Immunostaining for CD34 to Determine Trichoepithelioma-Reply

Our thanks to Drs Bryant and Pennys for their interesting and helpful comments concerning our study of CD34 staining in basal cell carcinomas and trichoepitheliomas.1While we have not yet encountered a basal cell carcinoma with strong staining immediately adjacent to the epithelial neoplasm, we have seen an occasional trichoepithelioma with only focal positivity, subsequent to our initial report. In these cases, however, other areas were found that demonstrated the typical CD34 staining of trichoepitheliomas that we reported. The slight variability in staining pattern is not entirely surprising, as it is not reasonable to expect any diagnostic test to be 100% sensitive and 100% specific. We have not encountered the difficulty in the interpretation of CD34 staining cited by Bryant and Pennys. In fact, in the vast majority of our cases, the staining has been quite strong, with very little background staining of collagen. Based on our initial impressions