Mucinous adenocarcinoma of perianal region: an uncommon disease treated with neo-adjuvant chemo-radiation.

Mucinous adenocarcinoma of the perianal region is an oncologic rarity posing a diagnostic and therapeutic dilemma for treating oncologists due to very few reported cases without definite therapeutic guidelines. It accounts for 2% to 3% of all gastrointestinal malignancies and are historically known to arise from chronic anal fistulas and ischiorectal or perianal abscesses. We hereby report a sporadic and interesting case of perianal mucinous adenocarcinoma in a 56-year-old male initially treated with alternative medicines and local surgery for recurrent fistula in ano of 2 years duration. He presented with complaints of discharging growth in perianal region, painful defecation associated with occasional blood mixed stools of 6 months duration. Incisional biopsy from the ulcer revealed mucinous adenocarcinoma. Contrast enhanced computed tomography (CT) scan and whole body positron emission tomography (PET) scan showed a localized perianal growth which was further confirmed with colonoscopy. With no pre-set treatment protocol for this rare entity, he was managed with neo-adjuvant concurrent chemo-radiation (CCRT) followed by abdominoperineal resection (APR) and adjuvant chemotherapy. Presently he is on 3 monthly follow-up since last 1 year post APR and adjuvant chemotherapy without any evidence of recurrence or distant metastasis. To the best of knowledge, our report may be one of the rarest cases of this disease entity where the duration of anal fistula was merely 2 years in contrast to the established criteria that the fistula precedes carcinoma by at least 10 years.