In HER2-positive BT-474 breast cancer cells, for example, the expression of HER2/cytokeratin/Hoechst was examined first by triple IF followed by Pap staining (or Pap → IF), and the results confirmed the HER2 positivity of cytokeratin-positive BT-474 cells (Fig. 3A). This evidence concerns the gene ERBB2 and breast cancer.