Fibrinolytic system in plasma and pleural fluid in malignant pleural mesothelioma.

The two major fibrinolytic activators, urokinase-type plasminogen activator (u-PA) and tissue-type plasminogen activator (t-PA) may play role in tumor spread and metastasis. Malign pleural mesothelioma (MPM) is a kind of tumor with predominantly local invasion and low incidence of distant metastasis. In this study, u-PA, t-PA and PA activator-1 (PAI-1) antigen and activity were measured in plasma and pleural fluid samples from patients with MPM, lung cancer and benign effusion. When compared to the control group, in MPM group, plasma u-PA and t-PA antigen levels were higher, but plasma u-PA and t-PA activity were comparable. PAI-1 antigen was also higher in MPM group. These findings were in contrast to the lung cancer group, in which both activity and immunologic measurement of u-PA and t-PA were higher, but PAI-1 antigen was similar as compared to the control group. It is concluded that excess t-PA and u-PA are balanced in complexes with PAI-1 in MPM, whereas the amount of PAI-1 in plasma is insufficient to overcome the elevated t-PA and u-PA, in lung cancer. Based on these findings, it may be suggested that the balanced fibrinolytic system is responsible for the low incidence of distant metastasis in MPM.