Comparison of CA15-3 and carcinoembryonic antigen in monitoring the clinical course of patients with metastatic breast cancer.

Fifty-three women with metastatic breast cancer and serial plasma samples were selected to study the correlation between disease course and variations in circulating CA15-3 and carcinoembryonic antigen (CEA) levels. Forty-nine patients had their first sample drawn at the beginning of therapy, while four patients did not receive any treatment during the period of study. Clinical course was scored as progressive disease (PD), responsive disease (RD), and stable disease on the basis of radiological and physical evaluations. The percentage of variation in antigen level between the initial sample and samples drawn at the time of the clinical evaluation was correlated with clinical course. CA15-3 levels above 22.0 units/ml and CEA levels above 3.0 ng/ml were considered elevated values. Antigen levels that increased greater than or equal to 25% and decreased greater than or equal to 25% from the initial value were considered to correlate with PD and RD, respectively. Variations in antigen levels +/- 25% from the initial value were considered to correlate with stable disease. Significantly more patients had elevated circulating levels of CA15-3 than CEA (96.2 versus 69.8%; P less than 0.01) at some point in the course of disease. Overall, CA15-3 correlated with disease progression, regression, or stability in a higher number of patients than CEA (60.3 versus 39.6%; P = 0.02). CA15-3 increased greater than or equal to 25% more often than CEA in patients with PD (75.0 versus 58.3%) and decreased greater than or equal to 25% more often than CEA in patients with RD (38.1 versus 23.8%). In a logistic regression model, changes in CA15-3 levels correlated significantly with both PD (P = 0.0004) and RD (P = 0.02), while changes in CEA levels did not (PD, P = 0.34; RD, P = 0.92). Furthermore, correlations obtained when using both antigens together failed to improve the results obtained with CA15-3 alone. The present study thus demonstrates that CA15-3 is more useful than CEA in monitoring the clinical course of patients with metastatic breast cancer.