To elucidate the molecular consequences of p53 activation upon Nutlin-3a exposure in ALL cells and to identify novel potential biomarkers of clinical activity, we performed gene expression profile analysis of the Nutlin-3a sensitive cell lines BV-173 and SUP-B15 after 24 hours of drug exposure and compared them with DMSO-treated cells (DMSO 0.1%). This evidence concerns the gene TP53 and acute lymphoblastic leukemia.