Phase Ib clinical trials are underway investigating BAY2416964 and pembrolizumab in patients with advanced solid tumors [128], as well as IK-175 in combination with nivolumab in primary PD-1-inhibitor-resistant metastatic or locally incurable recurrent head and neck squamous cell carcinoma [129]. Here, PDCD1 is linked to head and neck squamous cell carcinoma.