MDM2 and lymphoma: Two, perhaps three, other FoxO3−/−Eμ-myc lymphomas lacking p53 expression had elevated Mdm2 but did not express p19Arf (#124, #240 and perhaps #94), suggestive of p19Arf deletion, as observed previously.51 Thus, overall, 5 or 6 of 13 (38–46%) FoxO3−/−Eμ-myc lymphomas analysed showed evidence of loss of p53 or Arf function, comparable to the 13/25 (52%) reported by Eischen et al.51 Thus, the absence of FoxO3 alone appears insufficient to select against inactivation of the p53 pathway.