American Journal of Case Reports

Representative image of hematoxylin and eosin staining of the tumor (scanning microscopy). (A, B) Stromal infiltration of
polygonal tumor cells with pronounced cohesion, invading the colorectal mucosa.

Objective: Rare disease

Background: Gastrointestinal tract melanomas are usually of metastatic origin, with primary melanomas being relatively
rare. Controversy arises about the existence of primary melanoma in the gastrointestinal tract except in areas
where melanocytes exist. The appearance of primary colon melanoma is rare due to the embryological absence
of melanocytes in the large intestine, with some authors denying its existence at all.

Case Report: We present a clinical case of a female patient with a primary melanoma of the descending colon. The patient
came to the clinic with nausea without vomiting, abdominal swelling and pain, difficult and irregular defecation, and data on a tumor process of the left colon from the performed colonoscopy. Laparoscopic left hemicolectomy with lymphatic dissection was performed. The conclusion to be drawn from histological results was
that the malignancy is poorly-differentiated adenocarcinoma. However, the immunohistochemical examination
showed colon melanoma. Postoperative complete dermatological and ophthalmic examinations showed no evidence of a cutaneous or an ocular primary lesion, so we decided that this could be a primary colon melanoma.

Conclusions: Because of the colonoscopy we were able to make a detailed histological examination of the tumor, which allowed us to differentiate it from common colon adenocarcinomas. Surgical treatment is important in the removal of the primary tumor. The method of choice, with excellent postoperative results, is laparoscopic left
hemicolectomy with selective cut-off of the colic vessels at the site of separation and removal of the affected
segment together with the mesentery-bearing regional lymphatic basin.