Late-Onset Metastatic Signet Ring Cell Adenocarcinoma Following Bladder Exstrophy Reconstruction: Diagnostic Discordance and Uncertain Primary Origin

Bladder exstrophy is an uncommon congenital anomaly associated with a heightened lifetime risk of malignancy, particularly following reconstructive procedures incorporating intestinal segments. We describe a 60-year-old man with a history of bladder exstrophy repair who presented with flank pain and microscopic haematuria. Initial imaging suggested a bladder lesion; however, histological examination revealed a villous adenoma without evidence of malignancy. Subsequent investigations identified extensive skeletal metastases. Biopsy of a bony lesion demonstrated metastatic adenocarcinoma with signet ring cell morphology. Immunohistochemical analysis showed positivity for CK20 and CDX2 and negativity for CK7, suggesting a gastrointestinal origin. Despite a comprehensive evaluation, no primary tumour was identified. Following a multidisciplinary team discussion, the patient was commenced on systemic chemotherapy and bone-targeted therapy for presumed colorectal carcinoma. This case highlights the diagnostic complexity associated with malignancy in reconstructed urinary tracts and emphasises the need for long-term surveillance in this patient population.