Ann Thorac Surg 2004;77:1773
© 2004 The Society of Thoracic Surgeons
Invited commentary
Clifton F. Mountain, MD
Cardiothoracic Surgery University of California, San Diego 1150 Silverado St Suite 110 La Jolla, CA, USA 92037
e-mail: cmountain{at}ucsd.edu
Detailed studies of both the healthy and diseased pleura have been somewhat neglected. The pleura is an interesting and important set of membranes that actively transports both fluids and cells; and pleural involvement with lung cancer has a significant effect on prognosis. It has long been known that there are three histologically identifiable components that comprise the pleura: (1) a mesothelial membrane, lined by (2) an elastic membrane, and (3) underlying connective tissue. From the earliest publication (1974) of the TNM Lung Cancer Staging System, it was appreciated that any involvement with the visceral pleura was a significant adverse prognostic finding. This study provides objective evidence in support of that conclusion and, importantly, draws attention to the fact that the definition of "pleural invasion" was never provided in the staging rules. The authors demonstrate that malignant cells extending beyond the elastic layer (Hammar's p1) have an essentially equal impact on prognosis, whether or not they are on the mesothelial surface (p2). Accordingly, this study supports the current staging rules.
It should be noted that the International Staging System is derived from clinical observations alone, ie physical findings, biochemical tests, imaging studies, endoscopic findings, and biopsies. Therefore, it is doubtful that any accurate evaluation of the p1–p2 layers of involvement could be clinically made in most cases. Such evaluation, therefore, cannot be a part of clinical staging. Of interest also in this study is the additional data on the prognostic significance of other associated factors such as age, gender, histology, and tumor differentiation. I would encourage the authors to address the additional issue of interlobar pleural involvement.
