Mechanisms of relapse in acute leukaemia: involvement of p53 mutated subclones in disease progression in acute lymphoblastic leukaemia

Mutations of the p53 tumour suppressor gene are infrequent at presentation of both acute myeloblastic leukaemia (AML) and acute lymphoblastic leukaemi a (ALL), being found in between 5-10% of AML and 2-3% of ALL. Here we have studied the frequency of detection of p53 mutations at relapse of both AML and B-precursor ALL. In those patients with detectable mutations at relapse we investigated whether the mutation was detectable at presentation and wa s thus an early initiating event or whether it had arisen as a late event a ssociated with relapse. Bone marrow samples from 55 adults and children wit h relapsed AML (n = 41) or ALL (n = 14) were analysed for p53 gene alterati ons by direct sequencing of exons 5-9. For samples where a p53 mutation was found at relapse, analysis of presentation samples was carried out by dire ct sequencing of the exon involved, or by allele-specific polymerase chain reaction (PCR) if the mutation could not be detected using direct sequencin g. A p53 mutated gene was found at relapse in seven out of 55 cases. The fr equency was higher in relapsed ALL (four out of 14 cases; 28.6%) compared t o AML (three out of 41 cases; 7.3%). In five out of the seven cases present ation samples were available to study for the presence of the mutation. In two out of two AML patients the p53 mutation was detectable in the presenta tion sample by direct sequencing. In three ALL patients analysis of present ation material by direct sequencing showed a small mutant peak in one case, the other two being negative despite the sample analysed containing > 90% blast cells. However in both of these patients, the presence of p53 mutatio n was confirmed in the presentation sample using allele-specific PCR. In on e of these patients the emergence of a subclone at relapse was confirmed by clonality analysis using IgH fingerprinting. Our results confirm that in A LL p53 mutations are present in a proportion of patients at relapse. Furthe rmore cells carrying the mutation are detectable at presentation in a minor clone suggesting that p53 mutations in ALL may be a mechanism contributing to disease relapse.