Gastro-intestinal metastasis from Melanoma: Clinico-pathological clues

Metastasis from melanoma in the gastro-intestinal tract is a frequent event but, in the absence of an adequate clinical context and oncological anamnesis, it could be misdiagnosed by the pathologists. Moreover, amelanotic and/or poorly differentiated metastasis from melanoma in the gastro-intestinal tract can be easily underestimated.

We describe the histological features of gastro-intestinal metastasis from melanoma in a multi-centric cohort of 49 patients. In 24/49 patients, we were able to compare histological findings such as the growth pattern and the melanotic pigment also in the primary melanoma.

The epithelioid pattern is the most common growth pattern observed in gastro-intestinal metastasis (57 %), followed by the mixed pattern (41 %) and the spindled pattern (2 %). We documented a discordant growth pattern between metastasis and primary in 9/24 cases and the absence of melanotic pigment in 8/49 cases.

Our experience highlights that pathologists should take into account the possibility of gastro-intestinal metastasis from melanoma also in cases with spindled-cells/amelanotic lesions, without a previous anamnesis of melanoma asportation, and in cases of a discordant growth pattern with the primary. A correct clinical integration and an aware immunohistochemical approach are imperative to best manage the bioptic sample in order to investigate the biological profiling and therefore plan a personalizated therapy.