ERBB2 and breast cancer: After 1-h treatment of HER2-positive breast cancer cell lines with 25 μg/mL (1.9 μM), AlexaFluor 488-conjugated HER2-binding Affimers showed a clear association, with both the membrane and the cytosol demonstrating internalization, whereas no association or internalization was seen in the HER2-negative MDA-MB-231 cells (Figure 2A and 2B).