To select HER2-positive and negative breast cancer cell lines, we determined the HER2 status of the breast cancer cells in terms of genomic amplification and the mRNA expression of HER2. Figure 1A and 1B show the genome copy number in the HER2 locus and the mRNA expression levels of HER2 gene assessed by quantitative PCR, respectively. The gene discussed is ERBB2; the disease is breast cancer.