Introduction
- Estrogen receptor-positive (ER+) breast cancer (BC) accounts for ~70-80% of all BC cases with many patients developing therapy resistance and metastatic disease.
- Capecitabine has long-remained a chemotherapy-backbone for hormone therapy-refractory metastatic BC (MBC) 1.
- However, response to capecitabine is highly heterogeneous with some patients achieving durable response and others showing eventual disease progression despite presenting with similar clinical disease 2,3.
- This variability highlights the lack of clinically-implementable predictive biomarkers for the efficacy of conventional chemotherapeutics, including capecitabine 4,5.
- Accurate and robust identification of patients who would derive the most therapeutic benefit from capecitabine while sparing the potential non-responders from unwarranted toxicity is crucial to improve patient outcome and quality of life.