ALBERT

Description: Bone marrow (BM) fibrosis is a key pathomorphologic feature of patients (pts) with primary myelofibrosis (PMF) and the fibrotic phases of essential thrombocythemia (post-ET MF) and polycythemia vera (post-PV MF). The degree of BM fibrosis appears to correlate with survival. Indeed worse survival has been associated with increased BM fibrosis. The BM stromal microenvironment is important in the pathogenesis of BM fibrosis. Cellular components (fibroblasts, macrophages, endothelial cells, adipocytes), structural fibrils (collagen, reticulin) and extracellular matrix components are all forming elements of the BM stroma. Increased stromal fibrosis has been linked to abnormalities in the number/ function of megakaryocytes and platelets in hematologic diseases. Several cytokines like Platelet Derived Growth Factor (PDGF) and Transforming Growth Factor-Beta (TGF-b) have been also linked to the pathophysiology of BM fibrosis. PDGF has been shown to increase fibroblast growth in megakaryocytes and platelets although increased PDGF did not correlate with increased production of either reticulin or collagenous fibrosis. Moreover, PMF pts have increased TGF-b levels in platelets, megakaryocytes, and monocytes. Nitric Oxide (NO) is a ubiquitous gas important in physiologic processes particularly vasodilatation. Dysregulation of NO levels has been implicated in pulmonary hypertension (PH), hemoglobinopathies, and cardiovascular diseases. In Peyronie’s disease, a localized fibrosis of the penile tunica albuginea, increased NO production by expression of iNOS decreases collagen deposition by neutralization of profibrotic reactive oxygen species and decreased myofibroblast formation. Aside from its role in maintaining normal vascular tone, NO also plays a role in fibroblast formation and collagen biosynthesis. We previously reported that ruxolitinib, a JAK1/2 inhibitor restores NO levels leading to improvement of PH in MF pts (Tabarroki et al., Leukemia 2014). We now hypothesize that plasma/serum NO level is a key regulator of BM fibrosis in MF and that ruxolitinib treatment (Tx) leads to improvement of BM fibrosis by NO modulation. Using a Sievers 280i NO analyzer we measured the plasma/serum NO level of a large cohort (n=75) of pts with myeloid and myeloproliferative neoplasms (MPN) [MDS, RARS/RCMD=8; MPN, ET=8, PV=8, MF=24, Mastocytosis=7; MDS/MPN, CMML=11, MDS/MPN-U, RARS-T=9]. Healthy subjects (n=10) were used as a control. MPN pts had low NO (nM) levels among the pts studied with the lowest level found in MF pts: MF=30.31±11.8, PV=39.0±16.1, ET=36±20.3, RARS=74.6±41.7 (P=.01), CMML=84.4±89.2 (P=.04), RCMD=163.4±103.8 (P

Description: SF3B1 mutations disrupt normal pre-mRNA splicing to cause disease. Drugs inhibiting the interaction between the SF3b complex and RNA or agents degrading auxiliary splicing factors are being tested as new avenues for targeted therapy in myeloid neoplasia (MN) with SF3B1 mutations. Here we describe the ability of small molecules to restore altered RNA processes in SF3B1MT MN. We previously reported (Visconte, ASH 2018) the identification of the small molecule 4-pyridyl-2-anilinothiazole (PAT) which showed growth inhibition of CRISPR/Cas9 SF3B1+/K700E cells and primary SF3B1MT cells. PAT did not influence the growth of other cell models without (THP1, MOLM13FLT3, OCIAML3DNMT3A, SIGM5TET2/DNMT3A, K562PHF6) and with other splicing factor mutations (K562U2AF1, K562LUC7L2). We now describe data from medicinal chemistry, transcriptome, and in vivo studies to advance drug development for SF3B1MT MN. SAR studies focused on logical and systematic modifications of PAT, e.g., i) replacement of the 2,4-disubstituted thiazole spacer ring with other heteroatom containing rings (5,6,7 membered aromatic or aliphatic ring structures); ii) alternative