Immunotherapy trials using monoclonal antibodies 323/A3 and 17-1A that recognize Ep-CAM, including trials focused on cancer of the lung, currently are underway. Nevertheless, there have been few comprehensive evaluations of the expression of Ep-CAM in specific types of neoplastic processes, including cancer of the lung. The current study of 60 human subjects with squamous cell cancer (SCC) of the lung, selected at random, was undertaken (1) to examine the expression of Ep-CAM in SCC and associated uninvolved bronchial mucosa, bronchial epithelial hyperplasia, and dysplasia, and (2) to correlate the results with established prognostic indicators and survival of patients. In both the uninvolved bronchial mucosa and epithelial hyperplasia, the expression of Ep-CAM in luminal cells was significantly higher compared with its expression in the matched basal cells (P = .003, P < .0001, respectively). When Ep-CAM scores of basal and luminal cells present in uninvolved bronchial mucosa and epithelial hyperplasia were combined, we observed a statistically significant stepwise increase in Ep-CAM expression from uninvolved bronchial mucosa to epithelial hyperplasia to SCC, suggesting its involvement in malignant transformation of SCC. The expression of Ep-CAM was significantly higher in poorly to moderately differentiated SCC compared with well-differentiated SCC (P = .04). An increase in the expression of Ep-CAM with increasing size or local extent of the primary tumor approached statistical significance (P = .09). The expression of Ep-CAM increased significantly with increasing involvement of regional lymph nodes (P = .02). Similarly, the expression of Ep-CAM increased with the increasing TNM stages (P = .04). Kaplan-Meier Survival analysis using the same categorizations showed that increasing tumor size, nodal status, and stage were significantly associated with poor patient survival (P = .04, .01, .01, respectively). There was, however, no statistically significant association between patient survival and staining intensity of carcinomas for Ep-CAM. We conclude that expression of Ep-CAM increased during the progression of SCC of the lung and, therefore, may play a role in the carcinogenesis of this disease.