure to prior endocrine therapy in combination with CDK4/6 inhibitors. These mutations enable constitutive activation of the estrogen receptor, rendering tumors less responsive to traditional endocrine agents. Although Selective Estrogen Receptor Degraders (SERDs) such as Fulvestrant and Elacestrant are often used in this setting, their clinical activity is modest and limited by pharmacokinetic and mechanistic constraints, especially in heavily pretreated, endocrine-resistant disease.
A Novel Approach: Vepdegestrant and the PROTAC Platform
Vepdegestrant represents a first-in-class, oral PROteolysis TArgeting Chimera (PROTAC) designed to degrade the ER through direct engagement of the ubiquitin-proteasome system. Unlike traditional SERDs, which bind to and inactivate the ER before relying on indirect degradation pathways, Vepdegestrant forms a ternary complex between the ER and an E3 ubiquitin ligase. This results in efficient and targeted ubiquitination and subsequent degradation of the ER protein. Early-phase trials demonstrated that Vepdegestrant was well tolerated and exhibited promising antitumor activity in patients with heavily pretreated ER+/HER2-negative advanced breast cancer. This laid the foundation for VERITAC-2, the first Phase 3 study evaluating a PROTAC agent in oncology.
VERITAC-2: Study Design and Patient Population
Study Overview:
VERITAC-2 is a global, randomized Phase 3 trial comparing oral Vepdegestrant 200 mg once-daily continuously with Fulvestrant 500 mg intramuscularly days 1 and 15 of cycle 1 and day 1 of subsequent cycles, in postmenopausal women and men with ER+/HER2-negative advanced breast cancer, previously treated with a CDK4/6 inhibitor plus endocrine therapy. An additional line of endocrine therapy was permitted. However, patients previously exposed to SERDs or chemotherapy in the metastatic setting were excluded. A total of 624 patients (median age 60 years; 43% with ESR1mutation tumors) were randomized 1:1 to receive Vepdegestrant (N=313) or Fulvestrant (N=311). Approximately 80% were postmenopausal, and 20% had received two prior lines of therapy in the advanced setting. Patients were stratified by ESR1 mutation status and presence of visceral disease. The Primary endpoint was Progression-Free Survival (PFS) as assessed by Blinded Independent Central Review (BICR), first in the ESR1mutations subgroup and then in the overall population contingent on statistical assumptions. Secondary endpoints included Overall Survival (OS), Objective Response Rate (ORR), Clinical Benefit Rate (CBR), and Safety.
Key Efficacy Findings
In the ESR1-Mutant Population:
- Median PFS: 5.0 months with Vepdegestrant vs 2.1 months with Fulvestrant
- Hazard Ratio: 0.57 (95% CI, 0.42–0.77); P=0.0001
- 6-Month PFS Rate: 45.2% with Vepdegestrant vs 22.7% with Fulvestrant
- Objective Response Rate: 18.6% vs 4.0% (P=0.001)
- Clinical Benefit Rate: 42.1% vs 20.2% (P<0.001)
There was a 43% relative reduction in the risk of disease progression or death with Vepdegestrant compared with Fulvestrant. These results represent a statistically significant and clinically meaningful improvement in PFS and response outcomes among ESR1mutated patients, reinforcing the hypothesis that targeted ER degradation via PROTAC technology can overcome a key mechanism of endocrine resistance.
In the Overall Population:
- Median PFS: 3.7 months (Vepdegestrant) vs 3.6 months (Fulvestrant)
- HR: 0.83 (95% CI, 0.68–1.02); P=0.07
Although trends favored Vepdegestrant, the PFS difference in the unselected population did not reach statistical significance, underscoring the critical role of ESR1 mutation status as a biomarker of response to this agent.
Safety and Tolerability
Vepdegestrant was generally well tolerated, with most Adverse Events (AEs) being Grade 1 or 2. Grade 3 or more Treatment-Emergent AEs occurred in 23.4% receiving Vepdegestrant versus 17.6% with Fulvestrant. The most toxicities with Vepdegestrant were fatigue, elevated ALT/AST, nausea, vomiting and diarrhea. Discontinuation due to AEs occurred in only 2.9% of patients receiving Vepdegestrant. Importantly, gastrointestinal side effects, often limiting with oral SERDs, were infrequent and generally low-grade, reflecting the favorable tolerability of this novel agent.
Clinical Implications and Future Directions
The VERITAC-2 trial offers a landmark clinical validation for PROTACs in oncology. For patients with ER+/HER2-negative advanced breast cancer harboring ESR1 mutations, Vepdegestrant offers a statistically significant and clinically relevant advantage in Progression-Free Survival over Fulvestrant. The favorable safety profile, oral dosing convenience, and mechanistic novelty support its development as a next-generation standard of care in this biomarker-defined subgroup.
Although benefit was not observed in the all-comer population, the compelling results in ESR1mutated disease position Vepdegestrant as a precision endocrine therapy option that could reshape the treatment landscape. Ongoing investigations will clarify its role in earlier lines of therapy and in combination strategies, including with targeted or immunotherapeutic agents.
Conclusion
Vepdegestrant has emerged as a promising, targeted therapy for patients with ESR1-mutated ER+/HER2-negative advanced breast cancer who have progressed on prior CDK4/6 inhibitor plus endocrine therapy. As the first PROTAC to reach Phase 3, its success in VERITAC-2 signals the clinical viability of targeted protein degradation platforms in hormone receptor–driven malignancies.
Vepdegestrant, a PROTAC estrogen receptor (ER) degrader, vs fulvestrant in ER-positive/human epidermal growth factor receptor 2 (HER2)–negative advanced breast cancer: Results of the global, randomized, phase 3 VERITAC-2 study. Hamilton H, De Laurentiis M, Jhaveri K, et al. J Clin Oncol 43, 2025 (suppl 17; abstr LBA1000)
