A) Tumor volumes in mice (number indicated) injected (subcutaneously) with CreERT2 expressing Mdm2fl/flp53-null lymphoma cells and administered tamoxifen (Tam) or vehicle control (corn oil, Oil) starting day 15 were measured (*p<0.0006). B) Kaplan-Meier survival curves of the mice in A (p<0.0001). Arrow indicates the day tamoxifen or oil administration began. C–E) Annexin-V (C), sub-G1 DNA (D), and cells in G2/M (E) measured in extracted lymphoma cells 48hrs after tamoxifen or vehicle control administration to mice. For C and D, representative data, left; mean values, right. C, *p=0.006; D, *p=0.0008; E, *p=0.013. F, G) Western blots of lymphomas harvested after 48hrs (F) or at humane endpoints (G) following tamoxifen (Tam) or vehicle control (Oil) administration. For G, a lymphoma harvested 48hrs after tamoxifen administration (Tam 48) included for comparison.