ERBB2 and neoplasm: Loss of PAK1 prolonged survival and showed loss of β-catenin in the MMTV-HER2 transgenic mice; when treated with small-molecule inhibitors of PAK or β-catenin, it showed tumor regression; and combined inhibition was synergistic in mice bearing xenografts of HER2-positive breast cancer cells (Arias-Romero et al., 2013).