Malignant melanomas in the small intestine: a study of 103 patients

Malignant melanoma shows an unusual predilection to metastasize to the small intestine. A proportion of small bowel melanomas occur without history of an antecedent primary. We evaluated a group of patients with malignant melanoma in the small intestine to further our understanding of this disease.

We reviewed 103 cases of malignant melanoma in the small intestine (77 surgical resections and 26 autopsies) accessioned at the Armed Forces Institute of Pathology between 1945 and 1991 for demographic, chronological, and pathological features.

Mean age at time of primary was 45.6 yr for surgical and 34.1 yr for autopsy cases (p = 0.01). Mean age at time of small intestinal involvement was 52.2 yr for surgical and 42.7 yr for autopsies (p = 0.03). Primary lesions preceded intestinal disease by an average of 5.6 yr for surgical and 2.1 yr for autopsies. The age distribution of surgical patients with and without known primary melanomas at the time of small intestinal melanoma was not significantly different. The same was true for autopsy patients. Using regression analysis, the linear relationship of age at primary melanoma (AAP) on age at small intestinal melanoma (AASI) was given by AAP = 2.30 + 0.85 (AASI), and that of AASI on AAP was given by AASI = 3.94 + 1.02 (AAP) (r = 0.93 and p < 0.0001 for both regressions).

Our data and results support the concept that small bowel involvement by melanoma, even without a known primary, is most probably metastatic. The age at which an unknown primary occurred in cases of intestinal melanoma, or the age at which intestinal metastasis may appear in cases with known primary melanoma, can be estimated. There appear to be two subsets of primary melanoma: one that occurs among younger patients and is more aggressive with rapid metastasis and early death and one that occurs among older patients, is more indolent, and metastasizes less rapidly.