[A collision cancer between urothelial carcinoma and malignant lymphoma of the urinary bladder: a case report].

A man in his 70's visited the Department of Internal Medicine due to lumbago that had first appeared two months previously. Abdominal computed tomography showed a low-density area in the liver and swelling of lymph nodes surrounding the abdominal aorta. Four months later, he was hospitalized on an emergency basis in a urology ward in order to control bladder tamponade. Cystoscopy revealed massive blood clots and a papillary tumor at the left wall of the urinary bladder. He underwent transurethral resection of a bladder tumor, and the pathological diagnosis was a collision tumor between urothelial carcinoma (G2, pTa) and malignant lymphoma (B cell type). He underwent a liver biopsy soon thereafter, and the pathological diagnosis was malignant lymphoma (as for the one found in the urinary bladder). Bladder tamponade was repeated, which was relieved after one course of chemotherapy for malignant lymphoma. He underwent six courses of chemotherapy (THP-CO), and he was well without recurrence of either malignant lymphoma or urothelial carcinoma with 3 years' follow-up. To our knowledge, this is the 14th reported case of a collision tumor in the urinary tract.