Complement C1-inactivator in the serum of patients with malignant disease.

Complement C1-inactivator (C1-IA) in serum was determined in 423 individuals. The normal range for the concentration of C1-IA in serum was calculated from values in 94 blood donors and the concentrations in the sera of 329 patients were determined in relation to this range. A significant correlation was found between widespread malignant neoplastic disease and increased quantity of C1-IA in serum. Determination of C1-IA may be used to evaluate the extent to which a malignant disease is disseminated.