Cytogenetic and molecular predictors of response in patients with myeloid malignancies without del[5q] treated with lenalidomide

<p>Abstract</p> <p>Background</p> <p>While lenalidomide (LEN) shows high efficacy in myelodysplastic syndromes (MDS) with del[5q], responses can be also seen in patients presenting without del[5q]. We hypothesized that improved detection of chromosomal abnormalities with new karyotyping tools may better predict response to LEN.</p> <p>Design and methods</p> <p>We have studied clinical, molecular and cytogenetic features of 42 patients with MDS, myeloproliferative neoplasms (MPN), MDS/MPN overlap syndromes and secondary acute myeloid leukemia (sAML) without del[5q] by metaphase cytogenetics (MC) who underwent therapy with LEN.</p> <p>Results</p> <p>Fluorescence in situ hybridization (FISH) or single nucleotide polymorphism array (SNP-A)-based karyotyping marginally increased the diagnostic yield over MC, detecting 2/42 (4.8%) additional cases with del[5q], one of whom were responded to LEN. Responses were more often observed in patients with a normal karyotype by MC (60% vs abnormal MC; 17%, <it>p </it>= .08) and those with gain of chromosome 8 material by either of all 3 karyotyping methods (83% vs all other chromosomal abnormalities; 44% <it>p </it>= .11). However, 5 out of those 6 patients received combined LEN/AZA therapy and it may also suggest those with gain of chromosome 8 material respond well to AZA. The addition of FISH or SNP-A did not improve the predictive value of normal cytogenetics by MC. Mutational analysis of <it>TET2, UTX, CBL, EZH2, ASXL1, TP53, RAS, IDH1/2</it>, and <it>DNMT-3A </it>was performed on 21 of 41 patients, and revealed 13 mutations in 11 patients, but did not show any molecular markers of responsiveness to LEN.</p> <p>Conclusions</p> <p>Normal karyotype and gain of chromosome 8 material was predictive of response to LEN in non-del[5q] patients with myeloid malignancies.</p

SNP-A Karyotyping Provides Clinically Relevant Results In Myeloid Hematologic Disorders with Unsuccessful Routine Cytogenetic Testing

Abstract Abstract 3374 Metaphase spreads have an established value in the routine diagnostic workup of myeloid malignancies and bone marrow failure disorders. In myelodysplastic syndrome (MDS) abnormal karyotypes play a large role in scoring systems and may greatly impact prognosis, or even predict responsiveness to certain therapies. In aplastic anemia (AA) cytogenetic abnormalities detected by metaphase karyotyping may rule out hypoplastic MDS. In myeloproliferative neoplasia (MPN), an abnormal karyotype may distinguish between reactive or malignant proliferation. Due to technical problems, including specimen quality, viability, hypocellularity or a failure of growth, this routine test may fail to yield conclusive results in some patients. With the advent of SNP-A karyotyping, which only requires extracted DNA, non-informative cases can be resolved. As a cytogenetic test, single nucleotide polymorphism array (SNP-A) analysis can provide an opportunity to improve risk assessment and selection of proper treatment modalities. The advantages of SNP-A include excellent resolution, detection of copy neutral loss of heterozygosity (also known as uniparental disomy or UPD), and perhaps most importantly, the ability to test archived DNA samples, rather than actively dividing cells. However, unlike metaphase cytogenetics, this technology cannot detect subsets of abnormal populations or certain classes of genomic rearrangements, such as balanced translocation, inversion or ring chromosomes. In this study, we examined the prognosis and disease characterization for patients with non-informative cytogenetics (N=144) collected over the last 8 years. SNP-A-based karyotyping has been performed for a representative subset of these patients (N=60) to assess whether this technique could provide clinically relevant information. These patients included patients with MDS (N=20), AA (N=20), AML (N=12) and MDS/MPN (N=3). Bone marrow obtained following induction chemotherapy was excluded. We have detected 27 somatic microdeletions and 33 microduplications (<10Mb) after eliminating germ line copy number variants seen in an internal control cohort (N=1355), publicly available databases or those present in paired non-clonal samples. However, for the purpose of subsequent analysis, somatic microdeletions and duplications were not included, as their prognostic significance has not been validated in large cohorts. (These microalterations may indicate edges of balanced translocations or true clonal pathogenic lesions.) None of these microdeletions were recurrent. Based on these criteria, SNP-A analysis revealed an abnormal karyotype in 14 (23%) patients; 3 with AA and 11 with myeloid disorders. The most common recurrent abnormalities included deletion 5q (N=5) and del7/7q (N=3) but other lesions including13q-, del20, +8p were also seen. Of note we have also detected somatic UPD (regions >25Mb) in 2 cases, including 22q11.23qter and 14q12-q22.1. In 4/60 (7%) a complex karyotype was detected, while 10 had sole lesions (>10Mb). In presumed AA patients, we have identified 2 patients with monosomy 7, prompting a change of diagnosis to MDS and thereby altering their clinical management. In MDS, when cytogenetic prognostic groupings were applied in previously unscored patients, 10/20 had IPSS scores of 3 or greater. The presence of chromosomal abnormalities detected by SNP-At indictated the presence of advanced risk disease and thereby contributed into poorer survival as predicted by IPSS. Disclosures: No relevant conflicts of interest to declare

