PDCD1 and neoplasm: T cells express the immunological checkpoint protein PD-1, which interacts with its receptor on neoplastic and immune cells, PD-L1, leading to the inhibition of cytolytic antitumor responses, thereby promoting immunologic escape of tumor cells (Ferris, 2015; Gato-Cañas et al., 2017; Gong et al., 2018; Moskovitz and Ferris, 2018).