Survival curves of WT and Egr1-deficient mice after ENU treatment. (A) 4 weeks of age. (B) 20 weeks of age. Egr1^+/− and Egr1^−/− mice developed T-cell lymphomas or MPD at a significantly increased rate and frequency compared with WT littermates. **Only 1 mouse from the WT cohort treated at 20 weeks developed a malignant disease (lymphoma). Two mice from this cohort were killed due to severe dermatitis. (Note that dermatitis is a common phenotype in C57BL/6 mice, and we observed no differences in the incidence or severity of dermatitis in WT versus Egr1-deficient mice, nor in healthy mice versus mice with lymphoma or MPD.)