TP53 and neoplasm: Interestingly, we observed a greater frequency of all-green PanINs (Fig. 7b), suggesting that p53 loss promoted pancreatic tumour initiation by oncogenic Kras. We also evaluated the role of p53 on cell expansion in low-grade tumours by analysing the proportion of incompletely labelled low-grade PanINs (G2-X recombination occurring after tumour initiation) containing predominantly green or red cells (Fig. 7c).