A case report of anal fistula-associated mucinous adenocarcinoma developing 3 years after treatment of perianal abscess

Abstract Background A long-standing (over 10 years) anal fistula is considered a fundamental cause of fistula-associated mucinous adenocarcinoma (FAMC). Perianal abscesses and anal fistulas are two sequential phases of the same anorectal infectious process. We experienced a case of FAMC which developed 3 years after the treatment of a perianal abscess. Case presentation A 68-year-old woman was admitted to our hospital because of progressive anal pain and a palpable tumor. She had a history of undergoing a drainage operation for a perianal abscess 3 years previously. A 15 × 15-mm tumor at the former drainage site was identified; transanal ultrasonography showed an intersphincteric fistula connecting to the tumor. A biopsy taken from the tumor demonstrated mucinous adenocarcinoma; the tumor was diagnosed as FAMC. Laparoscopic abdominoperineal resection was performed. Histopathology showed highly dysplastic cells lining the lumen of the anal fistula and poorly differentiated mucinous adenocarcinoma proliferating in the dermis and epidermis in the distal aspect of the fistula. Conclusions FAMC can develop within fewer than 3 years after the development of a perianal abscess and anal fistula.