Mucinous adenocarcinomas of the buttock are rare and have an uncertain etiology and natural course. They are usually related to chronic anal fistulas, hidradenitis suppurativa, or Crohn's disease. Here, we report a case of mucinous adenocarcinoma associated with hidradenitis and contradictory immunochemistry results.

A 62-year-old man complained of recurrent abscesses of the buttock for 3 years. He had several scars and nodules in bilateral buttocks, with purulent discharge. The skin lesions did not appear to originate from the anus. The patient was diagnosed with recurrent abscesses due to hidradenitis suppurativa at the first visit. He showed purulent and subsequent mucin discharge in the first operation and was diagnosed with mucinous adenocarcinoma. Several examinations were performed to determine disease origin and staging. There were no significant findings or evidence of anal fistulas. Hence, he underwent wide local excision and V-Y advancement flap in the second operation. The final diagnosis was mucinous adenocarcinoma without any evidence of anal fistulas. Additional immunochemistry test results were negative for cytokeratin (CK) 7 and positive for CK20 and CDX2, with a colorectal origin. A pathologist suggested that the disease originated from a chronic anal fistula. The patient has remained free of recurrence for 24 mo.

Although the patient with mucinous adenocarcinoma showed an atypical course, immunochemistry helped detect the disease origin.

• Mucinous adenocarcinoma
• Anal fistula
• Hidradenitis suppurativa
• Wide excision
• Immunochemistry test
• Case report