Pathway analysis of patients for whom induction failed in COG study 9404. The analysis shows arrest at G₀/G₁, suggesting that affected cells are not proliferating rapidly, thus conferring an inherent resistance to the cell-cycle therapies that are given during induction therapy. In these patient samples, subsequent analysis also showed an up-regulation of the MDR1 and MRP1 genes, which code for P-glycoproteins that are well known to confer chemoresistance in a variety of hematological malignancies. (Used with permission from Winter et al.²⁶ )