Germline Events In GFI1 In Myelodysplastic Syndrome

Abstract Germ line mutations in growth factor independent-1 (GFI1) have been described in a small subset of patients (pts) with severe congenital neutropenia. Subsequently, the GFI136N polymorphism, present in 3-5% of controls, has been found overrepresented (11%) in pts with primary (p) acute myeloid leukemia (AML), conveying 1.6 fold risk of development of AML. Mutant GFI136S and N variants lack affinity to HOXA9 (overrepresented in corresponding AML cases), shows increased proliferative potential in vitro and accelerates RAS-driven myeloproliferative neoplasm (MPN) disease in mice. Whole exome next generation (WE NGS) technology facilitates comprehensive screens for the presence of both somatic and germ line genetic alteration. In this study, we used NGS to search for germline variants of the GFI1 gene. We screened 140 pts (mean age 66.8 years, range 44-85) with MDS and related disorders (MDS/MPN and secondary (s) AML) for the presence of GFI1 variants. We found non-synonymous variants in 11 cases (8%), including the previously described pathogenic p.S36N (n=8), p.P107A (n=2), or p.L400F (n=1), while the corresponding frequencies for these alterations were .04 and .001, .002 in the general population. This frequency appears comparable or higher to those previously reported for pAML, but our screen of the TCGA AML cohort, perhaps due to very low coverage for this gene, did not reveal any GFI1 polymorphisms. We next focused on the clinical features of altered GFI1 carriers. A significant proportion of GFI1 cases were younger (age<60 years) 45% (5/11) compared to 19% (p=.05) for wild type (WT) and predominantly male (82% vs. 52%, p=.02). MDS and sAML and MDS/MPN were present in 4, 3 and 4 pts, respectively. Normal cytogenetics at presentation was present in 64% vs. 43% (p=0.22). The availability of the somatic mutational profile allowed us to investigate whether specific genes are more commonly mutated in GFI1 variant cases. Among the 100 most commonly mutated genes, somatic PTPN11 (18% vs. 2%, p=.09), ASXL1 (18% vs. 8% p=0.2), SF3B1 (18% vs. 9%, p=0.3) were the most frequently encountered. Response rate to therapy with hypomethylating agents amongst carriers of GFI1 variants was 50% compared to 35% among WT (p=.32). The mean overall survival of the GFI1mutants was also higher compared to WT (40 vs. 33.6m). In sum, our results demonstrate that potentially pathogenic GFI1 mutations are present in increased frequency in younger pts with MDS and thus may constitute a new predisposing factor for MDS and related myeloid neoplasms. Disclosures: Makishima: AA & MDS international foundation: Research Funding; Scott Hamilton CARES grant: Research Funding. Maciejewski:NIH: Research Funding; Aplastic anemia&MDS International Foundation: Research Funding

Cytogenetic Predictors of Response to Lenalidomide In Myeloid Malignancies without Del(5q)