linking groups for the NH linker of the aniline of the tail region (sulfonamide, amide, substituted amine linkers); iii) alternative substituted aromatic and aliphatic ring structures for the phenyl head region substituent, led us to identify permissive sites for further chemical optimization. For example, a 4-chlorophenyl analog demonstrated activity [IC50, 3μM] similar to PAT. Competitive repopulation assays of bone marrow (BM) cells from dual reporters (ACTBtdTomato; EGFP) B6.GtROSA26 mixed with BM cells from conditional knock-in Sf3b1+/K700E mice injected in pre-lethally irradiated B6.SJL-PtprcaPepcb/BoyJ (CD45.1) recipients (n=18) were used as a preclinical murine model. This model then allowed i) demonstration of drug efficacy in reducing the competitiveness of SF3B1MT cells and ii) evaluation of therapeutic index in normal hematopoiesis. Post-transplant recovery, recipients of B6.GtROSA26 cells underwent PAT treatment (10 mg/Kg/IP/5 days weekly) for a period of 6 weeks without showing any signs of distress or drug intolerance (drop in blood count, weight loss, abdominal swelling, liver or kidney toxicity). Two weeks after transplantation, donor Sf3b1+/K700E cells had an engraftment capability similar to that of donor B6.GtROSA26 cells (83.6 ± 4 vs. 86.4 ± 2.4) when transplanted as a sole graft in CD45.1 recipients. PAT reduced almost half the percentage of Sf3b1+/K700E donor cells at 6 weeks of treatment (47.4%) vs. pre-treatment (83.6%). In mixed (1:1) BM transplants, Sf3b1+/K700E cellshad a repopulative disadvantage against competitors B6.GtROSA26 contributing for 16% of the marrow reconstitution. Similar to single graft transplants, PAT decreased the percentage of Sf3b1+/K700E cells at 6 weeks vs. pre-treatment (average, 6% vs. 16%) in chimeras. Consistent with the lack of toxicity of PAT treatment B6.GtROSA26 cells in chimeras were not affected by PAT and gradually repopulated the host (post-treatment, 80% vs. pre-treatment, 64%). Subsequently, we focused our efforts identifying important genes known to be dysregulated in MDS that were mostly influenced by drug treatment and minimally affected in normal cells. Our approach was based on the analyses of genes linked to erythropoiesis (a key hallmark of low-risk MDS). In normal hematopoiesis TGF-β signaling inhibits terminal erythroid maturation. Out of 13,775 genes, 5% (664/13,775) were found differentially expressed between CRISPR/Cas9 SF3B1+/K700E and parental cells of which 60% of these genes were significantly up-regulated and 40% down-regulated. Pathway analysis showed that the expression levels of SMAD family of genes and GDF factors changed significantly upon drug treatment. SMAD7 mRNA levels are 3-fold lower in MDS CD34+ cells (n=159) compared to the ones of healthy subjects (n=17) (GEO accession GSE58831) leading to TGF-β over activation. PAT treatment normalized SMAD7 expression levels in CRISPR/Cas9 SF3B1+/K700E cells by 3-fold while reducing the levels of GDF11. In summary, we have identified new drug entities that are modulators of transcriptomic changes which decrease the competitiveness of SF3B1MT cells. These results suggest combination therapies with current TGF-β pathway inhibitors. Disclosures Advani: Glycomimetics: Consultancy, Research Funding; Kite Pharmaceuticals: Consultancy; Amgen: Research Funding; Pfizer: Honoraria, Research Funding; Macrogenics: Research Funding; Abbvie: Research Funding. Kelly:Novartis, Bayer, Janssen, Pharmacyclics, Celgene, Astrazeneca, Seattle Genetics: Honoraria, Speakers Bureau; Takeda: Research Funding; Genentech, Verastem: Consultancy. Sekeres:Syros: Membership on an entity's Board of Directors or advisory committees; Millenium: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees. Maciejewski:Novartis: Consultancy; Alexion: Consultancy.

