Dong, Vadla et al. find that oncogenic Ras and p53 cooperatively stimulate JAK/STAT cytokines to promote non-autonomous tissue overgrowth in Drosophila. Further, blocking STAT signalling prevents the growth-inducing effect of p53 overexpression and ionising irradiation in human cancer lines in culture and in mouse xenografts, suggesting a therapeutic route. This evidence concerns the gene TP53 and cancer.