As a result, it has been suggested that P-gp expressionlevels can be used as a predictive biomarker for patients at riskof developing off-target resistance in CML (Figure 1A).9−17 Thus, future treatment options for Philadelphia chromosome positive(Ph+) leukemias would benefit from reduced P-gp-mediated efflux, andthe consequent minimization of potential off-target resistance byP-gp overexpression. This evidence concerns the gene PGP and chronic myelogenous leukemia, BCR-ABL1 positive.