[A CASE OF URACHAL CARCINOMA WITH HIGH FREQUENCY MICROSATELLITE INSTABILITY (MSI-HIGH) TREATED BY PEMBROLIZUMAB].

A 75-year-old woman was admitted to our hospital with suspected gastrointestinal perforation and underwent emergency surgery. Bladder perforation was revealed during the surgery, and she was referred to our department. We detected a tumor on the apex of the bladder and performed partial resection of the bladder. Based on histopathological examination, a diagnosis of urachal cancer was established. Gemcitabine and cisplatin (GC) therapy was administered as an adjuvant therapy because of the high risk of peritoneal dissemination. She had the purulent spondylitis and gluteus medius abscess at the first course of GC therapy. We stopped GC therapy within the first course due to the adverse events and decreased performance status. Computed tomography revealed tumor recurrence in the pelvis three months after discontinuation of GC therapy. As the companion diagnostics revealed MSI-High, we administrated pembrolizumab. She was taking prednisolone 5 mg for SLE, but stable disease was observed after 5 courses of pembrolizumab. However, pembrolizumab was discontinued for eight months due to the stent graft insertion for the common iliac artery aneurysm. She had progressive disease after eight months interval of treatment. We restarted pembrolizumab but she was hospitalized for tumor fever after a total of eight courses. The patient died a month later. This seems to be the first case wherein pembrolizumab was administered for urachal cancer with MSI-High.