PDCD1 and cancer: Another way of immune escape is the expression of immune checkpoint molecules by cancer cells such as PD-1, PD-L1, lymphocyte-activation gene 3 (LAG3), TIM3, T cell immunoreceptor with Ig and ITIM domains (TIGIT), V-domain Ig suppressor of T cell activation (VISTA) and human leukocyte antigen G (HLA-G) (Figure 1).