In a recent study, one of the most popular serum biomarkers for the follow up of breast cancers and the early detection of breast cancer metastases is the cancer antigen Ca15.3, (Wang et al. 2005; Mathelin et al. 2006), a carbohydrate antigen commonly known as a “mucin,” which influences cell–cell interaction and cell growth (Banfi et al. 1997). Here, MUC5AC is linked to breast cancer.