Expression of the epithelial L1 antigen as an immunohistochemical marker of squamous cell carcinoma of the lung.

The distribution of epithelial L1 antigen was evaluated in 139 bronchogenic carcinomas which had been classified by a panel of pathologists according to the WHO recommendation of 1981. L1 was not found in three large cell and 13 small cell carcinomas, but it was expressed by tumour cells in 67 of 69 squamous cell carcinomas (97%), in three of four adenosquamous carcinomas (75%), and in three of 49 adenocarcinomas (6%). The staining for L1 antigen was more diffusely distributed in the positive adenocarcinomas than in the squamous cell carcinomas. Its expression in squamous cell carcinomas was typically confined to relatively small tumour cell groups and never included a complete specimen. Semi-quantitative estimation of the immunostaining showed no clear relationship to the degree of differentiation and scores for proliferation, but L1 expression was negatively related to nuclear aberration (P less than 0.025) and malignancy scores (P less than 0.002). The good agreement between morphological classification and expression of L1 makes this a valuable marker in the diagnosis of lung carcinomas.