ROLE OF TP53 MUTATIONS IN REFINING PROGNOSIS OF KTM2A-REARRANGED ADULT B-LINEAGE ACUTE LYMPHOBLASTIC LEUKEMIA PATIENTS

Background: In B-lineage acute lymphoblastic leukemia (B-ALL), 5-10% of adult cases show KTM2A rearrangements (KMT2A-r) with few secondary alterations, pointing to its initiating role. Over the past two decades, the use of intensive and measurable residual disease (MRD)-driven treatments has yielded significant outcome improvements. Nonetheless, KMT2A-r ALL patients still display a poor outcome. Aims: To evaluate the role of additional genomic aberrations in refining prognosis of KTM2A-r ALL, we focused on TP53 aberrations and correlated them with MRD levels and outcome. Methods: Between 2015 and 2024, 292 newly diagnosed Philadelphia-negative B-ALL patients aged 18-65 years were treated with the GIMEMA LAL1913 (or accordingly) and GIMEMA LAL2317 protocols. The cohort included 27 (9%) KTM2A-r cases. TP53 mutations screening was performed with the TP53 OncoKitDX in 25 cases (in 2 material was not available). For MRD, KTM2A::AFF1 transcript levels were monitored by RQ-PCR, while the Invivoscribe LymphoTrack® Dx NGS assay was used to detect clonal IG/TR rearrangements. Results: KMT2A-r cases (27) showed a higher median age (46.5 vs 40.1 years) and a higher median white blood cell count (64x109/l vs 26x109/l, p<0.01) compared to the other Ph- B-ALLs. All KTM2A-r cases had CD10- pro-B ALL and carried the t(4;11)(q21;23) translocation, resulting in the KTM2A::AFF1 gene fusion. A single TP53 deleterious mutation - clonal in 2 (p. R273H and p. R282G) and subclonal in 5 - was detected in 7 patients (28%), while 2 (both clonal, p. R282W and p. R158H) and 3 mutations (1 clonal p. N288D and 2 subclonal) were detected in 1 patient each (4%). A TP53 P72R polymorphism was frequently found (16/25, 64%). One of the 2 refractory cases and 2 of the 6 relapsed patients carried a clonal TP53 mutation. One patient who died in induction also had a TP53 clonal mutation. MRD evaluation by KTM2A::AFF1 showed a MRD positivity at timepoint 1 (TP1) in 6/6 (100%) TP53 mutated patients. Similarly, at TP2 3/5 (60%) TP53 mutated patients were still MRD+ and 1 was positive-not-quantifiable (2 were not evaluable for lack of material). Contrariwise, in the cohort of KTM2A::AFF1 TP53 wildtype patients, 6/12 (50%) were MRD+ at TP1, and only 4/11 (35%) remained MRD+ also at TP2. The difference in MRD response between TP53 mutated and TP53 unmutated cases was significant (p<0.01). IG/TR gene screening, carried out for future MRD dual marker monitoring, was performed in 20 cases: 17 (85%) had at least 1 clonal sequence, while in 3 (15%) no marker was identified. Gene family analysis revealed an enrichment of VH6 in KTM2A-r patients (75% of cases). Summary/Conclusion: Though limited by the small numbers, clonal TP53 mutations are often detected in KTM2A-r B-ALL cases and are associated with KMT2A MRD persistence and poor outcome. Notably, in KTMT2A-r cases there was an enrichment in the VH6 family, detected virtually only in this subset and at variance from other ALL cases; further studies are ongoing to clarify if this enrichment is linked to the KTM2A-r or to the immature differentiation stage of the leukemic cells. Future goals include investigating the role of TP53 in sustaining refractoriness and relapse and evaluating the role of additional copy number aberrations (namely IKZF1) in risk stratification. Furthermore, through the identification of patient-specific IG/TR gene rearrangements, IG/TR MRD is also being analyzed and will be compared with the KTM2A::AFF1 transcript levels and outcome.