A case of marked rectal stenosis due to Douglas’ pouch metastasis of renal pelvic carcinoma successfully treated with salvage enfortumab vedotin: correlation between serum KL‐6 levels and tumor response

INTRODUCTION: We report a rare case of marked rectal stenosis due to Douglas' pouch metastasis of renal pelvic urothelial carcinoma successfully treated with enfortumab vedotin. CASE PRESENTATION: A 77‐year‐old female presented with difficulty in defecation and abdominal distension. She had received two courses of cisplatin plus gemcitabine followed by four courses of maintenance avelumab for postoperative lymph node metastasis of renal pelvic urothelial carcinoma. KL‐6 levels were elevated, and a computed tomography scan revealed an irregularly shaped large mass occupying Douglas' pouch, with marked rectal stenosis. Metastatic urothelial carcinoma was pathologically diagnosed, and enfortumab vedotin was initiated after colostomy. After 12 courses of enfortumab vedotin, metastatic lesions showed marked shrinkage and KL‐6 levels decreased. CONCLUSION: Enfortumab vedotin elicited a remarkable response in treating rectal stenosis due to metastasis of renal pelvic urothelial carcinoma in Douglas' pouch. Furthermore, serum KL‐6 levels were correlated with the severity of metastatic urothelial carcinoma.