Rras2(Q72L)fl/fl xmb1-Cre mice do not develop any detectable malignancy, whereas mice that express the Rras2(Q72L) mutant in all tissues (tamoxifen-regulated Cre-ERT2-regulated mouse strain [iCre-Rras2Q72L]) do develop a form of T-cell acute lymphoblastic leukemia (T-ALL) in 100% of mice, but not CLL (Fernandez-Pisonero et al., under revision). The gene discussed is RRAS2; the disease is acute lymphoblastic leukemia.