Behavior of antithrombin III, determined as protein concentration and biologic activity, in subjects with neoplastic disease.

Antithrombin III (AT III), the primary inhibitor of plasma protease coagulation proteins, was evaluated in groups of patients with different neoplastic disease. When compared with that of 25 health subjects, the mean value of AT III biologic activity was elevated in all groups, significantly in gastrointestinal (p less than 0.02) and lung (p less than 0.001) tumors, lymphoma (p less than 0.02) and in the group with various primary cancers (p less than 0.05). No difference was found between 46 patients tested under chemoradiotherapy and 216 patients who had not undergone therapy for at least 1 month. Four patients with clinical thrombosis had normal ATIII biologic activity. Of the 262 patients studied, 14 had low AT III biologic activity without clinical thrombosis and normal protein concentration. In 71 patients (27%) an excess of immunoassayable protein of 20% or more over biologic activity was found. Double immunoelectrophoresis performed in 5 of these showed for 3 patients an enlarged second are of precipitation. Moreover, no correlation was observed between the activity and protein AT III concentration (r = 0.05). The likelihood of the presence of circulating AT III-protease complexes is discussed.