Abstract Abstract 4016 Lenalidomide (LEN) is effective in patients with myelodysplastic syndromes (MDS) and the del(5q) cytogenetic abnormality, and has activity in a proportion of patients without this chromosomal defect. To date, no clinically actionable biomarkers, other than the presence of del(5q) detected by metaphase cytogenetics, have been identified to predict response to LEN. The diagnostic yield of metaphase cytogenetics can be enhanced by application of fluorescence in situ hybridization (FISH) for targeted chromosomal lesions including del(5q), as this technique is more sensitive. Similarly, single nucleotide polymorphism array (SNP-A)-based karyotyping, due to its superb resolution, allows for detection of previously cryptic unbalanced chromosomal defects. Both techniques can be preformed on interphase cells and thereby do not require cell division. We hypothesized that application of these technologies may allow for better identification of putative responders to LEN in patients with MDS without del(5q); we stipulated that i) we may detect previously unrecognized cases of del(5q) and that ii) more precise analysis of the karyotypes may allow for recognition of other chromosomal markers of response or refractoriness to LEN. In patients with MDS (N=82), MDS/myeloproliferative neoplasm (MPN) (N=13), acute myeloid leukemia (AML) (N=23), and MPN (N=4), the detection rate of del(5q) increased only marginally with use of additional techniques, from 24% (metaphase cytogenetics (MC) + FISH), to 25% (MC + SNP-A), 25% (FISH + SNP-A) and 26% (all 3 methods). Within this cohort, we then analyzed by FISH and SNP-A karyotype a subset of 42 patients with myeloid malignancies without del(5q) by MC who received LEN. This cohort included 33 MDS (RA, N=5; RARS, N=12; RARS-T, N=1; RCMD, N=1; RAEB1, N=4; RAEB2, N=6; MDS-U, N=4), 6 MDS/MPN and MPN patients (CMML1, N=1; CMML2, N=3, IMF; N=2) and 3 secondary AML. By MC, 32 (76%) showed normal karyotype, 1 (2.4%) no growth and 9 (21%) abnormal karyotype other than del(5q). The overall response rate (ORR) (2006 International Working Group criteria) was 44%, including 3 CR, 3 PR and 8 HI. Previously cryptic del(5q) was detected in an additional 1/18 patient by both SNP-A and FISH (secondary AML with normal metaphase cytogenetics), but this case was refractory to LEN. Del(5q) was also revealed by FISH in 1 patient with unsuccessful MC, but, due to the small size of the clone (8%), SNP-A did not detect this lesion. This patient had a sustained PR with transfusion independence. In 28 patients who received LEN for more than 3 months, the ORR to LEN in patients with normal metaphase cytogenetics was 62%, and 17% for those with chromosomal aberrations (p=.08); the addition of SNP-A did not improve the predictive value of normal cytogenetics. We also analyzed 10 patients without del(5q) by MC who received combination therapy with azacitidine (AZA) and LEN, for whom the ORR was 80% (7 CR, 1 PR). By metaphase cytogenetics, 7/10 patients had a normal karyogram and a response of 86%, compared to 3 patients with chromosomal lesions, 1 of whom responded. Similar to the results in LEN alone, inclusion of defects detected by SNP-A or FISH did not allow for better separation of responders based on normal cytogenetics by MC. Six out of 38 LEN-treated patients had a gain of chromosome 8 material by FISH or SNP-A. 4 out of 6 patients had CR (all of them received combination therapy of AZA and LEN), 1 out of 6 had HI, and 1 with complex karyotype had NR (ORR was 83%), while ORR in patients with other chromosomal abnormalities by FISH or SNP-A was 18%. In conclusion, FISH and SNP-A, when added to routine metaphase cytogenetics, marginally increased the diagnostic yield leading to detection of only 2/42 additional cases with del(5q). In our cohort, the non-del(5q) patients with normal karyotype and those with trisomy 8 or microduplication on chromosome 8 were associated with a favorable response to LEN. Disclosures: Sekeres: Celgene: Consultancy, Honoraria, Research Funding. List:Celgene: Research Funding. Maciejewski:Celgene: Research Funding

Microbiomic profiles of bile in patients with benign and malignant pancreaticobiliary disease.

