The combined expression of BCL2 with MYC induced leukemia in vivo with a penetrance similar to that with the MYC/HOXA9 combination (Figures 4E and 6B, and Figure 6—figure supplement 1A), in accord with previous reports (Beverly and Varmus, 2009; Luo et al., 2005). Here, HOXA9 is linked to leukemia.