Rare Case of Large Bowel Obstruction due to Plasmacytoid Urothelial Carcinoma.

INTRODUCTION: The most common etiology of large bowel obstruction (LBO) is colorectal cancer. However, extrinsic compression may occur from cancer of other organs. Plasmacytoid urothelial carcinoma (PUC) is a rare subtype of urothelial carcinoma that can present aggressively as an intraperitoneal spread. This report describes a case of LBO caused by PUC, which initially presented a diagnostic challenge.

CASE PRESENTATION: A 68-year-old woman presented with hematochezia and abdominal pain. She had a history of recurrent bladder cancer, treated with chemotherapy and multiple transurethral resections of bladder tumor (TURBT). The third TURBT revealed invasive papillary urothelial carcinoma (UC; ≥pT2) with partial positivity suggestive of a plasmacytoid or lymphoma-like subtype, while the fourth showed noninvasive UC. CT revealed wall thickening and obstruction of the transverse colon near the hepatic flexure without enlargement of the lymph nodes. Colonoscopy showed luminal narrowing caused by edematous wall thickening, suggesting extrinsic compression. To establish a diagnosis, the patient underwent diagnostic laparoscopy, which revealed that the right side of the transverse colon and the greater omentum were firmly compressed together and immobile, with extensive peritoneal dissemination. An ileo-transverse colon bypass and excisional biopsy of the disseminated nodules were performed, leading to the diagnosis of PUC. Although the patient's postoperative course was initially satisfactory and oral intake was resumed, duodenal constriction caused by tumor invasion subsequently developed, necessitating the initiation of parenteral nutrition. After undergoing 2 courses of pembrolizumab, pulmonary edema with pneumonia occurred. Despite best supportive care, the patient died 69 days after the operation.

CONCLUSIONS: PUC is a rare and aggressive subtype of bladder cancer that frequently metastasizes, including to the peritoneum, which may lead to LBO. Although colorectal cancer is the most common cause of LBO, considering alternative differential diagnoses and planning appropriate subsequent management are essential in such cases.