In a study of 76 patients with MBC from Munzone et al. [60], those with HER2+ CTCs at baseline after HER2- primary breast cancer had significantly shorter PFS than those who retained HER2− status on CTCs, and patients with no CTCs (15 weeks vs. 20 weeks vs. 25 weeks, for HER2+ CTCs, HER2− CTCs, and no CTCs, respectively) [60]. This evidence concerns the gene ERBB2 and breast cancer.