Malignant change in trichilemmal cysts: a study of cell proliferation and DNA content.

We have examined proliferative activity in a series of pilar and trichilemmal cysts using an antibody to proliferating cell nuclear antigen. In benign lesions proliferative activity was confined to the basal layers of the squamous epithelium. Lesions showing malignant change showed increased proliferative activity and were not confined to the basal layer. These findings were correlated with studies on DNA content using flow cytometry.