Abstract
CA 15–3 (also known as MUC1) is the most widely used serum marker in breast cancer. MUC1 is a large transmembrane glycoprotein which is frequently overexpressed and aberrantly glycosylated in cancer. Physiologically, MUC1 appears to play a role in cell adhesion and the high levels present in cancer may be causally involved in metastasis. At present the main uses of CA 15–3 are in preclinically detecting recurrent breast cancer and monitoring the treatment of patients with advanced breast cancer. In a prospective study of 368 patients we show that patients with high preoperative levels of CA 15–3 (>30.4 U/mL) had a worse outcome than patients with low levels of the marker. In multivariate analysis CA 15–3 as a prognostic marker was independent of both tumor size and nodal status. Furthermore, in multivariate analysis the prognostic impact of CA 15–3 was stronger than that of tumor size and at least as strong as nodal status. CA 15–3 may thus be the first independent prognostic serum marker in breast cancer.