Malignant Melanoma Metastatic to Gastrointestinal Tract: A Clinicopathologic Study

Malignant melanomas metastatic to the gastrointestinal (GI) tract show a wide range of histologic features, many of which can mimic primary GI malignancies. In this study, we evaluated the clinicopathologic features of 41 cases of malignant melanoma involving the GI tract. Thirty-two patients were men and nine were women; the average patient age was 51.7 years (range, 26-74 years). Twenty-eight patients had a history of malignant melanoma. Thirteen patients, however, did not have a prior history of malignant melanoma; on the basis of the clinical presentation and the behav ior of the GI lesions of these cases, they were presumed to be metastases from regressed or clinically undetected melanomas. The small intestine was the most common site. 12 patients had involvement of multiple GI sites. Clinical diagnoses at presentation included GI bleeding of unknown etiology, small bowel obstruction, rectal carcinoma, gastric ulcer, lymphoma, and cholelithiasis. The three major histologic patterns that mimicked primary GI neoplasms were carcinoma-like, carcinoid-like, and stromal sarcoma-like. The average survival times were 61.9 months after the diagnosis of primary melanoma and 14.4 months from the time of GI tract involvement. Site of malignant melanoma in the GI tract, histologic pattern, and history of a primary lesion outside GI tract did not show any prognostic significance. Although metastatic malig nant melanomas of the GI tract are rare, they should be considered in the differential diagnosis of primary GI tumors. Int J Surg Pathol 2(1):3-10, 1994