Clinical pathologic features and differential diagnosis of 6 cases of anorectal malignant melanoma

Abstract

Objective To study the clinical and pathological characteristics and differential diagnosis and misdiagnosis reasons of primary anorectal malignant melanoma, so as to provide some references for the treatment and prognosis. Methods The clinical and pathological data of 6 patients with primary anorectal malignant melanoma treated at our hospital from January, 2005 to February, 2014 were retrospectively analyzed. And the patients were followed up. All the pathological specimens were immunohistochemically detected. Results 3 cases were misdiagnosed as hemorrhoids, 1 polyps, and 2 tumor. Microscope mainly showed solid flake or gland bubble structure and epithelioid or spindle shape tumor cells, leading to misdiagnosis for anorectal poorly differentiated adenocarcinoma in 4 cases and low differentiated squamous carcinoma in 1 case; the general pathological misdiagnosis rate was 83.3%. Tmmunohistochemical specific antibody S-100 of melanoma, Melan-A, and HMB-45 were all positive. All the 6 patients were followed up. Case 1 to 5 survived 30, 42, 26, 46, and 52 months, and case 6 refused chemotherapy after operation and survived 28 months. Conclusion Primary anorectal malignant melanoma is rare and its histomorphology varies, so it is easily be misdiagnosed as other malignant tumors. The follow-up found that the mass, infiltration depth, having lymph node metastasis, and not being treated with chemotherapy, and biological treatment can significantly shorten survival time. Surgery is the main treatment at present. Chemotherapy combined biological treatment for terminally ill patients can improve the patients’ prognosis but not very obviously. Key words: Anorectal malignant melanoma; Immunohistochemistry; Differential diagnosis; Prognosis