[Gallbladder metastasis of melanoma: Immunohistochemical and molecular data of a case and review of the literature]

We report the case of a 57-year-old man, who is hospitalized for the surgery of a gallbladder mass associated by an increase in fluorodeoxyglucose-activity on positron emission tomography/computed tomography scan. This is an incidental finding occurring during monitoring of a skin melanoma. A cholecystectomy is performed. Microscopic examination identified an infiltration of the gallbladder wall by a proliferation of atypical pigmented spindled melanocytes with numerous mitoses. The immunohistochemical analysis confirmed the melanocytic nature of this proliferation with the staining of HMB-45, S100 protein and Melan-A. A complementary immunohistochemical (p16, desmin and BRAFV600E) and molecular (BRAF sequencing) study is performed. The results are consistent with the hypothesis of a gallbladder metastasis of a cutaneous melanoma is proposed. Gallbladder metastases of melanoma are exceptional. The aim of our work is to describe a new case with immunohistochemical and molecular characterization, to review the literature on this topic and to consider the main differential diagnosis (primary malignant melanoma of the gallbladder).