Response to Neoadjuvant Chemoradiotherapy in a Patient with Mucinous Adenocarcinoma Arising from a Chronic Anorectal Fistula and Diagnosed by Transrectal Punch Biopsy: A Case Report

Mucinous adenocarcinoma arising from a chronic anorectal fistula is a rare condition. It is often confused with a hemorrhoid or perineal abscess, which consequently delays accurate diagnosis. Here, we report the case of a 58-year-old man with blood-tinged stool who reported a rectal mass, which was diagnosed as mucinous adenocarcinoma arising from an anal fistula. After initial computed tomography-guided needle aspiration biopsy had failed to provide an accurate diagnosis, transrectal punch biopsy was performed to obtained adequate tissue sample for confirmative histological diagnosis. The patient was successfully treated with neoadjuvant concurrent chemoradiotherapy followed by surgical intervention.