Immune Checkpoint Inhibitors in Triple Negative Breast Cancer: The Search for the Optimal Biomarker

Phase III trials have investigated the utility of immunotherapy in previously untreated metastatic triple-negative breast cancer. Some studies showed no benefit while others demonstrated a clinically significant improvement in overall survival in the PD-L1 positive population. It is not yet clear which biomarkers are most useful, and assays for these biomarkers have not been standardized. Given the often serious and severe side effects of immunotherapy, it is important and necessary to identify predictive biomarkers of response and resistance in order to enhance patient selection. In this review, the authors discuss both the challenges of traditional biomarkers and the opportunities of emerging biomarkers for patient selection.