Blocking STAT3 S727 phosphorylation significantly increases the life of K-RasG12D animals. Kaplan-Meier survival curves of animals of the indicated genotypes. Control animals (Mx:F/+) and Mx:STAT3F/SA (Mx:F/SA) animals survived until the experiment was terminated at over 300 days. Mx:K-Ras:F/+ (Mx:K:F/+) mice died rapidly from MPNs with a median survival of 83 days. Mx:K-Ras:F/SA (Mx:K:F/SA) animals survived significantly longer (***P < .001 log-rank test) with a median survival of 115 days. Cohorts included at least 10 animals, except Mx:F/SA (5 animals).