Colonic Melanoma, Primary or Regressed Primary

Primary melanoma originating in the gastrointestinal tract is very rare and the majority of these tumors arise in the mucosa of the anus or rectum. A case of solitary colonic melanoma in a 79-year-old man is described with a review of pertinent literature. The surgically excised neoplasm was evaluated by routine histology and immunohistochemistry stains. Pathologic examination of the excised cecal mass revealed an 8 x 5-cm tan-pink mass with a central green-black necrotic area. Histologically, there were solid sheets of S100- and HMB-45-positive pigmented cells extending from the mucosal ulcerated surface through the bowel wall. The patient had no evidence of cutaneous or ocular primary melanoma. He remained free of recurrent disease 5 years after surgical resection of the colonic melanoma. The unique pathologic features and clinical outcome support the diagnosis of primary colonic melanoma in this patient.