Using a HER3 mutant lacking ECD ligand binding activity, we observe that tumor growth is not diminished (Figure 7A) and sensitivity to lapatinib is not increased (Figures 7E and 7F) by eliminating ligand binding, and it is evident that in vitro studies of ligand administration have overestimated the role of ligand stimulation in vivo. Here, ERBB3 is linked to neoplasm.