ERBB4 and lung cancer: Similarly, in lung cancer, HER4 DDMs were reported to induce receptor switching from HER4:HER4 homodimer to HER4:HER2 heterodimer.21 While HER2:HER2 homodimer activates MAPK signaling in the absence of ligands, HER3 preferably forms heterodimer with HER2 in the presence of Neuregulin (NRG-1) and NRG-2, but possesses impaired kinase activity.2,22 However, phosphorylation by HER2 triggers oncogenic signaling via PI3K/AKT pathway.12,23–25