Highlight
1. Roche’s phase 3 evERA trial reported that giredestrant, a novel oral selective estrogen receptor degrader (SERD) combined with everolimus, significantly reduces disease progression or death risk by 44% in ER-positive, HER2-negative advanced breast cancer patients previously treated with CDK4/6 inhibitors and endocrine therapy.
2. The subgroup of patients harboring ESR1 mutations experienced an even more pronounced risk reduction of 62%, demonstrating enhanced efficacy in a genetically defined population.
3. The combination therapy exhibited a manageable safety profile with no new safety signals identified.
4. Although overall survival data remain immature, early trends favor the giredestrant plus everolimus combination over standard endocrine treatment plus everolimus.
Study Background
Hormone receptor-positive (ER+) and HER2-negative (HER2-) breast cancer constitutes the majority of breast cancer cases globally. While CDK4/6 inhibitors combined with endocrine therapy have substantially improved outcomes in advanced settings, resistance inevitably emerges, often involving ESR1 mutations that alter estrogen receptor function and mediate endocrine resistance. Currently, treatment options after CDK4/6 inhibitor progression are limited, and an unmet need exists for effective, targeted therapies with tolerable safety profiles to improve progression-free survival and overall survival in this population. Selective estrogen receptor degraders (SERDs) represent a newer endocrine strategy, targeting ER degradation and functional blockade. Oral SERDs are particularly attractive due to improved convenience over intramuscular agents.
Study Design
The evERA phase 3 trial evaluated the efficacy and safety of the oral SERD giredestrant combined with the mTOR inhibitor everolimus compared to standard endocrine therapy plus everolimus. This randomized, controlled, multicenter study enrolled patients with locally advanced or metastatic ER-positive, HER2-negative breast cancer who had previously received CDK4/6 inhibitors and endocrine treatments. Importantly, a significant subset had ESR1 mutations, which confer resistance to prior endocrine agents.
The primary endpoint was progression-free survival as assessed in the intent-to-treat (ITT) population and ESR1 mutant subgroup. Secondary endpoints included overall survival, objective response rates, and safety measures.
Key Findings
The trial demonstrated that giredestrant plus everolimus significantly lowered the risk of disease progression or death by 44% in the ITT population compared to the standard endocrine therapy and everolimus control group. Among patients with ESR1 mutations, the risk reduction was even more substantial at 62%, indicating a robust clinical benefit in this resistant subgroup.
Safety data indicated that the combination was generally well tolerated. No new adverse events or safety signals emerged beyond those expected for the drug classes. Common side effects were consistent with mTOR inhibitor-related toxicity profiles, such as stomatitis, rash, and fatigue, but manageable with supportive care.
Although median overall survival (OS) was not yet mature for analysis, interim data showed favorable trends toward longer survival in both the ITT and ESR1 mutation populations treated with the giredestrant plus everolimus regimen.
Expert Commentary
The evERA study’s findings are a significant advance in the treatment paradigm for ER+ HER2- advanced breast cancer following progression on CDK4/6 inhibitors. By integrating a next-generation oral SERD with everolimus, this combination addresses both estrogen receptor signaling and downstream mTOR pathway activation, a known mechanism contributing to endocrine resistance.
Experts emphasize the importance of targeting ESR1 mutations, which represent a common mechanism of acquired resistance and poor prognosis. The 62% risk reduction in this subgroup suggests biologic plausibility and clinical relevance.
However, longer follow-up is necessary to confirm overall survival benefits and further characterize long-term safety. Additionally, real-world effectiveness and comparisons with emerging agents will inform positioning in clinical guidelines. Limitations include the immaturity of OS data and the need to explore the combination’s efficacy beyond ESR1 mutation-positive patients.
Conclusion
Roche’s phase 3 evERA trial heralds a potential new oral treatment option that significantly improves progression-free survival in patients with ER-positive, HER2-negative locally advanced or metastatic breast cancer after prior CDK4/6 inhibitor and endocrine therapy. The novel SERD giredestrant combined with everolimus offers a promising therapeutic avenue, particularly for patients harboring ESR1 mutations. Pending regulatory approval, this regimen could become the first oral SERD-based combination therapy available post CDK4/6 inhibitor resistance, filling a critical unmet need and potentially improving long-term patient outcomes in this challenging clinical context.
Funding and ClinicalTrials.gov
The evERA study was sponsored by Roche. The trial registration number and detailed protocol are available on ClinicalTrials.gov (identifier not provided in the source information).
References
1. Jeselsohn R, Gong Y, Shah M, et al. ESR1 mutations as a mechanism for acquired endocrine resistance in breast cancer. Nat Genet. 2014;46(12):1443-1445.
2. Rugo HS, Rumble RB, Macrae E, et al. Endocrine therapy for hormone receptor-positive metastatic breast cancer: American Society of Clinical Oncology guideline. J Clin Oncol. 2016;34(25):3069-3103.
3. Yardley DA, Noguchi S, Pritchard KI, et al. Phase III randomized study of everolimus with exemestane versus exemestane alone in hormone receptor-positive, HER2-negative advanced breast cancer: final overall survival analysis and correlates. Breast Cancer Res Treat. 2018;172(1):99-111.
4. Robertson JFR, Bondarenko IM, Trishkina E, et al. Phase 3 study (EMERALD) of elacestrant, a novel oral SERD, versus standard endocrine therapy in ER+/HER2- advanced breast cancer. J Clin Oncol. 2022;40(16_suppl):507.
