Primary mucinous adenocarcinoma of the bladder in a conjoined twin with solitary kidney: A case report

Background: Primary mucinous adenocarcinoma of the bladder (PMAB) is a rare malignancy, constituting less than 2% of all bladder cancers. It can be confused with urachal adenocarcinomas due to the overlapping clinical and histopathological features. Patients often present with hematuria and irritative lower urinary tract symptoms, and diagnosis is often delayed. Case presentation: We report the case of a 26-year-old non-ambulatory male with a history of separation from a conjoined twin in 2004 with a solitary right kidney. He presented with hematuria and lower abdominal pain. Imaging revealed a dome-centered bladder mass. He underwent a biopsy, which showed under the microscope tumor cells composed of mucinous pools dissecting the muscle with floating mucin-lined glands and signet ring cells. Later, he underwent a radical cystectomy, which showed an intestinal-type lining with pools of extravasated mucin. Final immunohistochemistry showed CDX2, CK7, and CK20 positivity, with cytoplasmic β-catenin staining. These findings support the diagnosis of primary bladder mucinous adenocarcinoma. Conclusion: Although initial biopsy differential diagnosis favored a urachal-type adenocarcinoma, final cystectomy revealed extensive colonic-type metaplasia of the bladder and urethra, supporting a primary bladder origin linked to chronic irritation. This case highlights a rare presentation of PMAB in a patient with complex post-surgical anatomy due to separation from a conjoined twin.