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Clonal hematopoiesis is common in older persons and is associated with an increased risk of hematologic cancer. Here, we review studies establishing an association between clonal hematopoiesis and hematopoietic malignancy, discuss features of clonal hematopoiesis that are predictive of leukemic progression, and explore the role of hematopoietic stressors in the evolution of clonal hematopoiesis to acute myeloid leukemia or myelodysplastic syndrome. Clonal hematopoiesis due to point mutations or structural variants, such as copy number alterations, are associated with an approximately 10-fold increased risk of hematopoietic malignancy. Although the absolute risk of hematopoietic malignancy is low, certain features of clonal hematopoiesis may confer a higher risk of transformation, including the presence of TP53 or splicesome gene mutations, a variant allele fraction greater than 10%, the presence of multiple mutations, and altered red blood indices. Clonal hematopoiesis in the setting of peripheral blood cytopenias carries a very high risk of progression to a myeloid malignancy and merits close observation. There is emerging evidence to suggest the hematopoietic stressors contribute both to the development of clonal hematopoiesis and progression to hematopoietic malignancy. Specifically, there is evidence that genotoxic stress from chemotherapy or radiation therapy, ribosome biogenesis stress, and possibly inflammation may increase the risk of transformation from clonal hematopoiesis to a myeloid malignancy. Models that incorporate features of clonal hematopoiesis along with an assessment of hematopoietic stressors may eventually help predict and prevent the development of hematopoietic malignancies.

Diagnosis of low-grade myelodysplastic syndromes (LG-MDS) is one of the most challenging in hematopathology as it relies predominantly on morphologic assessment of dysplasia. Prior studies have demonstrated poor interobserver agreement among pathologists. Histomorphological evaluation of bone marrow core biopsy samples remains the gold standard for diagnostic workup of LG-MDS, including myelodysplastic syndromes (MDS) and other myeloid neoplasms. However, this approach may be subjective, and cannot quantitatively assess subtle differences in marrow topography and the cellular microenvironment. Multiparametric in situ imaging (MISI) through various techniques enables multiple biomarker detection in a single tissue. BostonGene has developed an AI-based image analysis platform to reveal spatial information and subtle histomorphologic features in an objective, quantitative fashion. Here, we demonstrate the potential for automated AI-based imaging analysis of MISI to assist in the differentiation of LG-MDS samples from normal marrow tissues (NBM). Decalcified human bone marrow core biopsy tissues from LG-MDS (n=6) and uninvolved staging marrows (NBM, n=4) were first prepared by immunofluorescence-based MISI via staining with DAPI and CD34, CD38, CD117, CD71, CD15, and CD61 antibodies. BostonGene analyzed the resulting images (fig.1) using a proprietary AI-based imaging platform to identify cells by segmentation performed with the pre-trained instance segmentation neural network. Cell types were identified with mean marker expression values using an accelerated version of BostonGene's phenograph clustering algorithm. Pathologists manually masked fat and bone trabeculae. Using a combination of cell size/shape parameters and antigen expression levels, the following unique cell types were identified: myeloblasts, proerythroblasts, erythroid normoblasts, maturing granulocytes, megakaryocytes, mast cells, plasma cells, and B-cell precursors (hematogones). Data revealed differences in the cellular content of NBM and LG-MDS samples, and separation of LG-MDS samples with the del(5q) subtype (n=2). While linear slender islet-like small clusters of erythroid normoblasts were detected in NBM, we observed a chaotic arrangement of them in LG-MDS samples. In LG-MDS samples, we found an increase in the total number of erythroid normoblasts from 17% to 31%, LG-MDS-del(5q) had 14%. The ratio of maturing granulocytes to erythroid normoblasts (M:E ratio) was significantly lower in LG-MDS (0.63) than in NBM (1.95). The M:E ratio generated by MISI strongly correlated to the M:E ratio produced by manual differential count of bone marrow aspirate samples (R=0.83, p < 0.003). Additionally, fewer hematogones were identified in LG-MDS marrows compared to NBM samples, as reported by others using orthogonal methods. Topographic analysis showed the fat to cellular tissue area ratio was higher in NBM (0.73) than LG-MDS (0.41), but the ratio of trabecular area to total tissue area was higher in LG-MDS (1.67) than NMB (0.74). Spatially, myeloblasts and megakaryocytes were found closer to trabeculae in NBM than LG-MDS;12 different cell communities were identified;2 of them (cluster 3 - erythroid normoblasts enriched, cluster 5 - erythroid normoblasts contacting proerythroblasts) were distributed statistically significantly differently in NBM and LG-MDS samples, indicating the use of MISI with AI-based imaging to distinguish LG-MDS from NBM. Patients of MDS-del(5q) subtype differ significantly from other MDS samples and are more similar to NBM. AI-based image analysis applied to MISI of bone marrow tissue revealed multiple cell types in single tissue sections, along with histologically subtle differences in topography between NBM and LG-MDS samples. These results highlight the importance of integrating in situ tissue analysis with techniques that examine single cell characteristics for a more comprehensive picture of the differences between normal tissue and tumor