Harmonizing PD-L1 Testing in Metastatic Triple Negative Breast Cancer

How do you identify metastatic triple negative breast cancer patients who might benefit the most from immunotherapy (IO)? It is worth noting that discordance pervades the selection of patients for IO across various tumor histologies. Indeed, there are four anti-PD-L1 agents approved for PD-L1-restricted indications, together with four distinct companion diagnostic tests to assess the expression of PD-L1: nivolumab (28–8, Dako), pembrolizumab (22C3, Dako), atezolizumab (SP142, Ventana), and durvalumab (SP263, Ventana). Moreover, the complexity of PD-L1 assessment itself presents many key sources of variability. There is an urgent need to harmonize PD-L1 evaluation, maximizing cost effectiveness without losing accuracy.