To the Editor.—
The fibrous papule is a small sessile papule that commonly occurs in the central portion of the face. For a simple lesion, the fibrous papule has excited controversy regarding its histogenesis. Many have stated that the fibrous papule is related to nevus cell nevus.1-2 Others feel that this lesion is not related to nevus cell nevus, but represents a fibrohistiocytic lesion.3-4 We had the unusual opportunity to study a lesion from the nose, by immunohistochemical methods, that contained the histologic findings of both nevus cell nevus and fibrous papule (Fig 1).I used the avidin-biotin-peroxidase method and primary antibodies against factor XIIIa and S100 protein. Doublelabel methods were also used with antibody to factor XIIIa as the second antibody under study. Appropriate antibody controls were included in this assay. I found that nevus cells strongly expressed S100 protein, but did not contain factor XIIIa (Fig