In cases where the diagnosis of ICI-DM is not immediately apparent, it can delay appropriate treatment and pose potential risks to the patient’s life.[4] This report describes a case in which the administration of a programmed cell death protein 1 (PD-1) inhibitor (Sintilimab) to a patient with squamous cell lung cancer triggered a flare-up of psoriasis vulgaris and the development of new-onset diabetes mellitus. The gene discussed is PDCD1; the disease is diabetes mellitus.