The role of everolimus in metastatic breast cancer and possibilities of moving forward-a narrative review.

ABSTRACT

Background and Objective: In hormone-receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer endocrine-based therapies are preferred over chemotherapy. One of the treatment options is the combination of everolimus with exemestane or other endocrine drug in later lines mainly based on progression-free survival (PFS) results of the phase 3 BOLERO-2 trial. Altogether, clinical trials did not prove an overall survival (OS) benefit and considerable side effects hampered its application in the day-by-day practice. In recent years CDK4/6-inhibitors became a first-choice combination partner to the endocrine treatment, everolimus still has a place within the treatment armamentarium. Although everolimus is a targeted drug, there is no accepted predictive biomarker and further patient selection is not possible. However, several directions can be defined how to optimally use everolimus. For update information on everolimus treatment in breast cancer I have performed a literature search. Methods: I used the keywords "breast cancer" and "everolimus" and extended the search in PubMed from 01/01/2014 to 10/02/2023. I considered all phase 3 trials, the phase 1-2 trials with not repetitive information, studies with biomarker results and I also checked review articles to identify potential relevant other clinical trial reports. I also have made a search in clinicaltrials.gov for recently completed and ongoing trials. Key Content and Findings: I summarized the search results in this concise and brief report focusing on main trial results and ongoing research with everolimus. Conclusions: The most promising research directions seem to be further investigations for useable predictive biomarkers, for combinations with other targeted drugs (even in a triple combination) and for the feasibility of pharmacologically guided dosing method.