To determine whether loss of a single FoxO can cooperate in Myc-driven tumorigenesis, we crossed FoxO3−/− mice21 with vavP-MYC10 mice, which express the transgene in all haemopoietic lineages and primarily develop myeloid tumours with some T lymphomas,31, 32 and with Eμ-myc mice, which constitutively express Myc in B lymphoid cells and are susceptible to pre-B and B lymphomas.33, 34. This evidence concerns the gene MYC and lymphoma.