Primary gallbladder melanoma in dysplastic nevus syndrome: report of case and literature review.

A case of gallbladder malignant melanoma in a 62-year-old woman is reported. The gallbladder, resected for tumor mass seen on ultrasound examination, revealed neoplastic epithelioid cells with dark granules in the cytoplasm. These cells with pigment were positive immunohistochemically for S-100, HMB45 and vimentin. The patient, affected by dysplastic nevus syndrome, had a history of a melanoma in situ in her left upper arm that was excised 11 years ago. This is only the second case reported to date of primary malignant melanoma in dysplastic nevus syndrome.