Aside from clinical data showing the correlation of high MED1 levels with poor outcome and disease-free survival of patients undergoing anti-estrogen therapies (Ross-Innes et al., 2012; Nagalingam et al., 2012), a recently published prominent study also discovered an increased frequency of MED1 mutation in circulating tumor cells (CTCs) in breast cancer patients following anti-estrogen and anti-HER2 treatments (Murtaza et al., 2013). Here, MED1 is linked to breast cancer.