Complement Split Product C3D as a Tumor Marker

Abstract Circulating immune complexes (cIC) are found in patients with different types of cancer. These cIC may be biologically active and thus cause activation of complement. Therefore, we have tested if the level of complement split product C3d may be used as a tumor marker. We have quantitated C3d in EDTA - plasma by use of the so-called double decker rocket immunoelectrophoresis method (1). The C3d levels were analysed in 51 patients with breast cancer (samples taken before operation) and compared with the levels in age- and sex-matched healthy controls. Most of the patients had normal levels of C3d, but about 15 per cent had significantly elevated levels. Twenty-eight of the patients were followed after the operation, at regular intervals. The results of the C3d analyses were compared with the levels of cIC detected by a Clq - binding assay. Our results indicate that the C3d level is a poor tumor marker, but follow-up analyses of the C3d level might be useful in the assessment of the clinical status of individual patients.