PAK4 and breast cancer: Guided by transcriptome analyzes, mass spectrometry and computational modeling, we also identified a new PAK4-mediated signaling pathway that controls senescence in breast cancer (Figure 1(b)).1 The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) subunit RELB was functionally required for the growth arrest observed upon PAK4 inhibition.