MYC levels determine the types of hematopoietic neoplasms that develop in mice carrying 1 or 2 copies of the same Vav-driven MYC transgene. Heterozygous MYC transgenic mice are prone to late-onset monocytic neoplasms (blue box), whereas homozygous MYC transgenic mice, which express twice as much MYC (2 × MYC) as their heterozygous counterparts do (1 × MYC), develop early-onset T-cell lymphomas (yellow box). HSC indicates hematopoietic stem cell; CMLP, common myelolymphoid progenitor; and CLP, common lymphoid progenitor.