To address this issue, we directly compared the bindings of the aptamer to either the HER2-positive (SK-BR-3), or the HER2-negative breast cancer cells (MDA-MB-231 and MCF-7) [23]under the same experimental conditions. The HER2 expressions in these breast cancer cell lines had been extensively analyzed by prior studies with mRNA or Western assays [24-27]. Here, ERBB2 is linked to breast cancer.