BackgroundThe prognostic and pathophysiologic significance of the biliary microbiota in pancreaticobiliary malignancies is little understood. Our goal was to find malignancy-related microbiomic fingerprints in bile samples taken from patients with benign and malignant pancreaticobiliary diseases.MethodsBile specimens were collected from consenting patients during routine endoscopic retrograde cholangiopancreatography. We used PowerViral RNA/DNA Isolation kit to extract DNA from bile specimens. The Illumina 16S Metagenomic Sequencing Library Preparation guide was used to amplify the bacterial 16S rRNA gene and create libraries. QIIME (Quantitative Insights Into Microbial Ecology), Bioconductor phyloseq, microbiomeSeq, and mixMC packages were used for post-sequencing analysis.ResultsOf 46 enrolled patients, 32 patients had pancreatic cancers, 6 had cholangiocarcinoma and 1 had gallbladder cancer. Rest of the patients had benign diseases including gallstones, and acute and chronic pancreatitis. We used multivariate approach in mixMC to classify Operational Taxonomic Units (OTUs). Doing this, we found a predominance of genera Dickeya (p = 0.00008), [Eubacterium] hallii group (p = 0.0004), Bacteroides (p = 0.0006), Faecalibacterium (p = 0.006), Escherichia-Shigella (p = 0.008), and Ruminococcus 1 (p = 0.008) in bile samples from pancreaticobiliary cancers as compared to benign diseases. Additionally, bile samples from patients with pancreatic cancer exhibited a predominance of genus Rothia (p = 0.008) as compared to those with cholangiocarcinoma, whereas bile samples from patients with cholangiocarcinoma exhibited a predominance of genera Akkermansia (p = 0.031) and Achromobacter (p = 0.031) as compared to those with pancreatic cancers.ConclusionsBoth benign and malignant pancreaticobiliary diseases have distinct microbiomic fingerprints. The relative abundance of OTUs in bile samples varies between patients with benign and malignant pancreaticobiliary diseases, as well as between cholangiocarcinoma and pancreatic cancer. Our data suggest that either these OTUs play a role in carcinogenesis or that benign disease-specific microenvironmental changes differ from cancer-specific microenvironmental changes, resulting to a clear separation of OTU clusters. We need more research to confirm and expand on our findings

Somatic Mutational Screen For Improved Prediction Of The Outcomes Of Epigenetic Therapy In MDS

Abstract Hypomethylating agents decitabine and azacitidine are standard treatments for MDS. In their use, one hopes to rectify cytopenias and prolong survival by retarding further disease progression. However, individual treatment responses vary from complete remissions (CR) to complete refractoriness. In general, at least months of therapy is needed prior to assessing response. Thus, patients may need to be subjected to prolonged exposure to ineffective therapy, suffering toxicities without clinical benefit, while alternative and potentially more effective treatments are delayed. Currently, there are no reliable phenotypic or mutational markers for predicting response to hypomethylating agents. Once whole exome sequencing (WES) became available for more routine analysis, we theorized that somatic mutational patterns may help identify patients who would most benefit from these drugs, thereby maximizing response rate by rational patient selection. To pursue this hypothesis, we screened a cohort of 168 patients with MDS who received either azacitidine or decitabine for the presence of somatic mutations. Only those who received sufficient therapy, i.e., completed at least 4 cycles, were selected for outcome analysis. WES and targeted deep NGS for a subset of 60 genes most frequently affected by somatic mutations in MDS (as determined in a set of 200 exome MDS project, see abstract from our group) was applied to 94 evaluable patients. Median age was 68 years (range, 26-85), 34% were female, and MDS subtypes were as follows: RA/RCUD/RARS 7%, RCMD 20%, RAEB-1/2 32%, MDS/MPN & CMML-1/2 21%, and sAML 16%. Response was assessed using IWG 2006 criteria at 4 and 7 months after therapy initiation. Overall response was 34%; rate of CR (including marrow/cytogenetic CR) was 22%, any HI 7%, SD 19%, and no response 35%. The cohort was then dichotomized into “responders” (N=64) and “non-responders” (N=69) with responders classified as those achieving CR/PR or any HI. Baseline patient characteristics were similar between both groups, including average age at treatment initiation, sex, disease subtypes, proportion of abnormal/complex karyotypes, and presence of common cytogenetic aberrations. Overall, the most frequently mutated genes include: TET2 (12%), IDH1/IDH2 (5%), SRSF2 (11%), ASXL1 (28%), SF3B1 (13%), RUNX1 (11%), EZH2/EED/SUZ12 (11%), SETBP1 (6%), CBL (7%), and PPFIA2 (10%). For some analyses we also divided mutations into functional gene families; e.g., DNMT family (DNMT1, DNMT3A, DNMT3B), PRC2 family (EZH2, EED, SUZ12, JARID2, RBBP4, PHF1), IDH family (IDH1, IDH2), CBL family (CBL, CBLB), RAS family (NRAS, KRAS, HRAS, NF1, NF2, RIT1, PTPN11), and among others. The most common molecular abnormalities in responders included the presence of complex karyotype (19% vs. 26% in refractory), del7q/-7 (18% vs. 22%), del5q (19% vs. 15%), and mutations in DNMT3 (25% vs. 22%), ASXL1 (25% vs. 32%), and others. Similarly, the most common defects found in refractory included also the U2AF1/2 family of genes (16% vs. 7% in responders). When compared and selected by the lowest p value, the top mutations in terms of predicting response were SRSF2 (OR 2.4), cohesin (5.1), ATM (OR 5.6) and PHF6 (OR 4.22). Mutations predicting non-response include RAS (OR .3), U2AF1/2 (OR 0.4) and LUC7L defects (OR .53). To generate better predictors, we have combined mutations in “either/or” fashion. For instance, the presence of either SRSF2 and cohesin (p=.0318) or cohesin and PHF6 mutations (p=.02) will be considered predictors of response and the presence of either or RAS/U2AF1(p=.019) and cohesin/ATM (p=.008) and SRSF2 (p=.006) predictors of refractoriness. In sum, mutational patterns may be helpful in identifying patients who may benefit from hypomethylating therapies. Identification of the most predictive genes could guide development of molecular marker-based selection of patients for hypomethylating agent therapy, but will require ongoing analysis and additional prospective testing for validation Disclosures: Makishima: AA & MDS international foundation: Research Funding; Scott Hamilton CARES grant: Research Funding. Maciejewski:NIH: Research Funding; Aplastic anemia&MDS International Foundation: Research Funding

