Coagulation inhibitors in pulmonary cancer patients

Pulmonary cancer patients are known to have an elevated risk to suffer from thromboembolic complications. Because hereditary deficiencies of coagulation inhibitors antithrombin III, protein C and protein S are known to cause thromboembolic events it was the aim of our study to search for acquired alterations of these proteins in pulmonary cancer patients. We could demonstrate antithrombin III and protein C to be within the normal range in patients suffering from pulmonary carcinoma. In contrast, in patients suffering from metastatic pulmonary carcinoma bound protein S was increased, while free protein S was significantly reduced. In some patients the decrease of free protein S was comparable to the diminution observed in hereditary protein S deficient patients. A high positive correlation was observed between C4b-binding protein and bound protein S, indicating C4b-binding protein to be a regulatory protein for the shift from free and anticoagulatory active to bound and anticoagulatory inactive protein S. In conclusion, the decrease of free protein S is one source for thromboembolic complications in pulmonary cancer patients. For interpretation of altered free protein S levels it is useful to measure C4b-binding protein.