Pak1 over-expression predicts responsiveness to Mek inhibitors. Each pair of boxplots represents the average GI50 for luminal cell lines that over-express Pak1 (Pak1-high, blue) and those that express it at normal levels (Pak1-low, red). Within each box, the line represents the median; upper and lower boundaries represent the first and third quartiles, respectively. The vertical lines extend to +/- 1.5 IQR. For all three drugs, Pak1-high cell lines are significantly more sensitive than Pak1-low cell lines.