Description: Isochromosome 17q [i(17q)], a poor prognostic cytogenetic abnormality is a product of the breakage or inappropriate division of the pericentromere leading to the duplication of the long and loss of the short arm of chromosome 17. The region of the breakpoints maps at 17p11, a region encompassing a key tumor suppressor gene: TP53. I(17q) are detected in myelodysplastic/ myeloproliferative neoplasms (MDS/ MPN), chronic myeloid leukemia (CML), and acute myeloid leukemia (AML). This abnormality can occur as a sole structural abnormality or in combination with other chromosomal defects. The presence of i(17q) is associated with poor therapeutic response, disease progression, and an unfavorable clinical outcome. Elucidation of the molecular architecture of patients (pts) carrying i(17q) may lead to better understanding of disease biology and development of novel compounds that can target this disease. We selected 11 pts with i(17q) to characterize their genomic differences. We applied whole exome sequencing (WES) in order to define latent molecular defects explaining the clinical phenotype of this disease. The index case was a male MDS/MPN pt with isolated i(17q), 27% RS, hypercellular bone marrow (BM), mild splenomegaly, and atypical megakaryocytes. The pt developed 7% BM blasts without clinical response to growth factors. Molecularly this pt was a wild type SF3B1, a gene frequently mutated in RARS-T and associated with lower transformation rate to leukemia, better survival, and good/intermediate risk cytogenetic abnormalities. WES was performed on 2 ug of total DNA extracted from BM cells. Non-clonal CD3+ cells were used as source of germ-line control. Twenty-millions reads were run on an Illumina HiSeq2000 sequencer. Using a stringent bio-informatic algorithm developed in house, all variants were filtered based on a variation score (〉=30) and a coverage (30X) and the tumor nucleotide variation analysis was performed for each pair (tumor vs. germ-line), where only the variants unique to the tumor were retained. Variants were ultimately filtered in order to exclude SNPs by an in-house annotation and importing the hg19 SNP135. We detected 65 unique candidate genes. Four genes were confirmed to be somatic: 3 were novel: ZFP42 (4q35.2), P4HTM (3p21.31), and VPRBP (3p21.2) and 1 includes the newly discovered SETBP1 (18q12.3) gene. Three variants detected on the chromosome 17 had a wild type configuration. The subsequently genotyped all the pts (MDS/MPN/-U 3; AML 4; RCMD 1; CML 1; RAEB-1 2; mean age: 68 years; male/female: 8/3; i(17q)/other abnormalities:3/8) for the above genes and for a panel of genes known to be mutated in MDS/MPN and other diseases in order to find any genetic association explaining the disase phenotype. We applied Sanger sequencing to DNA derived from BM/peripheral blood cells (BM/PB:7/4) for the following genes and respective exons: TP53 (all exons), SF3B1 (13-16), SRSF2 (1-2), U2AF1 (2 and 6), TET2 (all exons), DNMT3A (18-23), IDH1/2 (4), CBL (8-9), N/KRAS (1-2), ASXL1 (12), JAK2 (12 and 14), EZH2 (16, 18 and 19), MPL (exon 10), BCAS3 (12, 15 and 16), FLT3 (11 and 17), and CSF3R (13,14, and 17). In total, we found 16 heterozygous missense mutations and 1 tandem duplication. We found somatic mutations in ZFP42, P4HTM, and VPRBP in 1 pt. The index case reported a mutation in SETBP1 and SRSF2. SF3B1 was detected as a sole abnormality in 1 patient. Of note, the patient with SF3B1 mutation (K700E) had 50% RS and achieved a complete hematologic remission after decitabine therapy. The most frequent mutations were found in SETBP1 and SRSF2. SETBP1 was found to be mutated in 4/11 (36.3%) pts (D868N, I871T, and G870S was common in 2 pts) while SRSF2 mutations (P95H/R) were found in 3/11 (27.2%) pts. Three pts showed concomitant SRSF2 and SETBP1 mutations. NRAS (G12D) was mutated in 1 pt and associated with SRSF2 and SETBP1 mutations. One pt showed mutations in TET2, JAK2, and TP53. Of note, this pt did not respond to treatment. One pt with MDS/MPN showed a mutation in CSF3R (Q741X), a novel gene discovered in chronic neutrophilic leukemia and atypical CML. The pt also has monosomy 7 and i(17q) abnormality. FLT3-ITD was found in 1 pt. As of last follow-up, only 2 pts remain alive. In sum, we found that poor risk molecular mutations in SRSF2 and SETBP1 are frequently found in i(17q) myeloid malignancies and may be the drivers of poor outcomes in this disease. