ART4 and breast cancer: Therefore, the identification of glycoprotein levels has intensified since the expression of these substances can provide direct information on the evolution of pathological conditions and the physiological state.1,2 CA 15-3, a glycoprotein of approximately 400 kDa like mucin 1 (MUC1), is secreted by breast cancer cells and is the most commonly used serum biomarker for monitoring breast cancer.3