[PD-L1 : a natural immunosuppressor related to carcinogenesis. A pathologist's point of view].

The goal of this article is to emphasize the role of anatomopathology for the intratumoral detection of the immune checkpoint PD-L1. This molecule is one of the main targets in the anti-cancer immunotherapy. The binding of PD-L1 to its receptor PD-1 results in the inactivation of the cytotoxic T-cells, thus providing a mechanism of keeping immune reactions under control. This process can be circumvented by tumour cells to evade immune system. By blocking PD-1/PD-L1 binding, it is possible to reactivate T-cells targeting tumour neo-antigens. This article focuses on how PD-L1 works, on its implication in neoplastic processes, on the general principles of its therapeutic blockade, on the biomarkers underlying the treatment efficacy and on the practical implications of these biomarkers, especially in the anatomopathological practice.