ERBB2 and breast cancer: SK-OV-3 human ovarian cancer cells and MDA-MB-468 human BC cells were chosen to establish tumors that homogeneously or heterogeneously expressed HER2 and EGFR since SK-OV-3 cells are HER2-positive but have negligible EGFR expression20 while MDA-MB-468 cells are EGFR-positive but have negligible HER221 (Figure 1).