[A Case of Prolonged Survival of a Patient with Gastric Cancer Despite the Development of Pembrolizumab-Induced Fulminant Type 1 Diabetes Mellitus].

The patient was a 70-year-old man who underwent distal gastrectomy for gastric carcinoma of the antrum. One year after surgery, the patient developed a recurrence in the cardia lymph nodes. Following chemotherapy, the patient underwent a total resection of the remnant stomach and recurrent lymph nodes 2 years and 10 months after the resection of the primary tumor. The patient was re-treated with chemotherapy following surgery; however, he relapsed again, and pembrolizumab was initiated. After the administration of the 10th round of chemotherapy, the patient suddenly developed thirst and polydipsia. Marked hyperglycemia(BS level, 900 mg/dL)and ketoacidosis were observed; therefore, the patient was diagnosed with fulminant type 1 diabetes mellitus. The patient's symptoms improved after insulin administration, and self-injection was initiated. The patient was treated with pembrolizumab for 2 years with no apparent recurrence. The incidence of type 1 diabetes mellitus as an irAE is approximately 0.5% in patients on pembrolizumab. Although this is a rare complication, early detection and therapeutic intervention are desirable, and attention in daily practice is necessary.