Rectal mucinous adenocarcinoma mimicking prostatic urothelial carcinoma: A diagnostic and therapeutic challenge

Rectal mucinous adenocarcinoma rarely invades the prostate and can mimic primary urothelial carcinoma, risking misclassification. A man in his late 60s presented with urosepsis, and transurethral resection of papillary prostatic fossa tissue was initially read as high-grade urothelial carcinoma with adenocarcinoma differentiation. Pelvic imaging showed a rectoprostatic mass, and multidisciplinary review of histology, immunohistochemistry, and molecular profiling confirmed colorectal origin. After total neoadjuvant therapy, the rectal primary achieved clinical complete response, but residual prostate-bed disease persisted along a fistulous tract, requiring close surveillance. This case highlights integrated diagnostic assessment and careful response evaluation.