Prognostic significance of circulating immune complexes in cancer patients

Circulating immune complexes (CIC) were estimated in 100 cancer patients and 25 healthy control volunteers by means of the polyethylene glycol (PEG) precipitation test and latex agglutination inhibition (LAI) test. Pathological levels of CIC were found in 47% of the patients by PEG precipitation test and in 59% of the patients by LAI test; both tests were positive in 33% of the patients. Consequently, the use of the two assays resulted in 73% seropositivity for CIC. The PEG precipitation test detects antigen-antibody complexes formed in the ratio of 2:1 (Ag2Ab), while the LAI test could detect immune complexes formed over an extended range of antigen-antibody ratio including complexes as small as 8S. CIC values were significantly higher by combined assays (P less than 0.001) as compared to individual assays (P less than 0.01) when compared with the control group. It was found that 75% of post-operative follow-up patients became seronegative for CIC in the combined assays, whereas the 25% of post-operative patients who remained seropositive for CIC showed recurrence within three months after surgery. Immune-complex deposition was demonstrated on malignant cells in vitro by direct immunofluorescence studies in 73.3% of patients, while 60% of patients revealed complement-fixing antigen-antibody complexes. It was found that 20% of patients showing positive immunofluorescence with anti-C3-antisera had decreased levels of CIC. Complement-mediated cytotoxic injury results in reduction of tumor cell mass and subsequent decrease in CIC. Necrotizing and leucocytoclastic vasculitis in the tumor mass was initiated by raised CIC levels in vivo in 71% of patients. Necrosis of malignant tumors was seen in 58% of patients, and hemorrhage in 36% of patients. These changes were considered to be an aftermath of immuno-complex vasculitis initiated by CIC.