A 20-year-old patient diagnosed with a melanoma that was surgically removed was then treated with toripalimab. After three cycles, the patient developed an elevated blood glucose of 7.3 mmol/L (131.4 mg/dL) and weight loss; at the time they were treated with metformin and gliclazide. Two months later the patient presented with a fasting blood glucose of 20.7 mmol/L (372 mg/dL), Hb1Ac of 10.4%, positive for glycosuria, and no ketonuria. The patient was treated with IV insulin and discharged on subcutaneous injection of insulin aspart and insulin degludec. The gene discussed is INS; the disease is melanoma.