Anti-PD-1 antibodies, including pembrolizumab, are reported to have not only general chemotherapy side effect, for example nausea, leukopenia, and more, but also characteristic autoimmune side effects like hypothyroidism, type 1 diabetes, hypopituitarism, colitis, and drug-induced pneumonitis due to excessive immune reaction [4, 5]. The gene discussed is PDCD1; the disease is type 1 diabetes mellitus.