[A Case of Bladder Plasmacytoma Diagnosed during Treatment of Multiple Myeloma].

A 78-year-old man was treated with Bortezomib, Lenalidomide, and Dexamethasone, for multiple myeloma. Two years after the start of treatment, the patient came to our department with a complaint of gross hematuria. Cystoscopy revealed a tumor on the left wall of the bladder. Urine cytology was negative. Magnetic resonance imaging (MRI) of the lower abdomen showed a slightly high signal on the T2-weighted image, indicating an intravesical mass lesion invading outside the bladder. Contrast-enhanced computed tomography (CT) also showed an intravesical mass and enlarged left external iliac lymph node swelling. Transurethral resection of bladder tumor was performed. The resection specimen showed tumor cells. The pathological examination revealed CD138 (+) and light-chain restriction. The patient was diagnosed with plasmacytoma. The patient was treated with radiation therapy for plasmacytoma of the bladder and surrounding lymph nodes, and then with daratumumab and dexamethasone for multiple myeloma for one year; however, the patient died because of worsening of multiple myeloma.