MCM2 and neoplasm: Similarly, MCM2 deficient (Mcm2IRES-CreERT2/ IRES-CreERT2) mice exhibit near to 100% penetrance of T-lymphocytic leukemia (TLL) within 5 months on the 129Sv background on which they were constructed [5] but a broader spectrum of tumor types with more variable latencies in a mixed 129Sv/BALB/c genetic background [8].