Abstract: Objective To investigate the clinical and pathological features of anorectal malignant melanoma(AMM). Methods The clinical pathological and follow-up data of 7 cases of anorectal malignant melanoma were collected. The clinical and histopathological features and immunophenotype was analyzed. Results Among the 7 cases, 5 cases were female, 2 cases were male, aged 50-68 years, the average was 61 years. The tumors located in the lower rectum in 1 cases, 2 cases of teeth near the line, 4 cases of anal anus. The structure and morphology of the cancer cells were diverse. The organizational structure were mainly diffuse, focal and acinar. The cellular morphology were mainly epithelioid, spindle and lymphocyte like. And the results of IHC showed the expression of the following three markers, vimentin, S-100 and HMB45, were strongly positive in cancer cells. However, the expression of CK, EMA and LCA were negative. And 2 cases of CEA expression were positive, LI Ki-67 was 20~50%. Conclusion Anorectal malignant melanoma is one kind of rare malignant tumor and its characteristic morphology, immunophenotype could be helpful for diagnosis and differential diagnosis.

Key words: Anorectal malignant melanoma, Clinicopathologic features , Immunohistochemistry, Differential diagnosis