The FDA recently approved pembrolizumab (Keytruda®, Merck & Co) with chemotherapy for patients with locally recurrent unresectable or metastatic triple-negative breast cancer (TNBC) for those whose tumors express PD-L1 (CPS ≥10) as determined by an FDA approved test. In addition, the FDA approved the companion diagnostic, PD-L1 IHC 22C3 pharmDx (Dako North America, Inc.), to select patients with TNBC for pembrolizumab. Efficacy was shown in KEYNOTE-355 (NCT02819518), a multicenter, double-bl...