Primary versus Metastatic Gastrointestinal Melanoma: A Rare Case and Review of Current Literature

Abstract

Gastrointestinal (GI) melanomas are a rare diagnostic entity. Although there have been cases of melanomas solely in the GI tract, many debate their true origin: the gut versus a distant, undetected primary lesion that regressed known as melanoma of unknown primary. We present a case that involved diagnosing a GI melanoma and then backtracking to find a possible primary source. We review the most recent literature regarding possible etiologies of primary GI melanomas and how to differentiate whether it has a primary, metastatic, or unknown origin.

Figure 1

Extended right hemicolectomy specimen containing a 5.6 cm exophytic, partially obstructing lesion (a). Histology of colon lesion showing sheets of medium- to large-sized tumor cells with irregular nuclear contours and vesicular nuclei, intermixed with numerous mitotic figures ((b), hematoxylin-eosin, 400x). Immunohistochemistry of colon lesion diffusely positive for melan-A (c). PET scan showing areas of metastatic disease (left renal mass, L1 vertebral body), but prominent intensity of the left inguinal region and left anterior thigh (d). Endoscopy showing one of many pigmented lesions throughout the stomach (e).