PGP9.5: a marker for cellular neurothekeoma

Neurothekeomas are benign, predominantly cutaneous neoplasms that are divided histologically into myxoid, intermediate, and cellular types. Although it is generally agreed that the myxoid type of neurothekeoma has a neural origin, the lack of consistent immunoreactivity to neural markers and insufficient ultrastructural evidence of neural differentiation in cellular neurothekeoma have brought the origin of cellular neurothekeoma into question. In this report the authors show that immunoreactivity to protein gene product 9.5 (PGP9.5)--a broad neural marker--is positive in 100% of cases of cellular neurothekeoma using microwave antigen retrieval, as well as in all cases of myxoid and intermediate neurothekeoma. In contrast, immunoreactivity to S-100 protein is only positive in 3 of 12 cases of cellular neurothekeoma. These results show that PGP9.5 is a useful marker for identifying cellular neurothekeoma, as well as other types of neurothekeomas using the antigen retrieval method. The results are consistent with the notion that cellular neurothekeoma has a neural differentiation.