TP53 and neoplasm: By generating Eμ‐myc; Pot1b∆/∆; p53P/+ mice compromised in the induction of p53‐dependent apoptosis and Eμ‐myc; Pot1b∆/∆; p21−/− mice unable to initiate p53‐dependent cellular senescence, we are able to directly compare the tumor suppressive contributions of p53‐mediated apoptosis vs. cellular senescence.