P343: mutations in genes related to epigenetic regulation, treatment resistance and ikzf1 plus profile identify relapse profiles in b-all.

Background: B acute lymphoblastic leukemia (B-ALL) is a malignant hematological neoplasm characterized by high genetic heterogeneity. Although survival rates have increased in recent decades, largely due to current treatment regimens, approximately 20% of children and 40-50% of adults with B-ALL relapse with poor post-relapse long-term overall survival rates ranging from 15 to 50%. Despite the above, few studies focusing on the analysis of the genetic changes driving the relapse have been reported, being particularly relevant to identify new biomarkers that can help in the prognosis and treatment of patients with relapsed B-ALL. Aims: To identify genetic lesions driving relapse in patients with B-ALL, based on the mutational landscape present at diagnosis in order to adjust therapy to the genetic profile of each patient. Methods: Paired samples (diagnosis-relapse) of 40 B-ALL patients (10 children and 30 adults) were analyzed by massive sequencing, using a personalized panel allowing the detection of single nucleotide variant (SNV), insertions/deletions (INDELs), copy number variations (CNVs), fusions and aneuploidies (Montaño A, et al. J Pers Med. 2020). Results: The most mutated pathway both at diagnosis and at relapse was RAS pathway (18%) while deletions in CDKN2A (40%), IKZF1 (38%) and PAX5 (20%) were the most frequently detected CNVs. In contrast, mutations detected exclusively at relapse were frequently observed in TP53 (15%), ABL1 (13%) and NRAS (10%). The mutational profile at relapse between children and adults was different at both diagnosis and relapse, with a higher enrichment of mutations in the RAS pathway in childhood B-ALL (60% vs 23%). In adults, mutations in genes related to drug resistance: NR3C1 (V271fs), WHSC1 (T1150A), TBL1XR1 (D154fs) and NT5C2 (R238L) were more frequent in very early relapses (<18 months after diagnosis) while mutations related to epigenetic regulation (DNMT3A and IDH2) were associated with late relapses (≥6 months after completing primary therapy) (4% vs 50%). These epigenetic gene mutations have been linked to myeloid neoplasms and associated with a poor prognosis in B-ALL. Most of Philadelphia chromosome positive (Ph+) patients treated with Imatinib had clonal mutations in ABL1 (T315I, E255K or Y253H) at relapse and relapsed earlier than those without ABL1 alterations (80%). Of note, all Ph-like patients with CRLF2r, had an IKZF1plus profile (defined as the presence of IKZF1 deletions that co-occurred with deletions in CDKN2A/B, PAX5, or PAR1 in the absence of ERG deletion) at diagnosis that was maintained at relapse. IKZF1plus profile, has been associated with poor prognosis in patients with B-ALL. We observed two distinct patterns in B-other patients: patients with the IKZF1plus profile without RAS pathway mutations (36%) and patients with RAS pathway mutations in absence of the IKZF1plus profile (45%) which seems to indicate that they are mutually exclusive pathways. Conclusion: Using sequencing technology (NGS) it is possible to identify genetic alterations that are associated with relapse in B-ALL patients. The occurrence of mutations in drug resistance-related genes during therapy is associated with very early relapses while mutations in genes related to epigenetic regulation and the IKZF1plus profile are present from diagnosis and are maintained at relapse in adult patients. This information can be obtained at diagnosis and during treatment to provide personalized treatment. Grants: SACYL(GRS2386/A/21,GRS2385/A/21), JCyL SA118P20, IBSAL-Herencia JS Escudero IBPED21/00001, FMM21/002 AP176752021, Pfizer GM Grants 69383919.Keywords: Relapsed acute lymphoblastic leukemia, Molecular cytogenetics, B cell acute lymphoblastic leukemia