Correlation of serum levels of CA‐549 to disease status in posttreatment serial samples from breast cancer patients

Abstract CA‐549 is a high molecular weight, circulating marker for breast cancer defined by its reactivity to monoclonal antibody BC4E 549. CA‐549 has recently been shown to be elevated in the sera of 50% of advanced breast cancer patients (n = 80), as compared to <2.0% of benign breast disease patients (n = 79) or healthy individuals (n = 257). The purpose of this study was to evaluate CA‐549 as a tool for monitoring the status of breast cancer disease. Serial serum specimens (n = 381) from a total of 126 metastasis breast cancer patients were prospectively collected over 12 months and tested for CA‐549 levels by immunoradiometric assay. The average percent increase in CA‐549 levels in the 18 patients with disease progression was 115 ± 103% (range = −27% to 440%), with 16 of 18 showing an increase of >25%. CA‐549 levels decreased by a mean of −40.5 ± 22.5% (range = 17% to −75%) in 12 patients with breast cancer regression, with 8 of 12 patients showing a decrease in serum CA‐549 of >25%. For 18 patients diagnosed with clinically stable disease, the mean percent change in CA‐549 was only 20.4 ± 5.7%, range = (−27% to 24%), with 14 of 18 having changed by <25%. For patients with no evidence of disease, 75 of 78 were CA‐549 negative throughout the study. Three of 78 patients showed borderline positive CA‐549 elevation for at least one specimen. None of these 78 patients showed highly elevated CA‐549. This study confirms the highly specific nature of CA‐549 as a breast cancer marker, and indicates that changes in CA‐549 levels are associated with the clinical course of the disease. Thus this test may be a useful tool to monitor response to treatment and recurrence of breast cancer.