Loss of one bcl-x allele significantly delays Εμ-myc lymphoma development. Kaplan-Meier analysis of tumor development comparing control Εμ-myc transgenic mice with Εμ-myc/bcl-2^+/− and Εμ-myc/bcl-x^+/− mice. Median tumor onset was 116 days for Εμ-myc, 154 days for Εμ-myc/bcl-2^+/− (P = .303) and 174 days for Εμ-myc/bcl-x^+/− mice (P = .023).