Oral malignant melanoma with colon metastasis mimicking melanosis coli: Case report

Abstract

Metastatic melanoma to the colon originating from oral mucosa, mimicking melanosis coli, is rare. This report describes, for the first time, such a presentation in a 54-year-old patient and highlights its most unusual histopathologic features. Clinical follow up with whole body PET CT using FDG revealed increased radiotracer uptake in the proximal descending colon. Subsequent colonoscopy identified multiple hyperpigmented lesions in the ascending and transverse colon suggestive of melanotic deposits. Biopsy of these lesions shows melanotic deposit in the lamina propria simulating melanosis coli, along with rare atypical cells infiltrating and wrapping around and the colonic crypts. Immunohistochemical staining for Melan-A and SOX10 was positive, confirming the diagnosis of metastatic malignant melanoma. This case underscores the importance of maintaining a high level of suspicion by the pathologist when interpreting colonic tissue samples in such clinical context, as histopathologic findings may be subtle and easily overlooked.