Trichoblastoma of the skin occurring in the breast. A case report.

BACKGROUND: Trichoblastoma is a rare benign skin appendage tumor constituted mostly of follicular germinative cells. It can arise on any part of the body except the palms, soles, nail units and mucosal membranes. No case of it in breast skin has been reported before. Furthermore, fine needle aspiration cytology findings on this lesion have not been described before. CASE: A 76-year-old female presented with a firm nodule in her left breast. The tumor was well demarcated, about 1.5 cm in diameter. Fine needle aspiration cytology revealed clusters composed of relatively uniform cells with a high nuclear/cytoplasmic ratio. In the midst of some clusters, the tumor cells had a more abundant cytoplasm. Fibrocellular interstitium or dense cyanophilic acellular material occasionally was attached to them. The tumor cells had oval or fusiform nuclei that had fine, evenly dispersed chromatin. To exclude a diagnosis of breast cancer, it is important to recognize that the clusters are composed of basaloid cells with focal squamous eddies and that there is at least focally peripheral palisading. The histopathologic diagnosis was trichoblastoma.