Evaluation of a breast cyst fluid protein detectable in the plasma of breast carcinoma patients.

A radioimmunoassay has been developed for one of the major proteins isolated from human breast cyst fluid. Immunologically this protein is identical to a protein present in both human milk and saliva. Ninety-two normal women had plasma levels of this protein below 100 ng/ml (range 7-81 ng/ml; mean 31 ng/ml), and 85% had plasma levels below 50 ng/ml. More than one-half of the women with active gross cystic disease of the breast had plasma levels above 50 ng/ml. None of these women, however, had plasma levels above 150 ng/ml. A significant percentage of women with advanced breast carcinoma have been found to have plasma concentrations of this protein greater than 150 ng/ml.