samples. Coupling sophisticated imaging analytics with this imaging method may provide a more powerful tool for novel biomarker discovery of prognostic and therapeutic significance in the management of MDS and other marrow-based disorders. Figure 1 Figure 1. Disclosures Svekolkin: BostonGene Corp.: Current Employment, Current holder of stock options in a privately-held company, Patents & Royalties. Varlamova: BostonGene Corp.: Current Employment, Current holder of stock options in a privately-held company, Patents & Royalties. Galkin: BostonGene Corp.: Current Employment, Current holder of stock options in a privately-held company, Patents & Royalties. Akaeva: BostonGene Corp.: Current Employment, Current holder of stock options in a privately-held company, Patents & Royalties. Smirnova: BostonGene Corp.: Current Employment, Current holder of stock options in a privately-held company, Patents & Royalties. Ovcharov: BostonGene Corp.: Current Employment, Current holder of stock options in a privately-held company, Patents & Royalties. Polyakova: BostonGene Corp.: Current Employment, Current holder of stock options in a privately-held company, Patents & Royalties. Tabakov: BostonGene Corp.: Current Employment, Current holder of stock options in a privately-held company. Postovalova: BostonGene Corp.: Current Employment, Current holder of stock options in a privately-held company, Patents & Royalties: BostonGene. Koltakova: BostonGene Corp.: Current Employment, Current holder of stock options in a privately-held company. Gunn: BostonGene Corp.: Current Employment, Current holder of stock options in a privately-held company. Bagaev: BostonGene Corp.: Current Employment, Current holder of stock options in a privately-held company, Patents & Royalties: BostonGene.

Severe congenital neutropenia (SCN) is characterized by persistent neutropenia and risk of invasive, life-threatening infection as well as transformation to hematopoietic malignancy. The closely related syndrome cyclic neutropenia is characterized by recurrent episodic neutropenia accompanied by symptoms including infection. Understanding the genetic etiology of congenital neutropenia can help to direct therapy, guide surveillance and health maintenance strategies, and contribute to our understanding of basic neutrophil biology. Although mutations in ELANE are the most frequent cause of congenital neutropenia, there is a wide and ever-growing list of additional causative variants. Additionally, there appears to be regional genetic variability. For example, mutations in HAX1 are rarely if ever observed in North America while they are more common in Europe. We undertook exome sequencing of a large cohort from the Severe Chronic Neutropenia International Registry (SCNIR) of North America in an effort to define the genetic spectrum of congenital neutropenia and aid in the discovery of new pathogenic variants. We expanded our previously reported study of whole exome sequencing to include 152 cases of chronic neutropenia, comprised of 94 cases of SCN and 58 cases of cyclic neutropenia. We selected cases in which ELANE testing was negative, or in a small minority of cases, where ELANE testing had not yet been performed. Indeed, exome sequencing only identified 7 cases (5 SCN and 2 cyclic) carrying pathogenic ELANE mutations in this cohort. In the remaining 145 cases, we analyzed exomes for the presence of variants in genes previously associated with congenital neutropenia including AK2, AP3B1, CD40LG, CLPB, CSF3R, CXCR2, CXCR4, DNAJC21, DNM2, DOCK2, EFL1, EIF2AK3, ELANE, G6PC3, GATA1, GATA2, GFI1, GINS1, HAX1, IRAK4, JAGN1, KAT6A, KRAS, LAMTOR2, LYST, MYD88, PGM3, PSTPIP1, RAB27A, RAC2, SBDS, SEC61A1, SLC37A4, SMARCD2, SRP54, STK4, TAZ, TCIRG1, TCN2, TLR8, USB1, VPS13B, VPS45, WAS, WDR1 and WIPF1. Pathogenic heterozygous mutations of CLPB that localize to the ATP-binding pocket were identified in 7 cases, making it the second most common cause of congenital neutropenia in North America. We additionally identified 4 cases with G6PC3 pathogenic variants, and one case each with pathogenic variants in JAGN1, CXCR4 (the cause of WHIM syndrome), germline homozygous CSF3R, and GFI1. Interestingly, we identify 2 unrelated individuals (one with SCN and one with cyclic) and 2 siblings with SCN all of whom possess a recently described heterozygous variant in SRP54 (p.T117del). We collected genomic DNA from the affected mother of the 2 siblings, an additional unaffected sibling, and the unaffected grandparents. Through this kinship, we can confirm the de novo appearance of this variant in the second generation and demonstrate that it tracks with disease status (Figure 1). We also identified 2 unrelated individuals with SRP54 variants affecting residue 175 also located within the GTPase domain (p.G175E or p.G175del). Both variants are absent from the gnomAD database, and studies are underway to demonstrate de novo acquisition. In summary, we have defined the spectrum of mutations present in ELANE-wildtype chronic neutropenia cases in North America. Pathogenic or likely pathogenic variants were identified in 26 out of 145 (18%) cases. The most frequently mutated genes were of CLPB, SRP54, and G6PC3, while mutations in HAX1 were not seen. Importantly, some of these mutations are associated with genetic syndromes with extra-hematopoietic findings (for example, CLPB and SRP54) that would warrant additional evaluations and targeted health maintenance. These findings emphasize the importance of sending large panels for genotyping, rather than targeted ELANE testing. Figure 1 Figure 1. Disclosures Bolyard: X4 Pharmaceuticals: Research Funding. Makaryan: Emendo Biotherapeutic: Research Funding. Dale: X4 Pharmaceuticals: Consultancy, Honoraria, Research Funding.