Acquired Molecular Defects in Spliceosome Machinery: Novel Pathogenetic Pathways in Myeloid Leukemogenesis

Abstract Abstract 271 In MDS and other myeloid malignancies, deletions of chromosomal material can lead to decreased gene expression. Inactivating mutations may have similar consequences leading to decreased or absent gene function. Through these events dysfunction of tumor suppressor genes (TSGs) constitutes the key pathogenic mechanism in clonal evolution. In recent years, a large number of new somatic mutations affecting a variety of TSGs have been identified. In the search for new mutational events associated with MDS subtypes or phenotypes, we have applied whole exome sequencing to a large group of MDS patients. In a systematic analysis of somatic events screened for recurrence and potential functional significance, we noted several somatic mutations affecting genes involved in the splicing machinery. The somatic SF3B1 mutation, initially found in a patient with refractory anemia with ring sideroblasts (RARS) and thrombocytosis (T), was subsequently detected in 22/32 patients with RARS/RARST, but not in 58 patients with other forms of MDS and MDS/myeloproliferative neoplasms (MPN) and <15% ring sideroblasts. However, in another index case, we have identified a mutation in another member of the spliceosome gene family: U2 snRNP auxiliary factor (U2AF)1 (chromosome 21q22.3), encoding the splicing factor SR family protein which closely interacts with SF3B1 and plays a critical role in recognition of the pre-mRNA branch sites. Subsequent targeted screening detected additional mutations in a total of 23 of 247 adult patients with secondary and primary acute myeloid leukemia (AML) (9%), advanced forms of MDS (11%), and lower-risk MDS (6.5%). U2AF1 mutations were most frequently observed in chronic myelomonocytic leukemia (CMML) (17%) and unlike SF3B1 mutations (with which they were mutually exclusive) were found only in 2/36 RARS/RARSt patients (6%). Similar to SF3B1, no mutations were found in juvenile myelomonocytic leukemia (JMML) and pediatric AML (N=112). Based on the chromosomal location of U2AF1 we next examined trisomy 21 and UPD21q. Homozygous mutations were found in 1 case, and, 2 copies of the mutation were detected in trisomy 21. In addition, we identified a 7-Mbp deletion encompassing U2AF1, resulting in reduced copy number of wild type. In serial samples collected at initial presentation of MDS in patients who subsequently progressed to AML, U2AF1 was identified from the very beginning of the clonal process. In total, we have identified 4 different missense mutations, located in 3 residues (S34, R156 and Q157) in 2 zinc finger domains, the most common of which was predicted to affect amino acid S34 and Q157 (in 10 and 11 patients, respectively). U2AF1 and other spliceosome proteins are abundantly expressed in CD34 cells: analyses of MDS samples showed that expression of U2AF1 was decreased (<2 fold) in 7/55, 8/80 and 12/48 patients with RA, RA with excess blasts, and RARS. Finally, after adjustment for other confounding factor mutations in U2AF1, we determined that these lesions were associated with decreased overall survival (p=.08) in the CMML cohort. Of note is that mutations of DNMT3A and ASXL1 genes frequently coincide with U2AF1 mutations, which are often present in patients with normal cytogenetics. Discovery of other mutations in spliceosomal genes LUC7L2 (7q34) and PRPF8 (17p13.3) in a similar phenotype further substantiated the notion that spliceosomal machinery TSGs are frequently targeted by mutations. LUC7L2 is associated with the U1 snRNP spliceosomal subunit and involved in recognition of splice donor site. PRPF8 is a component of the U5/U4/U6 tri-snRNP and participates in both U2 and U12 splicing. Interestingly, loss of heterozygosity of these 2 spliceosome associated gene regions were also seen in cases with U2AF1 mutations. Moreover, a LUC7L2 nonsense mutation was detected in a secondary AML with U2AF1 mutation. For the further evaluation of functional significance of U2AF1 mutations, splice status was examined by RT-PCR based analysis. In mutant cases, pre-mRNA of several genes, including P53 and PRPF8 were not completely spliced and normally spliced fragments were decreased compared with wild type cases or healthy donors. Unspliced P53 genes were wild type. Our findings suggest that different components of spliceosome dysregulation might have a synergetic effect on clonal evolution in myeloid malignancies, and that dysfunction of RNA splicing is a common pathway in leukemogenesis. Disclosures: No relevant conflicts of interest to declare

