Involucrin in lung tumors. A specific marker for squamous differentiation.

Involucrin is a precursor of the cross-linked envelope protein or marginal band present in human stratum corneum. This study uses immunohistochemical techniques for localization of involucrin in histologic sections from 91 lung tumors in order to evaluate the usefulness of involucrin as a tumor marker in lung neoplasms. Although involucrin is absent from bronchial epithelium, it is expressed in cultured tracheal epithelial cell colonies and in bronchial mucosa with squamous metaplasia. Involucrin was present in all 25 cases of squamous and adenosquamous carcinoma. Staining was focal in 12 cases of squamous cell carcinoma and was most marked in the larger neoplastic cells in the center of squamous cell nests. Only two of 20 cases of adenocarcinoma revealed focal staining for involucrin, and these cases may represent adenosquamous variants. Six of 12 cases of large cell undifferentiated carcinoma stained for involucrin, indicating squamous differentiation, and seven cases of malignant mesothelioma were negative. Isolated involucrin-positive cells were present in two of 16 cases of small cell anaplastic carcinoma and one of 11 carcinoid tumors, identifying variants of neuroendocrine tumors with dual differentiation. Patterns of localization of involucrin in paraffin and frozen sections were compared with staining for cytokeratins in parallel sections. Immunohistochemical localization of involucrin comprises a specific marker for squamous differentiation in lung tumors.