Everolimus in Advanced Breast Cancer: A Systematic Review and Meta-analysis

Background Everolimus plus exemestane is approved for the treatment of hormone receptor-positive metastatic breast cancer (MBC) after progression on nonsteroidal aromatase inhibitors. The role of everolimus is less well defined in other breast cancer phenotypes and in combination with other drugs. Objectives We conducted a systematic review and meta-analysis to assess the efficacy and safety of adding everolimus to standard of care (SoC) in MBC regardless of tumor phenotype and treatment type. Methods The electronic databases PubMed and EMBASE were searched for eligible randomized trials. Pooled hazard ratios (HRs) for progression-free survival (PFS) and overall survival (OS) and pooled risk ratios (RR) and odds ratios for objective response rates, disease control rate (DCR), and grade 3 or higher toxicity were meta-analyzed. Subgroup analyses compared survival outcomes by tumor phenotype. Results Data from 2826 patients from eight trials were analyzed. The addition of everolimus to SoC reduced the risk of disease progression by 29% (HR 0.71; 95% confidence interval [CI] 0.56-0.90). This did not translate into an OS benefit (HR 0.95; 95% CI 0.80-1.13). In addition, everolimus improved the DCR (RR 0.82; 95% CI 0.68-0.98), whereas it increased the risk of developing grade 3 or higher toxicity. The PFS benefit was more prominent for patients with hormone receptor-positive (+)/human epidermal growth factor receptor 2 (HER2)-negative (-) disease. For the HER2 (+) subgroup, the PFS benefit was restricted to patients with hormone receptor (-) disease. Conclusions Everolimus reduces the risk of disease progression in hormone receptor (+) MBC. In patients with HER2 (+) disease, the benefit is limited for those with hormone receptor (-) disease. Given the approval and use of newer drugs in MBC, clinical trials and real-world data are needed to confirm the benefit of everolimus and define the best treatment sequence strategy to adopt in that setting.