In ALL, direct or indirect activation of the p53 pathway was observed after treatment with the demethylating reagent 5-aza-2′-deoxycitidine, and was accompanied by an increase in apoptosis [73] and in breast cancer, telomere shortening was correlated with a different level of hypermethylation of TP53 [83]. The gene discussed is TP53; the disease is acute lymphoblastic leukemia.