Metastatic Malignant Melanoma to the Descending and Sigmoid Colon, the Liver, and the Lung: Case Report and a Brief Review of the Literature

Metastatic melanoma to the gastrointestinal tract is frequently detected at autopsy but remains underdiagnosed during life because of nonspecific symptoms such as anemia, weight loss, and altered bowel habits. Colonic involvement is rarer than small-bowel disease and can cause occult bleeding or iron-deficiency anemia.

We report a man with a history of ulcerated T3N0M0 cutaneous melanoma resected four years earlier who presented with fatigue, 15-lb weight loss, intermittent melena, and iron-deficiency anemia (hemoglobin 8.2 g/dL). Colonoscopy revealed two ulcerated pigmented masses in the descending and sigmoid colon. PET-CT demonstrated FDG-avid colonic lesions with mesenteric and retroperitoneal lymphadenopathy, pulmonary nodules, and hepatic metastases; brain MRI was initially negative. Histopathology showed pleomorphic epithelioid cells containing melanin pigment with strong S100, SOX10, HMB-45, and Melan-A expression and negative cytokeratin and CDX2, confirming metastatic melanoma. Molecular analysis identified a BRAF V600E mutation.

Combination nivolumab and ipilimumab produced a transient partial response, but the disease progressed within five months, followed by failure of BRAF/MEK-targeted therapy. Surgical resection was not feasible due to disseminated disease. The patient died eight months after diagnosis.

This case underscores the aggressive course of colonic metastatic melanoma and highlights the importance of early recognition, molecular profiling, and multidisciplinary management.