High-grade trichoblastic carcinoma arising in trichoblastoma: a rare adnexal neoplasm often showing metastatic spread.

It has been debated whether malignant transformation of trichoblastoma occurs. The concept was recently forwarded that basal cell carcinoma is as a malignant neoplasm of follicular germinative cells and should be named trichoblastic carcinoma to show its relationship to trichoblastoma. Almost all basal cell carcinomas are low-grade malignant neoplasms and develop metastases only very rarely, and if so, only after very long duration and untreated growth. Only rare basal cell carcinomas arise in trichoblastomas. Up to now there have only been two reports of high-grade trichoblastic carcinoma arising in trichoblastoma, showing systemic metastatic spread and death. We add two further cases of trichoblastic carcinoma with anaplastic nuclei, arising in trichoblastoma. One of the tumors arose in a small nodular trichoblastoma on the right forearm of an 84-year-old male patient. The other one was a trichoblastic carcinoma at the base of a trichoepithelioma on the right thigh of an 87-year-old woman with Brooke-Spiegler syndrome. Our cases emphasize that high-grade trichoblastic carcinoma develops via malignant transformation of trichoblastoma, and is very rare.