ERBB2 and breast cancer: The effect of selumetinib on ErbB2 was not unique to MCF-ErbB2 cells as we found that the Mek inhibitor downregulates ErbB2 in detached ErbB2-positive human breast cancer cell lines BT-474, AU-565 and HCC-1419 [31, 32] but has no effect on ErbB2 levels when these cells are attached to the ECM (Figure 1B-1D).