Enhanced toxicity with CDK 4/6 inhibitors and palliative radiotherapy: Non-consecutive case series and review of the literature

Abstract

Current first-line systemic treatment in most patients with metastatic hormone receptor-positive, HER-2 negative breast cancer is an aromatase inhibitor in combination with a cyclin dependant kinase (CDK) 4/6 inhibitor. Frequently, these patients require palliative radiotherapy (RT) for symptomatic disease management. There is a paucity of data on the safety of combining a CDK 4/6 inhibitor with palliative RT, with conflicting case reports in the literature. We report on 5 cases at our institution where enhanced radiotherapy toxicity was observed when palliative doses of RT was delivered during or prior to treatment with a CDK 4/6 inhibitor. After review of pre-clinical and mechanistic data,..