We obtained support for such tumor-promoting effect of p53 ablation in an Rb-/-Rbl2-/- teratoma model: tumor size was inversely correlated with the level of DNA breaks and Rb-/-Rbl2-/-p53-/- teratomas generally showed lower levels of DNA breaks than Rb-/-Rbl2-/- teratomas. The gene discussed is RB1; the disease is teratoma.