Pediatric-type nodal follicular lymphoma (PTNFL) is a variant of follicular lymphoma (FL) characterized by limited-stage presentation and invariably benign behavior despite often high-grade histological appearance. It is important to distinguish PTNFL from typical FL in order to avoid unnecessary treatment; however, this distinction relies solely on clinical and pathological criteria, which may be variably applied. To define the genetic landscape of PTNFL, we performed copy number analysis and exome and/or targeted sequencing of 26 PTNFLs (16 pediatric and 10 adult). The most commonly mutated gene in PTNFL was MAP2K1, encoding MEK1, with a mutation frequency of 43%. All MAP2K1 mutations were activating missense mutations localized to exons 2 and 3, which encode negative regulatory and catalytic domains, respectively. Missense mutations in MAPK1 (2/22) and RRAS (1/22) were identified in cases that lacked MAP2K1 mutations. The second most commonly mutated gene in PTNFL was TNFRSF14, with a mutation frequency of 29%, similar to that seen in limited-stage typical FL (P = .35). PTNFL was otherwise genomically bland and specifically lacked recurrent mutations in epigenetic modifiers (eg, CREBBP, KMT2D). Copy number aberrations affected a mean of only 0.5% of PTNFL genomes, compared with 10% of limited-stage typical FL genomes (P < .02). Importantly, the mutational profiles of PTNFLs in children and adults were highly similar. Together, these findings define PTNFL as a biologically and clinically distinct indolent lymphoma of children and adults characterized by a high prevalence of MAPK pathway mutations and a near absence of mutations in epigenetic modifiers.

Atypical chronic myeloid leukemia (aCML) is a rare subtype of myelodysplastic/myeloproliferative neoplasm (MDS/MPN) largely defined morphologically. It is, unclear, however, whether aCML-associated features are distinctive enough to allow its separation from unclassifiable MDS/MPN (MDS/MPN-U). To study these 2 rare entities, 134 patient archives were collected from 7 large medical centers, of which 65 (49%) cases were further classified as aCML and the remaining 69 (51%) as MDS/MPN-U. Distinctively, aCML was associated with many adverse features and an inferior overall survival (12.4 vs 21.8 months, P = .004) and AML-free survival (11.2 vs 18.9 months, P = .003). The aCML defining features of leukocytosis and circulating myeloid precursors, but not dysgranulopoiesis, were independent negative predictors. Other factors, such as lactate dehydrogenase, circulating myeloblasts, platelets, and cytogenetics could further stratify MDS/MPN-U but not aCML patient risks. aCML appeared to have more mutated RAS (7/20 [35%] vs 4/29 [14%]) and less JAK2p.V617F (3/42 [7%] vs 10/52 [19%]), but was not statistically significant. Somatic CSF3R T618I (0/54) and CALR (0/30) mutations were not detected either in aCML or MDS/MPN-U. In conclusion, within MDS/MPN, the World Health Organization 2008 criteria for aCML identify a subgroup of patients with features clearly distinct from MDS/MPN-U. The MDS/MPN-U category is heterogeneous, and patient risk can be further stratified by a number of clinicopathological parameters.

