To counteract this apoptosis, the majority of BL cell lines and around 30% of BL tumours carry TP53 mutations, while BL tumours that retain wild-type p53 carry mutations or epigenetic changes that lead to aberrant expression of the p53 regulator proteins, p19/ARF and MDM2 [23]. The gene discussed is CDKN2A; the disease is Burkitt lymphoma.