ERBB2 and breast carcinoma: However, in HER-2 overexpressing breast cancer, PI3K signaling inhibition leads to increased HER-2-mediated ERK activation, pointing to yet another important growth-promoting signaling axis, the Ras-Raf-MEK-ERK pathway (Fig. 2), and the potential need for adding for instance MEK inhibitors in certain patient subgroups (Serra et al. 2011).