Expression of p75 neurotrophin receptor in desmoplastic trichoepithelioma, infiltrative basal cell carcinoma, and microcystic adnexal carcinoma

The histological discrimination between desmoplastic trichoepithelioma, infiltrative basal cell carcinoma, and microcystic adnexal carcinoma encountered in small biopsies is challenging when only morphological criteria are applied. The objective of this study is to test the use of p75 neurotrophin receptor (p75NTR) as an adjunct aid in classification of these tumors. Immunohistochemistry for p75NTR antigen was performed on routinely processed biopsies of 37 desmoplastic trichoepitheliomas, 11 infiltrative basal cell carcinomas, and 9 microcystic adnexal carcinomas diagnosed by morphological criteria in conjunction with results of CK20 immunostains. Cases were analyzed for the extent and intensity of p75NTR expression. Diffuse immunoreactivity was defined as involving >90% of tumor cells. Of the 37 desmoplastic trichoepitheliomas, 35 (94%) displayed strong diffuse immunoreactivity of tumor cells, proving high sensitivity of the marker to detect this tumor. However, despite the fact that diffuse p75NTR expression reached statistical significance in differentiating desmoplastic trichoepithelioma from infiltrative basal cell carcinoma (Fisher exact test P < 0.0001) and microcystic adnexal carcinoma (P < 0.0016), specificity of the stain is unsatisfactory because strong diffuse expression of p75NTR by neoplastic cells was observed in 4 (36%) cases of infiltrative basal cell carcinomas and 4 (44%) cases of microcystic adnexal carcinoma. This study demonstrates a significant difference in p75NTR expression in selected sclerosing neoplasms of the skin. Nevertheless, the practical value of p75NTR as an adjunct marker in the differential diagnosis of these tumors seems to be limited because of significant overlap in amount of p75NTR immunoreactivity.