High levels of mRNA encoding mammaglobin, CK-19 (keratin 19) (Silva et al., 2001) and HER2/neu (Erb-B2 receptor tyrosine kinase 2) (Nicolini et al., 2017), which are specific markers of breast cancer (Lianidou et al., 2015), are also found in the blood plasma of patients with given disease. This evidence concerns the gene ERBB2 and breast cancer.