KRAS and lung cancer: Although lung cancers in LSL-Kras; p53FL/FL mice also responded well to two fractions of 7.3 Gy [factor of 0.96 (SEM – 0.04), n = 14 tumors], this was not statistically different than the response to a single fraction of 11.6 Gy (factor of 1.2, n = 28 tumors, P = 0.23, Figure 3B).