been suggested that the incidence of anal cancer is 0.1%. From 1995 to 2010, Beijing Erlong Road Hospital treated a total of around 50,000 patients with anal stula. In 1995, 2008, 2009, and 2010, a total of four male patients with mucinous ade­nocarcinoma were found. Their ages ranged from 52 to 69, with an average age of 58.6. All of the four patients had chronic perianal stula with repeated rupture and no recovery and with pus and blood and mucus-like substance spillage. The medical history was 7–15 years, with an average of 10.2 years. Two to six anal stulas were performed before diagnosis. The common clinical features are long-term postoperative wound nonhealing, abnormal hyperplasia of granulation tissue, mucus-like secretion from the wound, and occasionally eczema-like changes in the skin around the wound. The nal diagnosis was conrmed after 4–5 biopsies, the pathologi­cal interval of biopsy was 2–4 months, and the nal pathological report was mucinous adenocar­cinoma. All the four patients were excluded from intestinal and extra-intestinal tumors by colonos­copy, chest radiograph, and abdominal ultra­sound before surgery. No tumor tissue was found in the anal stula during operation, and the pri­mary colorectal anal tumor could be excluded, meeting the diagnostic criteria for secondary can­cerization of anal stula.