KRAS and leukemia: We further show that pre-leukemia cells display higher viability, but not proliferation, than healthy B cell precursors and eventually transform, likely by the accumulation of mutations (e.g. Kras Q61H) that tend to contribute to increased IL-7R-mediated signaling and proliferation, into full-blown leukemia with characteristics of PAX5 P80R or Ph-like ALL.