Background and design: Trichoepithelioma is a benign skin tumor with follicular differentiation, which sometimes is difficult to distinguish clinically and histologically from basal cell carcinoma. One of the most helpful differences is the histologic appearance of the stroma. CD34 is an antigen known to stain the spindle-shaped cells located around the middle portion of normal hair follicles. We have stained formalin-fixed, paraffin-embedded sections of 16 trichoepitheliomas and 19 basal cell carcinomas for CD34 (anti-HPCA-1, Becton Dickinson, San Jose, Calif) to detect differences in the staining pattern and to facilitate discrimination of these two types of tumors.
Results: The spindle-shaped cells surrounding the islands of trichoepithelioma cells were focally strongly positive for CD34. In all basal cell carcinomas, the spindle-shaped cells surrounding the nests of tumor cells were negative; in these areas only the blood vessels were positive with this antibody.
Conclusions: CD34 staining pattern differentiates between trichoepithelioma and basal cell carcinoma. CD34 stain may be helpful in distinguishing between these two tumors on small punch biopsies or in difficult diagnostic cases.