Visceral pleural invasion: pathologic criteria and use of elastic stains: proposal for the 7th edition of the TNM classification for lung cancer.

OBJECTIVE: To define the anatomic extent of visceral pleural invasion (VPI) and to assess whether elastic stains are useful to determine VPI in lung cancer. The elastic layer of the visceral pleura is not mentioned in the current International Union Against Cancer or American Joint Committee on Cancer staging documents.
METHODS: A Pub Med search (www.pubmed.gov) of the National Library of Medicine was made for all articles published between 1970 and 2007 in humans under the search terms lung cancer and pleural invasion. These were reviewed for data regarding the pathologic classification of extent of pleural invasion including the use of elastic stains in this assessment.
RESULTS: Six articles that addressed reported survival data using elastic stains to assess for VPI were reviewed. These articles defined P0 (T1) as lack of pleural invasion beyond the elastic layer, P1 (T2) as invasion beyond the elastic layer, P2 (T2) as invasion to the surface of the visceral pleura and P3 (T3) as invasion of the parietal pleura. In five studies, survival was shown to be significantly worse for VPI defined as P1 or P2 compared with P0.
CONCLUSIONS: Based on the currently available data, we propose that the next tumor, node, metastasis (TNM) revision by International Union Against Cancer and American Joint Committee on Cancer define VPI as invasion beyond the elastic layer (PL1) including invasion to the visceral pleural surface (PL2). The abbreviation PL for pleura is recommended rather than P to avoid confusion with the existing use of p (pathologic) TNM in distinction from c (clinical) TNM. We also recommend that elastic stains be used in cases when the distinction between PL0 and PL1 is not clear based on evaluation of hematoxylin and eosin sections.