PDCD1 and head and neck squamous cell carcinoma: For instance, pembrolizumab, a PD-1 inhibitor, is approved by the FDA for treatment of metastatic melanoma,179 metastatic NSCLC,180 Hodgkin’s lymphoma,181 and metastatic head and neck squamous cell carcinomas.182 Although the proportion of patients who are eligible for the treatment is lower than that of imatinib-CML cases, this target-based approach provided a better treatment option compared to adjuvant chemotherapy.