Thus, we measured, with the ELISA method, the human blood concentrations of five major HER ligands: EGF, transforming growth factor alpha (TGFa), neuregulin (NRG), heparin-binding EGF-like growth factor (HB-EGF) and epiregulin in the samples of healthy donors and HER2+ BC patients used in clonogenicity assays. The gene discussed is ERBB2; the disease is breast cancer.