Experience with CA 15.3 as a tumor marker in breast cancer.

CA 15.3, a new tumor marker, is a glycoprotein antigen produced in greater amounts by breast tumor cells. It can be quantitatively detected, circulating in human serum or plasma, using an immunoradiometric assay with monoclonal antibodies. In order to evaluate the usefulness of the method and to determine the cut-off for metastatic disease, the CA 15.3 levels were determined in 78 patients (5 patients with breast fibroadenoma and 73 patients with breast cancer). The conclusions of the study are that the CA 15.3 is a useful parameter in the management of patients in different stages of the disease: levels above 36 U/ml are suggestive of metastasis, and above 86 U/ml are indicative of them. On the other hand, CA 15.3 does not seem to be helpful in the pre-operative differential diagnosis of breast lumps.