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 2173 Poster Board II-150 Loss of heterozygosity (LOH) due to acquired uniparental disomy (UPD) is a commonly observed chromosomal lesion in myeloproliferative neoplasms (MPN) and myelodysplastic/myeloproliferative neoplasms (MDS/MPN) including chronic myelomonocytic leukemia (CMML). Most recurrent areas of LOH point towards genes harboring mutations. For example, UPD11q23.3 and UPD4q24 were found to be associated with c-Cbl and TET2 mutations, respectively. Cbl family mutations (c-Cbl and Cbl-b) have been associated with atypical MDS/MPN including CMML and juvenile myelomonocytic leukemia (JMML) as well as more advanced forms of MDS and secondary AML (sAML). Ring finger mutants of Cbl abrogate ubiquitination and thereby tumor suppressor function related to inactivation of phosphorylated receptor tyrosine kinases, Src and other phosphoproteins. TET2 mutations are present in a similar disease spectrum. The TET family of proteins is involved in conversion of methylcytosine to methylhydroxycytosine which cannot be recognized by DNMT1. Thereby, the proteins seem to counteract maintenance hypermethylation. In our screen of MDS/MPN, we found c-Cbl and Cbl-b ring finger mutations in 5/58 (9%) of CMML and AML derived from CMML, 2/39 (5%) MDS/MPNu, 4/21 (19%) JMML and 14/148 (9%) RAEB/sAML. In the same cohort, TET2 mutations were present in 37% and 14% of patients with MDS/MPN and MDS, respectively. Of note we did not find any TET2 mutations in JMML. We and others have also noted that TET2 and c-Cbl mutations were also detected in atypical chronic myeloid leukemia. While translocations resulting in BCR/ABL fusion characterize CML, we stipulated that in analogy to other chronic myeloproliferative diseases, TET2 and c-Cbl mutations may be also present in CML and contribute to phenotypic heterogeneity within BCR/ABL associated disorders. In particular, progression of CML to accelerated phase (AP) or blast crisis (BC) could be associated with acquisition of additional lesions. When 22 patients with CML chronic phase (CP) were screened, no TET2 and c-Cbl mutations were found. However, we identified 1 c-Cbl, 2 Cbl-b (6%) and 6 TET2 (12%) mutations in 51 patients with CML-AP (N=18) and CML-BC (N=33) with myeloid and lymphoid/mix 24 and 9 phenotype, respectively. These mutations were mutually exclusive. We also noted that TET2 mutations were present in 1/9 CML in BC with lymphoid phenotype. We subsequently screened Ph+ ALL cases (N=9) and found a TET2 mutation in 1 case but no Cbl family mutations. In contrast when 9 Ph- ALL cases were screened as controls, neither TET2 or Cbl mutations were found. SNP-A analysis revealed 2 cases of LOH involving chromosome 4 (UPD4q24 and del4) in a patient with lymphoid blast crisis and Ph+ ALL, respectively. However, UPD was not found in Cbl family gene regions (11q23.3 or 3q13.11). A homozygous deletion of Cbl-b region was seen in a CP patient. Cbl family mutations were associated with a more complex karyotype than TET2 mutations (67% vs. 17% cases with abnormal phenotype). Patients with Cbl family mutations were resistant to imatinib which was effective in only 2 out of 6 patients with TET2mutations. Dasatinib was effective in 2 patients with TET2 mutation. Median over all survival of progressed CML was 47, 49 and 48 months in patients with Cbl, TET2 or no mutations, respectively. In conclusion, our results indicate that Cbl family mutations can occur as secondary lesions in