Severe congenital neutropenia (SCN) is an inborn disorder of granulopoiesis characterized by severe chronic neutropenia from birth, premature death secondary to infectious complications, and transformation to myeloid malignancy. Although many cases of SCN are associated with mutations in ELANE, encoding the neutrophil elastase, roughly one-third of cases do not have an identifiable genetic cause. In collaboration with the Severe Chronic Neutropenia International Registry (SCNIR), we performed exome sequencing on 90 cases of congenital neutropenia. Heterozygous missense mutations of CLPB were identified in six patients with SCN. None of these patients had mutations in other genes known to cause SCN. A total of 5 different mutations were identified that clustered within the ATPase domain. Of note, all of these mutations were predicted to be functionally deleterious and had a frequency of Prior studies showed that biallelic mutations of CLPB are associated with a syndrome defined by 3-methylglutaconic aciduria (3-MGA), cataracts, neurologic disease, and variable neutropenia. In our original cohort of 6 SCN patients with heterozygous CLPB mutations, 3-MGA was not present in the three cases where urine samples were available and none had reported cataracts. In total, 3 had neurologic abnormalities (2 seizures and 1 developmental delay). Of note, the CLPB mutations present in syndromic cases were distinct from those seen in our SCN cohort, and none of the mutations in our series are biallelic. CLPB encodes for caseinolytic peptidase B, a protein implicated in protein folding in bacteria and yeast but with an unknown role in human granulopoiesis. Based on these observations, we hypothesize that CLPB is required for normal basal granulopoiesis and that the heterozygous CLPB mutations identified in our study act in a dominant-negative fashion to disrupt granulopoiesis. To test this hypothesis, two complementary genetic approaches were employed. First, we used CRISPR-Cas9 gene editing to generate null mutations in CLPB in human cord blood-derived CD34+ hematopoietic stem/progenitor cells (HSPCs). Using this approach, we are able to achieve greater than 90% editing efficiency as assessed by next generation sequencing. The genetically modified HSPCs were cultured for 14 days under conditions that promote granulocytic differentiation. Modified HSPCs were also seeded into methylcellulose cultures to measure CFU-G. The percentage and absolute number of mature granulocytes, but not early granulocytic precursors (promyelocytes and myelocytes), were significantly reduced in cultures of gene-edited cord blood CD34+ cells. Moreover, the frequency of edited cells decreases over time in our culture system indicating that CLPB-knockout cells have a competitive disadvantage. A significant decrease in CFU-G also was observed. Second, we generated lentivirus expressing all 5 of the neutropenia-associated heterozygous CLPB mutations identified in our SCN cohort (N496K, E557K, R561G, R603H, and R620C). Expression of all of these mutants (except R603H) in cord blood-derived CD34+ cells was associated with a significant decrease in mature neutrophils and corresponding increase in early granulocytic precursors. These four CLPB mutants also resulted in a decrease in CFU-G. Collectively, these data strongly suggest that heterozygous mutations of CLPB are a new cause of congenital neutropenia. Indeed, in the North American population, CLPB mutations appear to be the second most common cause of congenital neutropenia, behind ELANE mutations. Studies are underway to examine the molecular mechanisms by which mutant CLPB disrupts granulopoiesis. Disclosures Dale: Coherus: Consultancy; Beheringer/Ingelheim: Consultancy; Athelas: Equity Ownership; Amgen: Consultancy, Research Funding; Sanofi Aventis: Consultancy, Honoraria; Cellerant: Other: Scientific Advisory Board; Hospira: Consultancy; Prolong: Consultancy; x4pharma: Consultancy, Honoraria, Research Funding.

Introduction: Acute undifferentiated leukemia (AUL) is a rare type of acute leukemia that shows no evidence of differentiation along any lineage. Clinical, immunophenotypic and genetic data is limited: the largest study to date reported 16 AUL cases but did not use the current WHO classification and included limited genetic data on 5 cases (Ann Hematol 2013 92:747-758). Moreover, it is uncertain if AUL is biologically distinct from acute myeloid leukemia with minimal differentiation (AML MD), which also shows limited myeloid marker expression and has been reported to have a poor prognosis. Methods: A total of 95 cases (36 AUL cases 59 AML MD) were identified from pathology databases of eight academic institutions with available diagnostic flow cytometric data, cytogenetic findings, and clinical data by searching for diagnoses of "AUL" or "AML MD". Diagnosis of AUL required absence of any lineage-defining markers including MPO, CD19 and CD3. Using the WHO classification, diagnosis of AML with MD required expression of at least 2 myeloid markers (CD117, CD13 or CD33), absence of myeloid maturation (CD15) or monocytic markers (CD64, CD11b, lysozyme or non-specific esterase). Next generation sequencing with extensive mutational panel data was available in 78 cases. Outcome analysis for overall survival (OS) and relapse-free survival (RFS) and were performed using Kaplan Meier and log rank test for patients who received induction chemotherapy. Results: Based on cytogenetic abnormalities (N=27) or history of MDS (N=2), according to the 2016 WHO Classification, 28 cases (6 AUL and 22 AML MD) were re-classified as AML with myelodysplasia related changes (AML MRC). The remaining 30 AUL patients presented with similar age, blood counts, bone marrow cellularity, and blast percentage as the 37 AML MD patients (all p > 0.05). Comparison of immunophenotype in the two groups showed that AUL blasts had more frequent expression of TdT (p=0.0003) and lacked myeloid markers (CD117, CD13 or CD33 p0.05) were seen between these two groups. The frequency of abnormal karyotype was similar between AUL and AML MD (16/30 [53%] vs 15/37 [41%], respectively). The most common mutations identified in AUL were PHF6 (7/18), SRSF2 (7/18), RUNX1 (7/23), ASXL1 (6/23) and BCOR (5/16). Compared to AML MD, AUL cases were characterized by frequent mutations in PHF6 (7/18 vs 1/23, p=0.013) and SRSF2 (7/18 vs 2/22 p=0.028). Limiting AUL cases to only those with 1 myeloid marker or less also showed similar findings with more frequent mutations in PHF6 (7/16 vs 1/25, p=0.0031), SRSF2 (6/15 vs 3/26 p= 0.018) and trend towards higher BCOR frequency (5/15 vs 2/26, p=0.078) in AUL patients as compared to AML MD. RUNX1 mutation was seen in 7/23 AUL and 8/29 AML MD (p>0.05). 19/30 AUL patients received induction chemotherapy (AML-type regimen in 18 cases and an ALL-type regimen in 1 case) and 15/30 achieved complete remission. In 10 AUL patients who relapsed, 9 showed identical immunophenotype and one case showed expression of CD13 and CD33. Outcome data in the subset of patients who received induction showed no difference in OS, RFS, or rates of complete remission between AUL and AML MD groups (p>0.05). The 28 AML MRC cases that were originally classified as AUL or AML MD presented with lower WBC (p=0.026), more frequent abnormal karyotype (27/28) specifically complex karyotype (20/28 p=0.002), frequent TP53 mutations (p=0.0002) when compared to the AUL group. AML MRC patients showed worse overall OS (p=0.029) as compared with AUL patients and a trend toward worse outcome as compared with AML MD (p=0.068). Conclusions: In this largest series to date, AUL group shows distinct characteristics from AML MD, including more frequent PHF6 and SRSF2 mutations and expression of TdT. However, clinical outcome is similar between the two groups in patients treated with induction chemotherapy. Cases reclassified as AML-MRC had shorter survival compared to de novo AUL and trend towards worse outcome when compared to AML MD patients. These results suggest a genetic rationale for the separation of AUL as a distinct entity from AML MD and also support the WHO classification of cases with history of prior MDS and/or MDS-type karyotype findings as AML-MRC. Disclosures Garcia: Celgene: Consultancy.

