PAK4 and breast cancer: Indeed, we observed a senescence-like response upon PAK4 inhibition in vitro, in vivo and ex vivo using a variety of models (cellular and animal models) and tools (siRNA, CRISPR/Cas9 and small compound inhibition) (Figure 1(a)).1 Upon PAK4 depletion, a panel of breast cancer cells lines showed senescence associated (SA) features including morphological changes, increased SA-β-galactosidase activity combined with inhibited cell proliferation and gene expression changes consistent with a SA-phenotype.