Endocrine therapy combined with a CDK4/6 inhibitor remains the established standard of care for patients with ER-positive, HER2-negative locally advanced or metastatic breast cancer. As resistance to endocrine therapy continues to challenge long-term disease control, next-generation estrogen receptor degraders are being developed to improve outcomes.

Giredestrant is an oral selective estrogen receptor antagonist and degrader designed to provide more complete ER pathway inhibition than conventional endocrine therapies. Previous studies demonstrated promising activity in both early-stage and post-CDK4/6 inhibitor settings, creating optimism for its use as a first-line treatment option. The Phase III persevERA BC trial compared giredestrant plus palbociclib with the current standard regimen of letrozole plus palbociclib in previously untreated ER-positive, HER2-negative locally advanced or metastatic breast cancer.

Safety Outcomes- The most common grade 3–4 adverse events (AEs) in the giredestrant arm were hematologic abnormalities associated with PALBO. Endocrine therapy discontinuations due to AEs were similar (6.5% with giredestrant vs. 5.5% with letrozole).

KOL Insights-

“The relatively small proportion of patients with non-visceral disease in persevERA BC may have limited the ability to fully capture the potential advantages of SERDs. A key hypothesis is that patients with non-visceral metastases could derive greater benefit from SERDs than from aromatase inhibitors, warranting further investigation.”– Expert Opinion

“While persevERA BC did not meet its primary endpoint, the ongoing Phase III pionERA BC trial is evaluating giredestrant in a higher-risk population of patients who relapse on adjuvant endocrine therapy or experience recurrence within 12 months of treatment completion. This setting may be more dependent on overcoming endocrine resistance, potentially allowing the unique mechanism of giredestrant to demonstrate greater clinical benefit. The results are expected to provide important insights into the optimal positioning of giredestrant in hormone receptor-positive metastatic breast cancer.”– Expert Opinion

Conclusion-

HR+/HER2− breast cancer is the most common breast cancer subtype, accounting for approximately 70% of all breast cancer cases in the United States. Despite significant advances in endocrine therapy and CDK4/6 inhibitors, disease progression and treatment resistance remain major challenges for patients with locally advanced or metastatic disease.

Endocrine therapy plus CDK4/6 inhibitor combinations remain the preferred first-line treatment approach for patients with ER-positive, HER2-negative advanced breast cancer, while ongoing studies continue to explore the role of next-generation estrogen receptor degraders in selected patient populations. Giredestrant plus palbociclib achieved a numerical improvement in progression-free survival and prolonged duration of response compared with letrozole plus palbociclib. However, the study did not meet its primary endpoint of statistically significant progression-free survival improvement. While the combination demonstrated a manageable safety profile and encouraging efficacy trends, the results were insufficient to establish superiority over the current standard-of-care regimen.