Clinical and Molecular Features Of Young Patients With Myelodisplastic Syndromes (MDS)

Abstract MDS typically affects older adults, and hereditary factors have been considered less contributory to disease pathogenesis. Moreover, their impact is obscured by the complexity of the clinical presentation and history. Similarly, familial MDS and pediatric MDS is rare and likely distinct from adult MDS occurring in younger adults. Younger MDS patients (pts), excluding those who present with treatment-related disease, may represent a distinct subtype of MDS characterized by a specific molecular pattern of lesions. We compared two groups of MDS pts focusing on pathological diagnosis at presentation, family history of solid malignancies and blood disorders (Leukemia and MDS) in first and second degree relatives, cytogenetic abnormalities and somatic mutations. Our analysis of 1030 MDS pts included MDS, MDS/myeloproliferative neoplasm (MPN) and secondary acute myeloid leukemia (sAML) pts. Overall the median age at presentation of this population was 71years (range 14-100); we classified the younger subset as those falling into the lower 8thpercentile of age to identify. Accordingly, the younger population was characterized by age less than 50 years (range 14-49; median age 41), and the older population age ≥ 50years (range 50-100; median age 75). Treatment-related MDS was excluded. Younger MDS pts more frequently presented with higher-risk disease compared to the older population (46% vs. 31%; P=.004). There was no significant difference between the two groups with regard to family history of cancers (40 vs. 47%; P=.21) and blood disorders (10 vs. 6%; P= .1). When we compared cytogenetic abnormalities between these patient subsets, there was no difference in detection of rate of abnormal cytogenetics (53% vs. 52%; P=.5) or complex karyotype (23 vs. 25%; P=.86). However, del 20q was more common in the older subset (19 vs. 6%; P=.03). We then investigated somatic mutational patterns using new generation deep sequencing for the 60 most commonly encountered MDS mutations (defined in the 200 MDS exome cohort presented in other abstract from our group). Data were available for 26 younger pts and 179 older pts. By analyzing comprehensive mutational spectrum, the average number of somatic mutational events (mean; 2.4/case) was significantly higher in the older subgroup compared to the younger (1.8/case; P<.001). RUNX1, PHF6, TP53 (12% each) are the most frequently affected genes in MDS associated with the younger population. Interestingly, germline mutations of these 3 genes are all associated with congenital syndromes, which lead to susceptibility for hematological neoplasms. Conversely, somatic mutations of TET2 (24%) and ASXL1 (15%) were most prevalent in the older MDS cohort. Notably, these 2 genes associated with older populations were less prevalent in younger MDS cases (<4%; P=.02 and < 4% P=.11 for TET2 and ASLX1 respectively). In contrast, there was no significant difference between these subgroups (old vs. young MDS) in the frequency of RUNX1 (9 vs. 12%; P=.67), U2AF1 (11 vs. 12%; P=.88), BCOR family (9 vs. 15%; P=.35), PRC2 family (10 vs. 4%; P= .34), RAS family (11 vs. 12%; P=.88), or many other gene mutations. In sum, 8% of MDS pts present at a younger age in our cohort. MDS in younger pts presents with more advanced disease and is less commonly affected by del20q- and TET2 mutations, consistent with less common myeloproliferative features in this population. Disclosures: Makishima: AA & MDS international foundation: Research Funding; Scott Hamilton CARES grant: Research Funding