Eμ-myc–induced lymphoma expressing high levels of BCL-2 evolve later than lymphomas with a disrupted p53 pathway. (A) Immunoblot of primary tumors found in a population of Eμ-myc mice (n = 23). Early and late indicate mice that survived shorter or longer than 75 days, respectively. Squares are highlighting protein alterations associated with respective second hit. Splenocytes from wild-type mice were used as control (lane C). (B) Kaplan-Meier plot of mice from before mentioned population subdivided into 2 groups on the basis of the observed second hit (P_{BCL-2 vs p53} = .0183; n_BCL-2 = 7; n_p53 = 6). (C) All lymphomas (n = 23) were analyzed by FACS for the presence of surface IgM (sIgM). Dot blots show 2 representative tumors from each subpopulation (early lymphomas: #1 and #2; late lymphomas: #3 and #4). Numbers indicate percentages of sIgM⁺ B cells. (D) Kaplan-Meier plot of mice that received a transplant with primary tumor cells obtained from diseased Eμ-myc mice. (sIgM⁻, n = 17; sIgM⁺, n = 15). Mice receiving sIgM⁺ tumor cells show significant longer survival time than mice that received a transplant with cells negative for IgM surface expression (P_{sIgM−vs sIgM+} < .001).