[Colorectal melanoma: review of two distinct forms of presentation].

Malignant melanoma of the colon and rectum is an infrequent disease. Primary anorectal melanoma accounts for 0.1-4.6% of all malignant neoplasms of the anal canal. Melanoma metastatic to the colon is symptomatic only in 4.4% of patients with a primary melanoma at another site and most of these tumors are diagnosed postmortem. We report two cases of colorrectal malignant melanoma. The first case concerned a patient with rectal bleeding who was diagnosed with a rectal lesion compatible with melanoma. Abdominoperineal resection was performed due to positivity of the sentinel lymph node. We discuss the utility of sentinel lymph node detection in this kind of tumor. In the second case, we discovered a polyp compatible with metastatic melanoma in the transverse colon in a patient with a previous diagnosis of melanoma. In both surgical specimens, the diagnosis of melanoma was confirmed by positivity for protein S-100, Melan-A and HMB-45.