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Primary amelanotic melanoma of the rectum mimicking adenocarcinoma

Manash Ranjan Sahoo, Manoj Srinivas Gowda, Raghavendra Mohan Kaladagi

(CUTTACK, India)

Am J Case Rep 2013; 14:280-283

DOI: 10.12659/AJCR.889089

Published: 2013-07-26

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.

Keywords: low anterior resection, Immunohistochemistry, Amelanotic melanoma