H6PD and cancer: Furthermore, phenotype phase plane done with G6PDH and TKT1 allows us to infer not only that a simultaneous reduction of TKT1 and G6PDH metabolic activity clearly predicts a drop in growth rate but also that, although both branches of PPP can produce r5p, the oxidative branch can be a limiting factor for growth rate in cancer: it means if TKT1 flux is null an increment of G6PDH metabolic activity can produce phenotype, however the opposite situation does not occurs, see Figure 5(E), a hypothesis that needs to be verified with more precise experimental measurements [35].