In transgenic mouse models of RET-rearranged thyroid cancer, RET transgene copy number has been correlated with disease severity (Knostman et al., 2007), tumor onset has ranged from weeks to months, metastasis is uncommon (<10% on RET/PTC3), and metastasis is modestly enhanced on a p53 mutant background. Here, TP53 is linked to thyroid cancer.