Tumoral Melanosis of the Colon: A Rare Manifestation of Regressed Melanoma.

Tumoral melanosis (TM) is a rare manifestation of a benign, completely regressed malignant melanoma and mimics malignant melanoma. These lesions are often found in patients with a history of known or undiscovered metastatic melanoma at or around areas of prior malignancy, commonly on the skin. We describe a rare case of TM discovered in the colon on routine screening colonoscopy in a patient with a history of metastatic melanoma who was responding well to systemic immunotherapy. The pigmented lesion, although endoscopically malignant-appearing, was found on histopathology to be a benign accumulation of melanin-laden macrophages, consistent with TM.