Introduction. The majority of SMZLs display an indolent course, however the disease is still incurable and a significant proportion of patients (~25-30%) experience poor outcomes surviving 5 years, and for whom tumor material collected before initiation of medical therapy was available. Mutation analysis was performed by CAPP-seq targeted deep next generation sequencing of tumor genomic DNA. A stringent bioinformatic pipeline was applied to suppress the background noise allowing to call variants with a sensitivity of 5x10-2 in FFPE derived DNA. Copy number variations (CNVs) were identified by using the sequencing reads-based GATK4-CNV algorithm. IGHV rearrangements were obtained by using LymphoTrack® IGH FR1 Assay Panel kit. Molecular clusters were identified by an iterative algorithm that maximizes genetic distinctiveness of subgroups by reassigning patients between clusters that are created a priori based on the co-occurrence of genetic lesions. Relative survival, defined as the ratio between actuarial survival observed in the SMZL cohort and expected survival of the general population matched to patients by geographical origin, sex, age and calendar year of diagnosis, was calculated using the Ederer II method. Results. The analysis included 303 patients with a SMZL diagnosis confirmed on spleen histology. The sample size allowed to identify 30% differences in survival for molecular subgroups comprising at least 5% of cases with a statistical power between 80-100%. Median follow-up was 9.2 years. At 10 years, 85% of patients were alive, consistent with the known indolent behavior of this lymphoma. Genes recurrently affected by non-synonymous somatic mutations in >10% of SMZL included KLF2 (24%), NOTCH2 (19%), KMT2D (15%), TNFAIP3 (13%), EP300 and TP53 (10%). Deletion 7q was documented in 25% of cases and IGHV1-2*04 usage in 32%. By cluster analysis, three major molecular subgroups were identified, each of them characterized by a NOTCH pathway mutated gene (Fig. 1A). The first cluster was defined by NOTCH2 and/or KLF2 mutations and was enriched in TNFAIP3 mutations and IGHV1-2*04 gene usage (Fig. 1A). The second cluster was defined by SPEN mutations, and was enriched in KMT2D and other epigenetic gene mutations (Fig. 1A). The third cluster was enriched in NOTCH1 mutations (Fig. 1A). By relative survival analysis, the NOTCH2/KLF2 cluster showed a lower survival compared to the matched general population, indicating a significant impact of the disease on patients' expected survival (Fig. 1B). Conclusions. The large sample size and inclusion of SMZL confirmed by spleen histopathology review allowed for precise estimation of the prevalence of KLF2 and NOTCH2 mutations in this lymphoma. Three molecular clusters were identified in SMZL, each of them containing a NOTCH pathway gene, supporting the relevance of NOTCH signaling in the pathogenesis of SMZL. Patients belonging to the NOTCH2/KLF2 cluster had a lower relative survival compared to the matched general population. Disclosures Traverse-Glehen: Astra Zeneca: Other: Travel; Takeda: Research Funding. Gomes da Silva:Roche: Other: Institution's payment for consultancy, Travelling support; BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: lecture fees; Celgene: Other: Travelling support; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: lecture fees, Institution's payment for consultancy, Travelling support; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: lecture fees; Gilead Sciences: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: lecture fees, Research Funding. Ladetto:Celgene: Honoraria; Jannsen: Honoraria; Acerta: Honoraria; Abbvie: Honoraria; Sandoz: Honoraria; Roche: Honoraria. Rambaldi:Pfizer: Consultancy; Novartis: Consultancy; Omeros: Consultancy; Italfarmaco: Consultancy; Amgen Inc.: Consultancy; Roche: Consultancy; Celgene: Consultancy. Vitolo:Takeda: Speakers Bureau; Sandoz: Speakers Bureau; Gilead: Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Zinzani:MSD: Honoraria, Speakers Bureau; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; SERVIER: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; TG Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; PFIZER: Honoraria, Membership on an entity's Board of Directors or advisory committees; Merck: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Speakers Bureau; Bayer: Membership on an entity's Board of Directors or advisory committees; TG Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celltrion: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda: Membership on an entity's Board of Directors or advisory committees; PFIZER: Honoraria, Membership on an entity's Board of Directors or advisory committees; Verastem: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Merck: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astra Zeneca: Speakers Bureau. Gaidano:Roche: Consultancy, Honoraria; Gilead: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Morphosys: Honoraria; Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria. Salles:Servier: Honoraria; Abbvie: Honoraria; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria; Amgen: Honoraria; BMS: Honoraria, Other: Advisory Board; Celgene: Honoraria, Other: Advisory Board, Research Funding; Acerta: Honoraria; Janssen: Honoraria, Other: Advisory Board; Merck: Honoraria; Pfizer: Honoraria; Morphosys: Honoraria; Gilead: Honoraria, Other: Advisory Board; Epizyme: Honoraria; Servier: Honoraria, Other: Advisory Board; Takeda: Honoraria. Zucca:Celltrion: Consultancy; AstraZeneca: Consultancy.

