PD−L1 immunostaining: what pathologists need to know

BACKGROUND: Immune checkpoint proteins, especially PD-L1 and PD-1, play a crucial role in controlling the intensity and duration of the immune response, thus preventing the development of autoimmunity. These proteins play a vital role in enabling cancer cells to escape immunity, proliferate and progress. METHODS: This brief review highlights essential points related to testing for immune checkpoint therapy that histopathologists need to know. RESULTS: In recent years, several inhibitors of these proteins have been used to reactivate the immune system to fight cancer. Selection of patients for such therapy requires demonstration of PD-L1 activation on the tumor cells, best done by immunohistochemical staining of the tumor and immune cells using various antibodies with predetermined thresholds. CONCLUSIONS: Immune checkpoint therapy appears to be promising and is rapidly expanding to include a large variety of cancers.