TP53 mutations in adult acute lymphoblastic leukemia (ALL) are relatively frequent in molecularly negative case of both B- and T-lineage and correlate with poor response to induction therapy

Background. TP53 mutations occur in several cancers including hematologic malignancies, particularly chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML), where the incidence is of 5-10% and 7%, respective- ly. While in these neoplasms TP53 mutations have been widely investigated and correlate with a poor prognosis, their incidence and role in acute lymphoblastic leukemia (ALL) remain controversial. Aims. To investigate the incidence of TP53 mutations and their correlation with known molecular aberrations and outcome, we analyzed a cohort of 98 newly diagnosed adults with ALL. In 10 cases, we also analyzed paired relapse samples. Methods. Genomic DNA was extracted from mononuclear cells of patients enrolled in different GIMEMA protocols. All samples contained at least 70% of leukemic blasts. In 10 cases paired diagnosis-relapse material was analyzed. Sixty-two patients had a B-lin- eage ALL (B-ALL) and 36 a T-ALL. Molecular screening showed that, within B- ALL cases, 25 harbored the BCR/ABL, 9 the ALL1/AF4 and 4 the E2A/PBX transcripts. The remaining patients were negative for the presence of the aforemen- tioned fusion genes. Within T-ALL, 4 cases harbored the SIL/TAL1, 1 NUP98/RAP1GDS1 and 1 SET/NUP214 rearrangement.TP53 mutation analysis was performed using a microarray-based sequencing assay, the AmpliChip p53 Research Test (Roche Molecular Systems), which allows sequencing of the entire coding region of the TP53 gene, including exons 2-11 splice sites. Results were validated by direct sequencing. Results. The AmpliChip p53 assay iden- tified TP53 missense mutations in 8 patients (8.16%) studied at diagnosis. Within the mutated patients, 4 had a B-ALL (6.4%): 3 cases (12.5%) had no known molecular abnormality and 1 harbored the BCR/ABL rearrangement (4%). No mutations were found in E2A/PBX1+ and ALL1/AF4+ cases. Within the T-ALL group, 4/36 carried TP53 mutations (11.1%): none of these cases har- bored known molecular aberrations. Overall, TP53 mutations were found in 13% of ALL cases without known molecular abnormalities.Sanger sequencing confirmed all the mutations but one, suggesting the presence of a sub-clonal population. Furthermore, of the 10 paired patients studied, 2 acquired the mutation at relapse (20%): one patient had a BCR/ABL+ B-ALL and the other a T- ALL. Patients harboring TP53 mutations were predominantly males (M/F= 6/2) and were younger than TP53 wild-type (wt) cases (TP53 mut 30 vs TP53 wt 36.5 years). Since the majority of the mutations occurred in molecularly negative patients, response to induction was evaluated in this subset: of the 47 evaluable patients, 12 were refractory to induction and, remarkably, 25% were TP53 mutated. Conclusions. These results indicate that TP53 mutations frequency in ALL at the onset of the disease is similar to that reported in CLL and AML. Furthermore, they indicate that, within patients without known molecular aberrations of both T- and B-lineage, TP53 alterations can be detected in 13% of cases and therefore could be particularly useful for the prognostic stratification of these subgroups. Indeed, although statistical significance was not reached because of the small number of TP53 mutated patients, our results indicate that TP53 mutations have a deep impact on response to induction treatment and achievement of complete remission.