The evolution and advances of biomarker use in clinical trials for breast cancer treatment-a narrative review

Cancer is characterized with enormous heterogeneity, including intertumoral heterogeneity and intratumor heterogeneity, which represents the main hurdle and challenges for therapy. The great success in the precision medicine and personalized treatment among all cancer types has been noted in breast cancer. Treatment for breast cancer has evolved in the past decades starting from CMF regimen (cyclophosphamide, methotrexate and fluorouracil) chemotherapy as the standard of care regardless of histological type in 1970s to the current stage of molecular subtype-based therapy which can also be known as biomarker-driven therapy. In response to this great shift of paradigm, clinical trials in breast cancer have evolved during the past several decades, while biomarkers are becoming prominently valuable in driving breast cancer research and drug development. By enabling early detection, identifying treatment responders and monitoring treatment response and therapeutic effects, biomarker-based clinical trial design will speed the development process and allow evaluation of multiple patient groups while biomarker-driven personalized treatment approaches will lead to better patient outcomes. This review provides an overview of the biomarker landscape in different molecular subtypes of breast cancer and the use of prognostic biomarkers in assisting in predicting therapeutic outcomes and monitoring recurrence in patients with breast cancer.