PDCD1 and head and neck squamous cell carcinoma: Tumors resistant to prior anti-PD-1/PD-L1 therapy, such as non-small-cell lung cancer (NSCLC), squamous cell head and neck carcinoma (SCCHN), RCC, and urothelial carcinoma (UC), and without available anti-PD-1/PD-L1 SoC therapy, such as ovarian cancer (OvCa) and microsatellite-stable CRC were included.