Preliminary control experiments using lymphoma cells from Myc/+;Rosa26-CreERT2/+;Phgdh+/+ mice showed no overt evidence of Cre toxicity (Supplemental Figure 9), but they did show different lymphoma genicity, probably reflecting different cooperating mutations that had evolved to counterbalance the proapoptotic activity caused by enforced Myc expression (49). The gene discussed is PHGDH; the disease is lymphoma.