myeloid type aggressive CML (AP and myeloid BC), but not in lymphoid types. TET2 mutations were identified in both lymphoid BC and Ph1+ALL, as well as myeloid BC and AP. In contrast to CMML or JMML in which a vast majority of mutations are homozygous, all Cbl family mutations were heterozygous (no LOH). Similarly, all but two TET2 mutations were heterozygous (1 hemizygous in del4 and 1 homozygous case in UPD4q), suggesting that additional cooperating lesions affecting corresponding pathways may be present. These mutations likely represent secondary lesions which contribute to more either progression (CML) or more aggressive features (Ph+ ALL) and characterize disease refractory to therapy with imatinib. Disclosures: No relevant conflicts of interest to declare.

Description: Pharmacologic therapies that target the JAK-STAT pathway are clinically used to alleviate splenomegaly and disease-related constitutional symptoms in MF. However, it is clear that some patients develop intolerance or resistant to this therapy. Furthermore, there are MF related complications especially cytopenias that are not alleviated by these therapies. Therefore, alternative and complementarytherapies are warranted in the management of MF. We hypothesized that other pathways downstream of the JAK-STAT signaling pathway can play a role in the pathophysiology of MF. We used whole exome (WES) and RNA sequencing technologies to interrogate new molecular markers and pathways which can serve as novel targets for this disease. In 4 MF patients [JAK2 mutant (MUT) =2, and wild type (WT) =2], WES was performed using the Illumina platform. All of the variants were filtered based on PHRED score (〉=30) with coverage was set at 30X. Analysis of data in JAK2/MPL WT patients demonstrated the presence of 263 candidate genes. After clarifying the status of tumor nucleotide variants in each gene compared to germline (CD3+) fraction, 7 genes (RBL1, ADSS, ZNF717,MUC4, TUBB4Q and CDC25A) were selected for further somatic confirmation by direct sequencing. Among these genes, only alteration in CDC25A, a regulator of cyclinE/cdk2 (cyclin-dependent kinase-2) and cyclinA/cdk2 kinase, was confirmed to be somatic. This genetic change was previously reported as somatic by WES in lung cancer although not confirmed by direct sequencing (Bartkova et al, Nature, 2005, Apr 14; 434 (7035):864-70). Based on these observations and since CDC25A acts as a downstream effector of JAK-STAT signaling, we hypothesized that, CDC25A phosphatase, may be a driver in MF pathogenesis. The transcriptome of two patients, one MUT and one WT for JAK2 was then analyzed. RNA was isolated from bone marrow (BM) cells of healthy individuals (HI) (N=3). cDNA was made from 1.5-3 ug of RNA and fragmented for library preparation. RNA-sequencing was performed on 20 million sequence reads. Paired-end 90 base pair reads were generated on an Illumina HiSeq2000 sequencer and aligned to the human genome 19. RNA-splicing patterns were analyzed by a bioinformatics algorithm and gene expression analysis was carried out using GSEA (Visconte V; Blood. 2012). By using FDR80%) while JAK2 MUT samples had only a few positive megakaryocytes (

Description: Introduction: The effect(s) of co-morbid medical conditions on platelet function is poorly understood. In this retrospective EMR-based study, we analyzed the influence of various diseases on in vitro measures of platelet function - platelet function analyzer-100 (PFA-100) closure times, platelet aggregation (using light transmission aggregometry (LTA)), platelet dense granule release (using lumi-aggregometry), and platelet flow-cytometry for surface glycoproteins. We also examined their influence on VWF testing. Methods: Four hundred ninety seven patients who had platelet aggregation testing performed using LTA between August 2008 and August 2013 were included in our study. Co-morbidities at the time of testing were recorded. Propensity score matching for each