Introduction: ALL is a rare disease. Older adults with ALL have a markedly poor prognosis and higher mortality that may be attributable in part to greater comorbidity and lower use of intensive therapeutic options. Limited data are available about the real-world treatment patterns of elderly ALL patients in the US including their likelihood of receiving chemotherapy. In this study, we described treatment patterns in a population-based cohort of older adults with ALL. Methods: Using 100% Medicare ALL data from 2007-2012, we identified adults age ≥ 66 years diagnosed with ALL from 2008-2011 who were continuously enrolled in Medicare Part A and B for 12 months before ALL diagnosis (baseline period) and had Part D coverage for ≥ 30 days after diagnosis. Presence of ALL was defined by ≥1 Part A inpatient (IP)/skilled nursing facility (SNF)/home health agency (HHA)/hospice (HS) or ≥2 Part A outpatient (OP)/Part B (PB) claims carrying an ALL diagnosis code on different dates in any 2-month interval. The date of ALL diagnosis was defined as the earlier date of the 1st IP/SNF/HHA/HS claim or the 2nd of 2 OP/PB claims carrying an ALL code. Baseline comorbidity level was defined using a modified Charlson Comorbidity Index (CCI). During the follow-up period, from diagnosis to the earliest of death, disenrollment from Part A, B, and D coverage, enrollment in an HMO, or December 31, 2012, we identified chemotherapy by presence of a claim containing billing codes for a specific chemotherapy agent or chemotherapy administration; use of tyrosine kinase inhibitors (TKI) was identified by the presence of corresponding National Drug Codes within Part D pharmacy claims. We defined chemotherapy course from the first claim within 90 days of diagnosis until the last claim with a < 60-day gap between two consecutive claims for chemotherapy. Baseline patient characteristics and treatment patterns were described. Chi-square test was used to assess the differences in baseline characteristics between treatment groups. Kaplan-Meier method was used to estimate the median overall survival (OS) and the 95% confidence interval (CI) from treatment initiation. Results: Of 727 patients who met study inclusion criteria, 235 (32%) received treatment with only chemotherapy within 90 days of ALL diagnosis, 51 (7%) with chemotherapy and TKI, and 17 (2%) with only TKI. Chemotherapy-treated patients with or without TKI were younger and had lower comorbidity burden compared with patients not receiving chemotherapy (P Among 286 (39%) chemotherapy-treated patients regardless of TKIs, the median (interquartile range [IQR]) time to chemotherapy initiation was 3 (0-11) days. Chemotherapy was administered in 209 (73%) patients in an inpatient setting with mean (SD) length of stay 22.9 (13.9) days; of these, 90 (43%) received chemotherapy only in an inpatient setting within the first chemotherapy course. There were 177 (62%), 74 (26%), and 35 (12%) patients who received 1, 2, and ≥3 chemotherapy courses, respectively, for a total of 450 chemotherapy courses with median (IQR) course duration of 53.5 (22-137) days. Overall, 68 (9%) patients had a TKI prescription filled within 90 days of diagnosis; of these, 19%, 32%, and 49% were aged 66-69, 70-74, and ≥ 75 years, respectively; 57% were female; and 79% were white. The median (IQR) time to first prescription fill date was 20 (12-34) days. Imatinib was more common as the first TKI agent (n=55; 81%) than dasatinib (n=13; 19%). In total, 20 (29%) patients switched TKI agents; of these, 16 (80%) switched from imatinib to dasatinib. Conclusions: Among elderly Medicare beneficiaries diagnosed with ALL in 2008-2011, 39% were treated with chemotherapy and 9% were prescribed a TKI within 90 days of diagnosis. Patients with advanced age and higher comorbidity level were less likely to receive chemotherapy. Median OS was 10 months for patients with only chemotherapy, 18 months for patients with chemotherapy and TKI, and 6 months for patients with only TKI. These findings demonstrate the unmet need for safe and effective treatments for elderly ALL patients. Further studies assessing the comparative effectiveness and benefit-risk of treatments are warranted. Disclosures Chia: Amgen Inc: Employment, Equity Ownership. Katz:Amgen Inc: Employment, Equity Ownership.

