Staging and evaluating responses in malignant pleural mesothelioma

Abstract

Over the years a number of different staging systems for malignant pleural mesothelioma (MPM) has been suggested. It has not been easy to agree and to find a system which correlates with prognosis. As important for the prognosis as the stage is the sub-type of MPM: the epithelial sub-type has a much better survival than do the sarcomatous or mixed types, and patients with epitheloid tumors can occasionally survive many years, even decades, without any treatment at all. In this number of Lung Cancer, two articles illustrate the difficulties [1,2]. There are two main reasons for the difficulties: the anatomical setting and the peculiar way that MPM grows. The anatomy of the pleural space seems fairly straightforward, limited as it is by the rib cage, the diaphragm, and the mediastinal tissues. However, there are problems in deciding when MPM is limited to the pleural space and when it has actually spread beyond these limits. The largest problem is the costophrenic angle: it is the diaphragm which separates the sub-pleural connective tissue from the sub-peritoneal connective tissue, but the diaphragm actually has ‘‘holes’’ in its attachment to the chest wall where there is no anatomic boundary. Thus, whether staged by CT or any other imaging method or by surgery, there are large difficulties in deciding whether the tumor has actually spread and invaded the peritoneum, and one of the main reasons for recurrence after ‘‘radical’’ surgery is tumor tissue remaining in these locations.