The revised International System for Staging Lung Cancer is useful for classifying the anatomic extent of the disease in the major cell types of lung cancer: squamous cell carcinoma, adenocarcinoma (including bronchioalveolar carcinoma), large cell carcinoma and small cell carcinoma.

Implications of Biologic Factors
A pattern of heterogeneity is apparent in the biological behavior of lung tumors within groups of patients with similar anatomic staging and histologic classifications. Proceeding from basic research findings related to this observation, hundreds of protocols for investigating biologic prognostic factors have been developed. Studies of molecular genetic markers that could determine a different individual outcome within a similar stage of disease, of growth factors and receptors, and of pathologic factors, such as angiogenesis and cell proliferation, report good or bad outcomes according to the presence or absence of tumor and host factors^21-22. In order to apply these findings to the clinical setting, the results must be scientifically confirmed and reproducible²³. In the future new approaches to treatment that are effective across the spectrum of lung cancer may render the staging concept obsolete; however, at this time, anatomic staging continues to serve as the most valid indicator of prognosis, as a guide for treatment planning and a means for communicating the results of treatment for specific groups of patients.