a The uncommon superficial spreading tumor of any size with its invasive component limited to the bronchial wall, which may extend proximally to the main bronchus, is also classified as T1a.

For the T2 category, visceral pleural invasion is defined as invasion to the surface of the visceral pleura or invasion beyond the elastic layer.  Based on a review of published literature, the IASLC Staging Committee recommends that elastic stains be used in cases where it is difficult to identify invasion of the elastic layer by hematoxylin and eosin (H&E) stains.  A tumor that falls short of completely traversing the elastic layer is defined as PL 0.  A tumor that extends through the elastic layer is defined as PL1 and one that extends to the surface of the visceral pleural as PL2.  Either PL1 or PL2 status allows classification of the primary tumor as T2.  Extension of the tumor to the parietal pleura is defined as PL3 and categorizes the primary tumor as T3. Direct tumor invasion into an adjacent ipsilateral lobe (i.e. invasion across a fissure) is classified as T2a.