Value of CA 15:3 in the follow-up of breast cancer patients.

CA 15:3, a new tumour marker detectable by two monoclonal antibodies (115 D 8 and DF 3), was measured by an immunoradiometric technique on the ELSA solid phase. Sixteen percent of patients with localized breast cancer had CA 15:3 levels greater than 25 U ml-1, and levels increased with tumour size. CA 15:3 levels greater than 25 U ml-1 were found in 54% of patients with nodal involvement and in 91% of patients with metastatic breast disease. Measurement of CA 15:3 in 70 women with metastatic breast cancer and a normal CEA revealed positive CA 15:3 levels at diagnosis of the first metastasis in 66% of cases; 63% of these patients could be monitored with CA 15:3.