Background: Mucinous adenocarcinoma arising from a chronic anorectal fistula is rare, with few reports in the literature. Such lesions can be misdiagnosed for the more common benign perianal abscess or fistula.
Methods: From our retrospective chart review, we identified three patients with chronic perianal fistula-in-ano who were subsequently found to have developed perianal mucinous adenocarcinoma on biopsy. We recorded the symptomatology, subsequent management and further follow-up of each patient.
Results: Two of three patients who received irradiation and chemotherapy were still alive during 28 and 24 months of follow-up, respectively without any evidence of distant metastasis. One patient with inguinal lymph node metastases died due to distant metastasis 6 months after diagnosis.
Conclusions: Fistula-associated perianal mucinous adenocarcinoma is an uncommon malignant transformation of chronic fistula-in-ano. MRI can provide important diagnostic information on patient with this suspicious inflammatory condition. Although radical resection of the tumour with abdominoperineal resection remains the surgical treatment of choice. Combined chemoradiotherapy may be appropriate for these patients with promising results.