Intestinal obstruction due to primary intestinal melanoma in a patient with a history of rectal cancer resectioning: A case report.

The vast majority of the cases of intestinal melanomas are metastatic lesions, originating from an occult primary cutaneous or ocular lesion, whereas primary small intestinal melanomas are extremely rare. This is a rare case of primary small intestinal malignant melanoma with intestinal obstruction in a patient with a prior history of rectal cancer resection. The patient was admitted for abdominal pain and obstipation. Following an overall inspection, the patient was subjected to surgical treatment and a small intestinal tumor was removed. The histopathological examination of the lesion revealed a diffuse neoplastic infiltration involving the entire thickness of the intestinal mucosa. The neoplastic cells exhibited marked atypia, pleomorphism and immunoreactivity to S-100, anti-melanoma antibody (HMB-45) and melanocyte/melanoma tumor antigen (Melan-A). The diagnosis of primary small intestinal melanoma was confirmed. The patient underwent an uneventful postoperative recovery and was administered adjuvant therapy. At the 3-month, 6-month and 1-year follow-up, the patient remained alive, with no signs of tumor metastasis and/or recurrence. In this case, the patient was repetitively assessed by abdominal computed tomography (CT) and plain film, confirming that the obstruction was caused by small intestinal melanoma. There was no association between the rectal cancer history and the melanoma. A definitive diagnosis requires detailed clinical, histopathological and immunohistochemical analyses.