TIGIT and melanoma: Emerging studies have shown that cancer cells not only express inhibitory IC ligands but also inhibitory IC receptors including PD-1, TIGIT and TIM-3 in OAC [11], melanoma [22], pancreatic [15], gastric [18,20] cervical [23], lung [16,24], ovarian [25], endometrial [25] and colorectal cancer [26].