Serum CA 15-3 assay in the diagnosis and follow-up of breast cancer.

Serum CA 15-3 values were determined in 177 patients with primary breast cancer and in 41 with non-malignant breast disease. Increased preoperative serum CA 15-3 values (greater than 38 U ml-1) were observed in 7%, 17%, 64% and 67% of patients with stage I, II, III and IV disease, respectively and in none of the patients with benign breast disease. Patients with elevated serum CA 15-3 values had poor 3-year cumulative survival (27%). In the postoperative follow-up 9% of patients with no clinical evidence of disease, 33% with a single metastasis and 67% with two or more metastases had elevated values. Increasing or decreasing serum CA 15-3 values correlated with the clinical outcome in 26 out of 27 cases (96%), whereas serum values remaining in the reference range had no predictive value. At the time of recurrence elevated serum CA 15-3 values were also observed in patients with normal preoperative values. Increased serum CA 15-3 values preceded the clinical detection of tumour recurrence by up to 13 months. In conclusion, serum CA 15-3 levels had prognostic value in breast cancer, reflected the extent of clinically detectable disease and the presence of occult metastatic disease. Further research is warranted on the benefits of CA 15-3 assays in relation to adjuvant chemotherapy as well as the earlier detection and treatment of metastatic disease.