In the present study we used PLA to study the dimerization pattern of HER protein family members after treatment of MCF-7 (not HER-2 amplified) and SKBR3 (HER-2 amplified) human breast cancer cells with or without HRG1 and various HER-2 / HER-3 blocking agents (trastuzumab, pertuzumab and U3-1287). The gene discussed is ERBB2; the disease is breast cancer.