Introduction: Acute lymphoblastic leukemia (ALL) is a very rare disease with a poor prognosis in elderly (>65 years) adult patients. Prognosis is worse in patients who have relapsed or refractory ALL (R/R ALL). Because there is limited real-world data on elderly patients with R/R ALL, we aimed to describe patient characteristics and treatment patterns among these patients in a large population-based dataset. Methods: Using 100% Medicare ALL administrative claims data from 2007-2012, we identified patients aged ≥ 66 years who were newly diagnosed with ALL in 2008-2011, continuously enrolled in Medicare fee-for-service (FFS) for 12 months prior to ALL diagnosis date, and continuously enrolled with Medicare Part D coverage for at least 30 days after diagnosis. Presence of ALL was defined as ≥1 Part A inpatient (IP)/skilled nursing facility (SNF)/home health agency (HHA)/hospice (HS) claim or ≥2 Part A outpatient (OP)/Part B (PB) claims occurring on different dates in any 2-month interval with an ICD-9 diagnosis code for ALL; date of ALL diagnosis was defined as the earlier date of the 1st IP/SNF/HHA/HS claim or the 2nd of 2 OP/PB claims carrying an ALL code. Follow-up for R/R disease began after the ALL diagnosis date, and was limited to a cohort of patients who had also received chemotherapy or a tyrosine kinase inhibitor (TKI) within 90 days of the ALL diagnosis date. Patients were identified as having R/R ALL if they had one of the following criteria: 1) a claim with an ICD-9 diagnosis code for R/R ALL (204.02) in any position after treatment was initiated; 2) use of clofarabine, nelarabine or the start of a second chemotherapy course; or 3) a change in type of TKI identified from Part D prescription drug claims. The date of R/R ALL diagnosis was defined as the earliest of date a patient met any of the R/R ALL criteria. Patient characteristics and treatment patterns were described for patients identified as having R/R ALL. Results: Of the 303 patients who were identified as having ALL from 2008-2011 and had treatment with chemotherapy or TKI within 90 days of the ALL diagnosis date, 144 patients (48%) were identified as subsequently having R/R disease. Of those, 39 (27%) were identified through diagnosis code only, 40% were identified through treatment changes only, and 47 (32%) were identified through both diagnosis codes and treatment changes. The median time from the ALL diagnosis date to date of R/R disease was 201 days, 172.5 days, and 240 days for patients identified using diagnosis codes, treatment changes, and both diagnosis codes and treatment changes, respectively. Overall, 81 (56%) patients with R/R ALL defined at the changes in treatment with or without a subsequent diagnosis. Patients who were identified with R/R ALL were slightly younger and had fewer comorbidities than the overall group of patients diagnosed with ALL (Table). Of the patients identified with R/R ALL, 126 (88%) were treated with any chemotherapy or TKIs; 120 (83%) patients were treated with chemotherapy and 26 (18%) patients were treated with TKIs. Eleven (8%) patients received a bone marrow/stem cell transplant. Of the 120 patients treated with chemotherapy, 73% had only one chemotherapy course and 51% had the first chemotherapy administration in an outpatient setting. Vincristine alone or in combination with other agents was the most commonly observed type of chemotherapy. Of the 26 patients who were treated with TKIs, 42% had only one course and 69% were treated with dasatinib. Conclusions: These data describe real-world patient characteristics and treatment patterns in elderly patients with R/R ALL. Approximately half of the elderly ALL patients who were treated for ALL within 90 days of diagnosis were identified as having R/R ALL through administrative claims data, and more than half were identified through changes in treatment and not through the use of diagnosis codes. Thus, we are likely underestimating the true proportion of elderly ALL patients who have R/R disease. Interestingly, we observed that 51% of patients treated with chemotherapy had the first chemotherapy administration in an outpatient setting, and that only 8% of patients received a bone marrow/stem cell transplant. Disclosures Chia: Amgen Inc: Employment, Equity Ownership. Katz:Amgen Inc: Employment, Equity Ownership.

