CA15-3 serum levels in breast cancer and other malignancies--correlation with clinical course.

Serum levels of the breast cancer-associated tumor marker CA15-3 were evaluated in three patient groups: breast, colorectal and ovarian cancer and in healthy subjects. Of 51 blood samples obtained from 31 patients with metastatic breast cancer (Stage IV disease), 98% had marker levels greater than 30 u/ml and 86% had levels greater than 50 u/ml. In contrast, of 49 samples from 42 patients with Stage I-II disease, 45% had levels greater than 30 u/ml but only 6% had levels greater than 50 u/ml (mean 29.5 +/- 18 u/ml). The mean level of the CA15-3 antigen in patients with Stage IV breast cancer and responding to therapy was 79.8 +/- 27 u/ml, while the mean level in patients not responding to therapy was 134 +/- 66 u/ml (P less than 0.02). The mean serial changes in CA15-3 levels for those responding to therapy was -28.4% while the mean change for those not responding to therapy was +44%. The mean marker level for 26 patients with colorectal carcinoma was 29.8 +/- 29 u/ml; 23% of these patients had levels greater than 30 u/ml and 7% had levels greater than 50 u/ml. No substantial difference was seen in those with active compared with nonactive colorectal carcinoma. The mean marker level for 14 patients with active ovarian carcinoma was 83 +/- 62 u/ml. Of these patients, 78% had CA15-3 levels greater than 30 u/ml and 50% had levels greater than 50 u/ml. All healthy subjects (n = 22) had marker levels less than 30 u/ml. We compared CA15-3 and CEA blood levels in the same patient population; 86% of patients with metastatic breast cancer (Stage IV disease) had CA15-3 levels greater than 50 u/ml while only 72% of these patients had CEA levels greater than 5 ng/ml. These findings suggest that the CA15-3 assay reflects the clinical course of patients with advanced breast cancer and may be superior to CEA as a monitor of therapeutic efficacy.