PD-L1 Combined Positive Score in Triple-Negative Breast Cancer

Kamel Abou Hussein, MD, explains why breast oncologists score programmed death-ligand 1 (PD-L1) using the combined positive score (CPS) rather than the tumor proportion score, since PD-L1 expression in breast cancer sits mainly in the immune microenvironment. Pembrolizumab remains the only approved immunotherapy in triple-negative breast cancer (TNBC), given first line with chemotherapy or antibody-drug conjugates for a CPS of 10 or higher, based on KEYNOTE-355. His center tests every new breast cancer for estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 status, then adds local 22C3 PD-L1 testing for metastatic TNBC, with results in 5 to 7 days. Dr. Abou Hussein treats the cutoff as strict and sometimes retests borderline results, given tumor heterogeneity. Adjuvant immunotherapy trials have been negative so far, with SWOG S1418 still pending, and he believes immunotherapy works best with chemotherapy while the tumor remains in place. Benjamin Levy, MD, compares this with borderline PD-L1 decisions in lung cancer.