PDCD1 and cancer: Cancer cells often use immune checkpoint molecules, such as programmed cell death protein 1 (PD-1)/PD-L1 (CD274), lymphocyte activation gene 3 (LAG3, CD223), CTLA4, hepatitis A virus cellular receptor 2 (HAVCR2, TIM3), and T-cell immunoreceptor with Ig and ITIM domains (TIGIT), to suppress the immune system and continue their malignant growth [50,51].