PS997 A NEW BIOMARKER OF RESPONSE TO 5‐AZACITIDINE THERAPY IN MDS AND AML PATIENTS: SIRPB1

Background: Myelodisplastic syndromes (MDS) and Acute Myeloid Leukemia (AML) are a group of diseases of the elderly that initiates in a hematopoietic stem cell and are characterized by clonal hematopoiesis and uncertain prognosis, mostly due to cytogenetic background. In both diseases, 5‐Azacitidine (5‐Aza) has been successful, inducing prolonged survival and delayed AML evolution. Aims: To identify the genes mostly predictive of treatment response, we use high‐throughput genomic analysis (SNP arrays and/or NGS‐RNA‐seq and/or NGS‐WES and/or GEP) in azacitidine‐sensitive and resistant MDS/AML patients. Methods: NGS‐WES or RNA seq HiSeq 2000 (Illumina) was positively done in 35/214 AML samples (16%), GEP (GeneChip Human Transcriptome Array 2.0, Affymetrix Inc.) was performed in 65/214 AML samples (30%). SNPs arrays (CytoScan HD Array, Affymetrix Inc.) in 125/214 AML samples (58%) and 18/32 MDS samples (56%) at diagnosis, then analyzed by Chromosome Analysis Suite (ChAS) v1.2 (Affymetrix Inc.), Nexus Copy Number™ v7.5 (BioDiscovery) and GeneGo MetaCore™ software. Results: We treated 246 adult pts with MDS or AML: 214 were AML and 32 were MDS with a median age of 59 and 70 years, respectively. 45 were treated with 5‐Aza (32 MDS/13 AML), while 201 AML with conventional chemotherapy. 45 MDS/AML were treated with at least one complete cycle of 5‐Aza (75 mg/sqm/daily). SNP arrays was done in 22/45 (49%), 13 pts were defined “insensitive/resistant”, ie. never achieving clinical complete remission (CCR) and 9 were defined “sensitive”, ie. all of them obtaining CCR. Copy Number Alterations (CNAs) ranged from loss or gain of complete chr arms to focal deletions and gains targeting one or few genes involving macroscopic (>1.5 Mbps), submicroscopic genomic intervals (50 Kbps‐1.5 Mbps) and LOH (>5 Mbps) events. Macroscopic CNAs affecting a complete chromosome or its arms were detected in 5 of 22 pts (23%), while classical cytogenetic was able to detect only two cases of trisomy 8 (9%), suggesting superiority of SNPs array for CNAs identifications. Microscopic CNAs abnormalities were detected in all of the patients affecting all the chromosomes. Chromosomic aberrations disease‐related are more statistically frequent on pts “insensitive” versus pts. “sensitive” (64% vs. 35%) ( p ≤0.01). Moreover we found that from the median of chromosomic alterations lenghts (in kbp) the group of “insensitive” MDS/AML patients to 5‐Aza present more gains and losses than “sensitive” ones. By Nexus Copy Number software, we identify 137 genes highly differentially gain (SIRPB1 and KIT with p ≤ 0.05) or loss (SIRPB1, LCE1C, BCAS1, EXD3 with p ≤ 0.05) or LOH between “insensitive” versus “sensitive” to 5‐Aza ( p ≤ 0.05). Among these, we focused on SIRPB1 (cytoband 20p13, 56Kbps), since it was loss on 14/22 (64%) “insensitive” pts ( p  = 0,023) and gain on 7/22 (70%) “sensitive” ones with a significantly ( p  = 0,0324), respectively. SIRPB1 common deletion region goes from 1571 to 1598 (27 kbps) and common amplified region goes from 1561 to 1591 (30 kbps). By NGS‐WES we analyzed 35/214 (16%) AML samples at diagnosis, finding mutations in SF3B1, NPM1, CBL, RUNX1, BCOR, KIT, GATA2, IDH2, KDM6A, KIAA1324L, PRIM2, RRN3, APOBR and again in SIRPB1 an heterozigosity frameshift deletion (c. 388delC; p. H130fs) in exone 2 in a AML pts with normal karyotype. By GEP we further analyzed 48/214 (22%) AML samples for SIRPB1 in order to correlate and confirm the expression or loss of expression of these genes, in correlation with 5‐Aza response. Summary/Conclusion: We conclude that SIRPB1 is a promising marker of response to 5‐Aza treatment in MDS and AML.