Mixed Neuroendocrine Carcinoma and Adenocarcinoma in a Patient With Ileal Pouch-Anal Anastomosis

ABSTRACT Neoplasia of the ileoanal pouch is uncommon, occurring in fewer than 1% of patients. Neuroendocrine carcinoma (NEC) is a rare neoplastic complication and can be difficult to diagnose due to symptoms overlapping with inflammatory pouch disorders. We describe a 36-year-old man with ileal pouch-anal anastomosis complicated by Crohn's-like disease of the pouch who underwent pouch excision for refractory disease. Histopathology revealed mixed poorly differentiated adenocarcinoma and NEC. Management may involve surgical resection for localized disease and systemic therapy for advanced stages. This case highlights the need to consider neoplastic processes, including NECs, in patients with persistent or atypical pouch symptoms.