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

needle aspiration biopsy is performed first and in case of failure, a diagnosis is made on the basis of surgical excision biopsy. Herein, we report a case of mucinous adenocarcinoma arising from chronic anal fistula that was successfully treated by neoadjuvant concurrent chemoradiotherapy followed by surgical management. In this case, a diagnosis was made on the basis of transrectal punch biopsy, and chemoradiotherapy was effective in reducing mass size and lymph node metastasis prior to surgical resection.