Although Eμ-myc mice generally succumb to sIgM−B220+ pre-B lymphomas or sIgM+B220+ B-cell lymphomas,33, 34 certain crosses have led to changes in tumour phenotype, either predominantly B-cell lymphomas (e.g., in p53+/−/Eμ-myc and vavP-Mcl-1/Eμ-myc mice),35, 36 or a complete change in immunophenotype (e.g., in Eμ-bcl-2/ Eμ-myc and Eμ-v-abl/ Eμ-myc mice).37, 38 However, immunophenotyping of the FoxO3−/−Eμ-myc lymphomas revealed no major difference in the proportion of pre-B versus B-cell tumours compared with Eμ-myc lymphomas (Figure 2d). This evidence concerns the gene PTPRC and lymphoma.