Primary amelanotic melanoma of the rectum mimicking adenocarcinoma

摘要

Background: Malignant melanoma is usually readily diagnosed by the presence of melanin granules. Although amelanotic melanoma contains a few melanin granules, it is often difficult to differentiate from non-epithelial malignant tumors. Immunohistochemical staining may be needed to diagnose the condition.Case Report: This report describes a case of amelanotic melanoma of the rectum, which was originally suspected to be an adenocarcinoma, but was subsequently correctly diagnosed by immunohistochemical staining with HMB-45 antibody and by the presence of S-100 protein. A pinkish-red ulceroproliferative growth was located about 7 cm from the anal verge. The patient was treated by laparoscopic low anterior resection.Conclusions: Very few cases of amelanotic melanoma of rectum have been reported in the literature and there is only limited clinical experience with this disease. It appears to be a highly lethal tumor and may need much more aggressive treatment than that used for carcinoma of the rectum.