PDCD1 and head and neck squamous cell carcinoma: Currently, phase I and phase II clinical trials using anti-TIGIT mAbs, alone or combined with anti-PD-1/PD-L1 mAbs, are ongoing to evaluate the safety and efficacy in patients with metastatic or locally advanced solid tumors, such as RCC, NSCLC, SCCHN, breast cancer, melanoma, and CRC (NCT02794571, NCT03119428, NCT03563716, NCT03628677, NCT04047862).