individual disease was used to adjust for relevant covariates. We used a 1:1 nearest neighbor match without replacement, with caliper width set to 0.2 times the standard deviation of the logit of the propensity score. Following matching, Fisher's exact test or Chi square test was used as appropriate to assess the association between categorical variables, while the Mann-Whitney test was used to test the association between categorical and continuous measures. Pearson co-efficient was used to assess the correlation between continuous variables. P 〈 0.05 was considered significant. Results: 1) Congestive heart failure (n = 44) was associated with impaired platelet aggregation in the presence of arachidonic acid (p = 0.001) and collagen (p = 0.009), as well as impaired dense granule release in the presence of collagen (p = 0.002) and epinephrine (0.012). It was also associated with abnormal aggregation (p = 0.024) and release (p = 0.028) in the presence of ≥ 2 agonists in the respective panels. Diastolic heart failure (n = 25) was found to be associated with impaired aggregation in the presence of ADP (p = 0.007), collagen (p = 0.001), or arachidonic acid (p = 0.007), and to ≥ 2 agonists in the aggregation panel (p = 0.008). Systolic heart failure (n = 26) was not associated with abnormalities in aggregation or release. 2) Severe aortic stenosis (n = 17) was associated with prolonged collagen/ADP (p = 0.003) and collagen/epinephrine (p

Description: Abstract 312 Prognosis in myelodysplastic syndromes (MDS) is heavily influenced by cytogenetics. Trisomy 8 (+8) is reported in 15–20% of MDS patients (pts) and is one of the most commonly identified karyotypes in this disease. Sole +8 is an intermediate-risk karyotype in MDS by the International Prognostic Scoring System (IPSS). However, pts with +8 myeloid malignancies exhibit wide clinical heterogeneity. In chronic myelomonocytic leukemia (CMML), +8 is considered high-risk, while in MDS functional data suggests an “immunopathologic” cause that is responsive to immunosuppressive agents and confers a good prognosis. Single nucleotide polymorphism array (SNP-A) and molecular technologies (next generation sequencing) have led to further refinement of prognosis in MDS, and subsequent discovery of molecular mutations with distinct effects on outcomes. We hypothesized that the differential outcomes noted in +8 MDS are primarily influenced by both clinicomorphologic features and the acquisition of new cytogenetic (isolated, +1, ≥2) and molecular defects. To further characterize the clinical and molecular behavior of +8 myeloid neoplasms, we analyzed 68 pts seen at the Cleveland Clinic with a +8 clone. Hematologic, bone marrow (BM), cytogenetic (metaphase cytogenetic [MC]/SNP-A) and survival data were collected. Survival comparisons were made by Kaplan-Meier analyses. Cox-proportional hazard ratio was used to determine factors predictive of outcomes. Response was evaluated per International Working Group 2006 criteria. Most (69%) pts were male; median age 69 years (38–89), and median follow-up 15 months. 69% (47/68) had MDS, 10% (7/68) MDS/MPN, 3% (2/68) MPN and 18% (12/68) AML. 41% of pts had an isolated +8 abnormality (+8 (i)), 16% had one additional abnormality (+8plus1), and 43% had ≥2 additional abnormalities defined as +8complex. By IPSS, Int-1=34%, Int-2=25%, high=42%. SNP-A data were available in 51% of the cases and detected new lesions in 60% of them (gains[46%], losses[43%], UPD[23%]). Clinically, pts with +8complex had higher median peripheral blood blasts (PB) compared to +8plus1 and +8(i) (3.5 vs 0 vs 0%,p=.04). By treatment, pts received high intensity (BMT±high dose chemo=35%), low intensity (hypomethylating agents [HMA]± lenalidomide=37%) or supportive therapies=28%). Overall response rate was 47%, with 14% CR. By cytogenetic grouping, +8complex had lower response rates compared to +8 with additional karyotype (30 vs 60 vs 52%; p=.06). Median overall survival (OS) was 15 months, and median event free survival (EFS) was 8 months, with worse OS noted in +8 complex compared to +8 plus1 and +8(i) (OS=11 vs 22 vs 29 months, p=.02; EFS=5 vs 10 vs 12 months; p=.04). To investigate the biologic rationale of these observations, we performing direct sequencing for poor prognostic genes in myeloid malignancies, such as ASXL1, IDH1/2, EZH2, K/NRAS, CBL and TP53 and for predictors of good outcomes/response like SF3B1/TET2. Molecular mutations were identified in 9/24 (38%) pts, with mutational frequencies within +8(i) (12 pts) of TET2 (42%), ASXL1 (42%), K-/NRAS (17%), SF3B1 (17%), and TP53 (0%). None of these mutations were detected in the +8plus1 or +8complex cohorts except for TP53 in one +8complex pt. No IDH1/2/EZH2/CBL mutations were found in the entire +8 cohort. Interestingly, mutations in TET2 conferred a better OS (88 vs 12 mos; p=.01). In +8 myeloid malignancies, ASXL1 mutations did not impact OS. We are currently performing whole exome sequencing and other immunogenetic studies in +8 pts to help identify factors that contribute to these group outcomes. To further define factors predictive of worse outcomes in +8 pts, univariate and multivariate analyses were performed and a predictive model of OS was designed. Using a simple scoring system, one point each was assigned to LDH ≥240, platelets 5%, and 2 points to an ANC 2], median OS=4.6 months; p

Description: Introduction: With the expanding repertoire of antiplatelet drug targets and therapies, quantifiable parameters to assess their efficacy can prove to be useful in clinical decision-making. In this retrospective analysis we examined patients who had platelet aggregation testing done at our center between August 2008 and August 2013, focusing on those who were on some form of antiplatelet therapy during testing. Our goal was to define the impact of platelet aggregation testing on decision-making regarding continuation or change in antiplatelet therapy. Methods: Light transmission aggregometry (LTA) was used to assess efficacy of treatment with antiplatelet agents. Inhibition of platelet aggregation in response to ADP and arachidonic acid are reflective of the therapeutic effect of aspirin, while inhibition of platelet aggregation in response to ADP reflects the effect of P2Y12 receptor antagonists. As per parameters developed at our center, the combination of arachidonic acid aggregation

Description: Introduction: Commonly used platelet function tests include Platelet Function Analyzer -100 Closure Time (PFA-100), used as a screening test, and platelet aggregation testing by Light Transmission Aggregometry (LTA), which can help differentiate between various types of platelet function defects and guide further testing. In this study, we assessed the indications for platelet aggregation testing at our center, and the effect of factors that may interfere with the outcomes of testing. Methods: This was a retrospective electronic medical records based study in which we included all patients in our healthcare network who had platelet aggregation testing done using LTA between August 2008 and August 2013. Routine descriptive measures were used for frequencies and proportions. McNemar test was used for comparison of paired nominal variables and Wilcoxon signed-rank test was used for comparison of paired continuous variables. P value 〈 0.05 was considered significant. Results: Four hundred ninety seven patients had platelet aggregation testing performed during the 5-yr study period. Among these, 315 (63%) patients had antecedent screening with PFA-100 with 157 (31%) showing at least one abnormality. Two hundred forty nine (50%) patients underwent some form of further testing after LTA, including VWF analysis (42%), platelet flow cytometry (19%) and/or electron microscopy (1%). Two hundred fifty six (51%) patients had at least one factor previously known or suspected to interfere with platelet aggregation testing (platelet count