Subcategorization of lung cancer based on tumor size and degree of visceral pleural invasion.

Background: Lung cancer staging system proposed in 2007 adopts detailed tumor size cut-off values. Alternatively, visceral pleural invasion is deemed an important prognosticator, but has not been easily incorporated into the staging system.
Methods: We studied 1,245 patients with resected nonsmall-cell lung cancer. Among patients with current pathologic stage IB (pT2N0M0) disease, those with worse prognosis were reclassified as stage IIA based on tumor size and degree of visceral pleural invasion defined by the Japan Lung Cancer Society: P0 = no pleural involvement beyond elastic layer; P1 = infiltration beyond elastic layer without exposure to pleural surface; and P2 = exposure to pleural surface.
Results: The current pT2 category was divided into five groups based on size (<or= 3, > 3 to <or= 5, and > 5 cm) and degree of visceral pleural invasion (P0-1 or P2). Five-year survival rates in patients with P0-1 tumors greater than 3 cm to 5 cm or less were significantly better (59.5%) than those with tumors greater than 5 cm or P2 tumors (37.5% to 47.3%; p = 0.0014); we defined these two groups as T2a and T2b, respectively, and classified T2aN0M0 as stage IB and T2bN0M0 as stage IIA together with the current T1N1M0. Five-year survival rates for the modified IB and IIA diseases were 70.6% and 60.4%, respectively (p = 0.0414).
Conclusions: Modified subcategorization of the pT2 category resulted in T2a (> 3 to <or= 5 cm and P0-1) and T2b (> 5 cm or P2). Detailed assessment of the degree of visceral pleural invasion could provide more information on tumor characteristics and complement the pathologic staging of lung cancer.