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)
