Long-Term Results with Everolimus in Advanced Hormone Receptor Positive Breast Cancer in a Multicenter National Real-World Observational Study

Simple Summary Everolimus is an oral drug used in patients with advanced hormone receptor positive, HER2 negative breast cancer. In this study based on a national French real-world cohort of more than 22,000 patients, we sought to evaluate the impact of everolimus on overall survival. Using statistical methods fit for real-world data, our findings suggest that the use of everolimus may favorably impact overall survival, and that it is very likely underused in this common clinical setting. Everolimus is the first oral targeted therapy widely used in advanced HR+/HER2- breast cancer. We sought to evaluate the impact of everolimus-based therapy on overall survival in the ESME-MBC database, a national metastatic breast cancer cohort that collects retrospective data using clinical trial-like methodology including quality assessments. We compared 1693 patients having received everolimus to 5928 patients not exposed to everolimus in the same period. Overall survival was evaluated according to treatment line, and a propensity score with the inverse probability of treatment weighting method was built to adjust for differences between groups. Crude and landmark overall survival analyses were all compatible with a benefit from everolimus-based therapy. Adjusted hazard ratios for overall survival were 0.34 (95% CI: 0.16-0.72, p = 0.0054), 0.34 (95% CI: 0.22-0.52, p < 0.0001), and 0.23 (95% CI: 0.14-0.36, p < 0.0001) for patients treated with everolimus in line 1, 2, and 3 and beyond, respectively. No clinically relevant benefit on progression-free survival was observed. Causes for everolimus discontinuation were progressive disease (56.2%), adverse events (27.7%), and other miscellaneous reasons. Despite the limitations inherent to such retrospective studies, these results suggest that adding everolimus-based therapy to the therapeutic sequences in patients with advanced HR+/HER2- breast cancer may favorably affect overall survival.