Although it remains unclear if our findings are related to the previously reported prognostic roles of high EGFR (68, 69) and Her2 (70) in the serum of patients with breast cancers, EGFR/ErbB2 has been detected in CTCs consistently during serial blood draws (71) and was found to be activated (as determined by the presence of its phosphorylated state (72) in CTCs) with increasing frequency often during MBC progression (72). Here, EGFR is linked to breast cancer.