Giant melanotrichoblastoma

Trichoblastomas are benign skin tumors composed mostly of follicular germinative cells recapitulating the differentiation of hair follicles. Several variants of trichoblastomas have been reported, including pigmented trichoblastomas, melanotrichoblastomas, subcutaneous trichoblastomas, or giant trichoblastomas. We report a rare case of a pigmented trichoblastoma with abundant dendritic melanocytes. A 51-year-old Korean man had a round soft tissue mass on his back. The tumor was 6 cm in size and located in the subcutaneous fatty layer. On immunohistochemical stain for Melan A, numerous dendritic melanocytes were demonstrated in both pigmented and nonpigmented epithelial cell components. These cells were also positive for HMB45, and some of the dendritic melanocytes were positive for S-100 protein. With the aid of immunohistochemical staining, we diagnosed the tumor as a giant melanotrichoblastoma.