The role of a new monoclonal antibody assay in the detection of recurrent breast cancer.

The immunoradiometric assay "CA 15-3", recently developed to measure a breast tumor-associated antigen, gave a mean serum value of 13.8 U/ml (S.D. 6.2) for this antigen in 156 non-cancer controls (36 biopsies for a benign breast lesion and 120 healthy controls). Setting a cut-off value of 30 U/ml (specificity 99.3%), only 3 out of 58 primary breast cancer cases were positive. In metastatic breast cancer, 11 out of 33 cases with limited recurrence (33.3%) and 36 out of 56 cases with extensive recurrence (64.3%) gave abnormal values in this assay, above the cut-off point, with an overall sensitivity of 52.8%; the difference between the sensitivity values in the two groups of recurrent cases was statistically significant (P less than 0.01). According to the findings of the present study, CA 15-3 has no role in the detection of primary breast cancer, but its usefulness in disease monitoring can be hypothesized, as circulating levels of the antigen seem to be dependent on the tumor mass.