PD-L1 testing based on the SP142 antibody in metastatic triple-negative breast cancer: summary of an expert round-table discussion

Triple-negative breast cancer (TNBC) is more aggressive than other breast cancer subtypes. TNBC is characterized by increased expression of Programmed Death-ligand 1 (PD-L1), a signal used by many tumors to escape the immune response. Expression of PD-L1 is a positive predictor of response to immunotherapy; therefore, it should be investigated in TNBC in order to select patients who may benefit from anti-PD-L1 therapies. While many PD-L1 assays are available, only the VENTANA platform with the anti-PD-L1 (SP142) antibody is licensed as a companion diagnostic device for selecting patients with metastatic/advanced TNBC who are candidates for treatment with atezolizumab. In this article, we provide a summary of an expert round-table discussion about PD-L1 testing, using the SP142 antibody in metastatic TNBC. Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype. Recent discoveries in TNBC have shown that the higher the expression of the surface molecule PD-L1 in the cancer cells, the better the response of patients to immunotherapy. While several tests or diagnostics assays for detecting PD-L1 exist, only the antibody anti-PD-L1 SP142 possesses proven diagnostic value for selecting metastatic TNBC patients eligible for atezolizumab immunotherapy. Throughout the present article, a group of experts discusses how to best carry out the assessment of PD-L1 status with this assay.