Human lung cancer—a comparative study of the levels of circulating immune complexes in pulmonary blood draining the tumor area and peripheral venous blood

Our objective was to investigate whether low levels of circulating immune complexes (cICs) in peripheral venous blood of cancer patients could be due to removal of cIC released at the tumor site during passage to the peripheral veins. In 54 patients with primary lung cancer, we therefore compared the cIC levels as detected by 3 different assays in paired samples from the pulmonary vein draining the tumor area and from a peripheral vein. Only 6 of the 54 patients had significantly increased pulmonary vein cIC levels as compared to the corresponding peripheral vein levels. The peripheral vein levels of these 6 patients were all within the normal range, and in none of these patients was the difference between the 2 sites of analysis—although significant—of such a magnitude that the pulmonary vein cIC level appeared higher than the normal range, i.e., “positive” for cIC. Positive cIC levels were only found in 11% of lung cancer patients (irrespective of the site of measurement). Thus, our present data, together with our previous findings indicating no significant difference between peripheral venous blood cIC levels in cancer patients and normal controls, contradict the theory of tumor cells expressing new antigens resulting in the formation of tumor‐associated cICs.