Secondary malignant melanoma of the gallbladder. A contribution to the differential diagnosis of pigmented lesions of the gallbladder

The history of gallbladder involvement by a malignant melanoma in a 65-year-old woman is reported. The gallbladder, clinically resected for cholecystitis, harboured a polypoid dark pigmented tumour. The tumour was identified as a malignant melanoma immunohistochemically by positive reactions for gp100 (HMB45), melan A, and MiTF. Clinically, the patient was treated for cutaneous malignant melanoma by local excision 10 years earlier. The literature of pigmented lesions of the gallbladder is reviewed. In conclusion, the most important differential diagnosis of pigmented lesions of the gallbladder is the secondary gallbladder melanoma.