Understanding how clinical history and tumor genetics influence treatment outcomes is increasingly important in hormone receptor-positive (HR+)/HER2-negative metastatic breast cancer. ESR1 mutations are a recognized mechanism of resistance to endocrine therapy, creating challenges for treatment selection following disease progression. A large real-world study examined outcomes among patients receiving elacestrant, with particular attention to prior treatment exposure and genomic characteristics that may help inform individualized treatment decisions.
Researchers analyzed data from the GuardantINFORM clinical-genomic database, identifying 756 patients with ESR1-mutated metastatic breast cancer who received elacestrant between January 2023 and March 2024. Approximately 76% had previously received a CDK4/6 inhibitor, while 38% had been treated with chemotherapy. The analysis evaluated time to treatment discontinuation, time to next treatment, and clinical-genomic factors potentially associated with differences in outcomes. These measures provided insight into treatment patterns in routine clinical practice, outside the controlled environment of randomized clinical trials.
Across the study population, median time to next treatment was 6.4 months, while median time to treatment discontinuation was 4.6 months. Patients who had received one or fewer prior lines of metastatic therapy experienced a median time to next treatment of 8.8 months, compared with 6.0 months among patients receiving elacestrant in the third-line setting. These observations suggest that prior treatment history may be an important consideration when interpreting outcomes, although the observational design does not establish that earlier use directly improves treatment effectiveness.
Genomic characteristics were also associated with differences in treatment duration. Elacestrant outcomes were generally consistent across ESR1 mutation variants, including Y537S and D538G. However, patients with four or more concurrent ESR1 alterations had a shorter median time to next treatment of 5.2 months. Patients with co-occurring ESR1 and PI3K pathway alterations, including mutations involving PIK3CA, AKT1, or PTEN, also had a median time to next treatment of 5.2 months. These findings highlight the complexity of endocrine resistance and the potential value of evaluating multiple molecular characteristics when interpreting treatment outcomes.
Overall, the study provides additional real-world evidence supporting the clinical activity of elacestrant in appropriately selected patients with ESR1-mutated metastatic breast cancer. The findings also suggest that treatment history and genomic complexity may help explain differences in outcomes across patient populations. Because the analysis relied on retrospective sequencing and claims data, treatment-duration measures should not be interpreted as direct equivalents of progression-free survival. Further research may help clarify how these clinical and molecular factors can guide treatment sequencing and patient selection.
Source: Lloyd MR, et al. Clinical and Genomic Factors Associated with Elacestrant Outcomes in ESR1-Mutant Metastatic Breast Cancer. Clinical Cancer Research. PubMed | Full Text