Mucinous adenocarcinoma, a type of adenocarcinoma, is common in anal fistulae. Adenocarcinoma is a malignant tumor of the glandular epithelium. Glandular epithelium belongs to epithelial tissues such as oral cavity, nasal cavity, digestive tract, respiratory tract, mesothelium on the surface of some organs, etc. The glandular cavity is dilated and contains a large amount of mucus, in which the cancer cells seem to float. Preferred sites are stomach and large intestine. Histopathological examination: More than 50% of mucinous adenocarcinomas contain extracellular mucus pools. Mucus can also be seen in the interstitial glands. Causes: Chronic inflammatory stimulation, tissue hyperplasia and fibrosis caused by recurrent fistulae are the main pathological basis of anal fistulae carcinogenesis, and failure to treat anal fistulae in a timely manner or irregular treatment leads to narrowing, distortion, poor drainage, pseudo-healing, coupled with repeated infections, scar tissue proliferation and poor local blood supply, resulting in a repeated infection with more The chronic purulent infection foci with more fibrous tissue proliferation provide favorable conditions for cancer. Under the long-term and repeated stimulation of inflammation, the glandular tissues of the infected fistula will be changed by chemotaxis, which will eventually lead to carcinoma. Drug stimulation: Long-term and extensive use of various topical drugs often stimulates the anus. Long-term chronic inflammatory stimulation stimulates abnormal tissue cell proliferation. Bacterial infection. Time to cancer of chronic anal fistula: many reported cases are more than 10 years old. One case was 10 years old (metastasis), one case was 4 years old, and one case was 2 years old. All of them had a long history of heavy alcohol consumption. This kind of malignant tumor evolved from chronic anal fistula is clinically different from the general anorectal cancer, there are usually no complaints of diarrhea or constipation in the early stage, and rectal irritation symptoms and blood in stool are also rare. The early manifestations are mostly concealed by the symptoms of perianal abscess or anal fistula, so its early diagnosis is difficult. The following features are often present: the symptoms of the original fistula are aggravated, the amount of fistula secretion increases, the pain is progressively increased, the nature of the fistula discharge changes, jelly-like or bloody fluid appears, sometimes mixed with necrotic tissue, and there is a special foul odor; a progressively enlarged mass appears at the site of the original fistula, and later it may rupture and fluid flows out. Some scholars believe that the lymphatic metastasis of anal fistula mainly spreads to the lower abdomen and inguinal lymph nodes, and the cancer grows slowly, so local excision is recommended. We believe that local excision should be cautiously performed, and extensive combined abdominal-perineal radical treatment is more appropriate, and inguinal lymph node dissection should be performed at the same time for those with metastasis. Therefore, clinicians should routinely perform histological examination for patients with chronic anal fistula and perianal abscess, especially for patients with long-term non-healing wounds and abnormal wound changes after anal fistula surgery, so as to achieve early diagnosis and early treatment.