2021 Volume 63 Issue 1 Pages 45-51
A 68-year-old man presented to our hospital with complaints of bleeding during defecation. Colonoscopy revealed a coarse nodular elevated lesion with white mucus on the rectum above the peritoneal reflection. The lesion was accompanied by dark brown pigmentation. A biopsy specimen of the lesion was obtained, and histopathological examination showed atypical round cells with melanin pigment that had proliferated to become a solid lesion. Immunohistochemical examination showed that the neoplasm was positive for S-100, HMB-45, and Melan A, which indicated that the lesion was a malignant melanoma. There was no pigmentation in the skin. Positron emission tomography showed abnormal uptake in the rectum and gallbladder. He underwent low anterior resection and cholecystectomy. He was diagnosed with primary rectal malignant melanoma with gallbladder metastasis.
