Visceral pleural invasion classification in non-small cell lung cancer: a proposal on the basis of outcome assessment

OBJECTIVE: The definition of visceral pleural invasion in lung cancer TNM classification of the International Union Against Cancer lacks detail. The purpose of this study was to evaluate the significance of the extent of pleural involvement as a prognostic factor and to propose a refined TNM classification on the basis of visceral pleural invasion. METHODS: We reviewed 1653 consecutive patients with T1, T2, and T3 surgically resected non-small cell lung cancer for their clinicopathologic characteristics and prognoses. Visceral pleural invasion was classified by using the Japan Lung Cancer Society criteria: p0, tumor with no pleural involvement beyond its elastic layer; p1, tumor extension beyond the elastic layer but no exposure on the pleural surface; and p2, tumor exposure on the pleural surface. RESULTS: The 5-year survivals for patients with p1 or p2 tumors of 3 cm or less were identical and significantly worse than those for patients with p0 tumors of the same size. Patients with p1 or p2 tumors of greater than 3 cm and patients with T3 cancers had essentially identical survivals. CONCLUSIONS: Visceral pleural invasion should be defined as tumor extension beyond the elastic layer of the visceral pleura, regardless of its exposure on the pleural surface. A tumor of 3 cm or less with visceral pleural invasion should remain classified as a T2 tumor, as presently occurs in the International Union Against Cancer staging system, and tumors of greater than 3 cm with visceral pleural invasion should be upgraded to T3 status in the International Union Against Cancer TNM classification.