Gene inactivation in leukemia is largely mediated by promoter’s hypermethylationof gene involving in cellular functions such as cell cycle, apoptosis, and gene transcription.Inactivated genes, such as ASPP1, TP53, IKZF1 and P15, may correlate with poor prognosis in acute lymphoid leukemia (ALL), chronic lymphoid leukemia (CLL), chronic myelogenousleukemia (CML) and acute myeloid leukemia (AML), respectively. The gene discussed is TP53; the disease is lymphoid leukemia.