Involucrin expression in normal and neoplastic human skin: a marker for keratinocyte differentiation.

Involucrin is a recently recognized structural component of mature squamous epithelial cells. We examined involucrin expression using an immunoperoxidase technique in normal skin and in a variety of epidermal hyperplasias and neoplasms to determine whether distinctive staining patterns existed within these lesions. Four patterns of reactivity were observed: diffuse intracellular staining typical of keratinocytes of the upper third of normal epidermis and epidermal hyperplasias and benign neoplasms; staining at cell borders, seen principally in benign epidermal neoplasms; patchy staining characteristic of squamous cell carcinoma in situ; and absence of staining in benign and neoplastic basaloid epithelium. Invasive nests of squamous cell carcinomas were negative for involucrin reactivity, whereas pseudoinvasive tongues of epithelium at the bases of keratoacanthomas were focally positive. These results suggest that immunoperoxidase staining for involucrin may be useful in distinguishing certain benign from malignant epidermal neoplasms as well as in understanding the altered maturation and kinetics of proliferative processes afflicting keratinocytes.