Clinical value of CA 15-3 for detection of distant metastases in newly diagnosed breast cancer.

The aim of the study is to investigate the clinical value of CA 15-3 for detection of distant metastases (DM) in newly diagnosed breast cancer. This retrospective study focuses on a population of 1,007 patients with locally advanced breast cancer (n=561) or metastatic breast cancer (n=446) diagnosed at the CGFL (Centre Georges Francois Leclerc) from March 1998 to October 2013. These patients underwent a measurement of CA 15-3 and an assessment of extension before any treatment. The cut-off value of CA 15-3 was determined and verified on two independents subpopulations determined in drawing lots. The ROC curve shows an AUC of 0.85 (p<0.0001). At the threshold of 50 kU/L, CA 15-3 before treatment has a predictive value on the existence of DM independently of the other prognostics factors. This predictive value has been found in every molecular subtype (AUC≥ 0.70; p≤ 0,085). The rate of false negative is of 38% and depends on the number and the type of the metastatic localization. Among the 28 patients without DM and a CA 15-3> 50 kU/L, 13 have developed DM and 11 died of cancer. In conclusion, these facts confirm the independently predictive value of CA 15-3 before treatment on the existence of DM and the complementarity of the marker with the assessment of extension by imagery.