MUC1 and breast cancer: The measurement of circulating MUC1 levels in the serum, as determined by the CA15–3 assay (approved by the US Food and Drug Administration), has been used to monitor the clinical course of patients with breast cancer during treatment and to detect early disease recurrence; and the elevated levels of serum MUC1 are always linked with poor survival (Kufe, 2009; Singh & Bandyopadhyay, 2007).