Immune complexes in breast cancer patients as detected by C1q binding.

Levels of Clq binding activity have been measured in the sera of patients with benign and malignant breast disease. Cancer patients showed significantly higher binding activity than patients with gross fibrocystic disease. Clq binding levels were not related to levels of carcinoembryonic antigen, or rheumatoid factor. The Clq reactive material was identified as being precipitable with Protein A, and predominantly eluted in gel filtration fractions with a molecular weight of approximately 1 x 10(6). These studies indicate that Clq binding level may be of use in the differential diagnosis of benign and malignant breast disease.