Pediatric-type nodal follicular lymphoma (PTNFL) is a variant of follicular lymphoma (FL) characterized by localized presentation and excellent behavior despite its often high-grade histologic appearance. We recently identified high proliferation index and the absence of BCL2, BCL6, and IRF4 gene rearrangements as defining features of PTNFL in both children and adults (Louissaint, Blood 2012). In contrast to typical FL, children with PTNFL consistently have persistent remissions after surgical excision alone. Therefore, it is critically important to identify PTNFL in order to avoid unnecessary therapy. Considering the unique clinical behavior of PTNFL, we hypothesized that the mutational landscape of this disease would differ from that of typical FL. Twenty-four cases were collected from several institutions (MGH, Brigham & Women's, Weill Cornell, Chicago Children's, Boston Children's, University of Pittsburgh, SUNY Downstate, and Stanford). PTNFL was defined by the following criteria: 1) nodal involvement, 2) architectural effacement by a clonal follicular proliferation, 3) high proliferation index and 4) absence of both MUM1/IRF4 expression and BCL2/BCL6 rearrangements by FISH. All cases presented with localized nodal involvement and demonstrated no evidence of recurrence or progression after chemotherapy (n=5), radiation (n=3) or surgical excision alone (n=13) (therapeutic approach to be confirmed in 3 cases), with a median follow-up of 33.1 months (range 10-124 months). Subjects ranged in age from 4-60 years, including 14 children (4-18 years; median 15) and 10 adults (20-60 years; median 29.5). Whole exome sequencing performed on 7 PTNFL cases showed a strikingly low mutation burden (7.1 non-silent mutations/exome), more than an order of magnitude lower than the exomic mutation burden of typical FLs (Green, PNAS 2015; Pasqualucci, Cell Rep 2015). Given these findings, we pursued targeted exome capture and next-generation sequencing for 112 genes previously reported to be recurrently mutated in FL across a panel of 20 PTNFLs. Targeted sequencing (mean depth, 250) again demonstrated very low mutation burden in PTNFL, with a median number of non-silent mutations of 1.67/case compared with 4 mutations/case (P Disclosures South: Lineagen Corporation: Consultancy; ARUP Laboratories: Employment; Affymetrix: Consultancy, Honoraria; Illumina: Consultancy, Honoraria. Hasserjian:Promedior: Consultancy.

Background: ITP is a rare disorder characterized by low platelet counts and a tendency toward increased bleeding and bruising. Several studies have shown that ITP incidence increases with age. Elderly ITP patients may have a higher risk of bleeding and their disease management can be challenging due to increased burden of other health problems. However, little information is available regarding rates of BREs in elderly ITP patients. As the population ages, understanding the frequency of bleeding events and/or use of ITP therapy to treat or prevent bleeding in routine clinical practice could provide insights into the real-world burden of this disease in elderly patients. Methods: Using Medicare 20% sample data 2007-2012, we identified elderly Medicare fee-for-service (FFS) enrollees newly diagnosed with primary ITP (ICD-9-CM diagnosis code 287.31) at age ≥67 years (to ensure ≥2 years of Medicare FFS enrollment before their first claim with an ITP code to determine study eligibility), between January 1, 2009, and September 30, 2012. BREs were defined as ≥1 bleeding event (of any severity) and/or use of ITP therapies commonly considered for rescue or emergency therapy (platelet transfusion, intravenous immunoglobulin [IVIg], anti-D, or IV steroids). Claims with relevant codes with dates of service separated by ≤3 days were considered a single BRE. The rate of BREs (per person-year) was calculated for all BREs and by event type incorporated into BREs for the ITP cohort overall and stratified on ITP phase (newly diagnosed: 0 to 12 months). ITP phase was defined based on ITP disease duration, which was calculated as the time between initial ITP diagnosis and last ITP claim. Patients were followed from ITP diagnosis until the last ITP claim (end of ITP duration), death, disenrollment from FFS coverage, or December 31, 2012, whichever came first. Results: We identified 3007 elderly patients with primary ITP (mean [SD] age: 79.6 [7.5] years; 55% female) in the database of 12.8 million enrollees. The median (IQR) ITP duration was 6 (1, 17) months; 37%, 30%, and 34% of patients had ITP duration 12 months, respectively. During 2687 person years follow-up, 1806 patients (60%) experienced at least one BRE for a total of 6305 BREs; 42% were bleeding events only, 50% were therapy only, and 8% were both. BRE rates (95% CI) per person year were 2.35 (2.29-2.41) for any BREs and 0.99 (0.95-1.03), 1.18 (1.14-1.22), and 0.18 (0.16-0.20) for BREs with bleeding only, therapy only, and both, respectively. The most common bleeding types were gastrointestinal hemorrhage, hematuria, epistaxis, and ecchymoses. Intracranial hemorrhage was reported in 107 patients (3.6%). Newly diagnosed patients had higher BRE rates (Table). Table.Newly diagnosed ITP (n=3007)Persistent ITP (n=1907)Chronic ITP (n=1010)BREsCountRate per person year (95% CI)CountRate per person year (95% CI)CountRate per person year (95% CI)All24474.46 (4.28,4.63)21962.05 (1.96,2.14)16621.56 (1.49,1.64)With bleeding only10871.98 (1.86,2.10)8350.78 (0.73,0.83)7330.69 (0.64,0.74)With therapy only10221.86 (1.75,1.98)12621.18 (1.11,1.24)8840.83 (0.78,0.88)With both bleeding and therapy3380.62 (0.55,0.68)990.09 (0.07,0.11)450.04 (0.03,0.05) Conclusion: We provided current real-world estimates of BRE rates in elderly patients with ITP. About 60% of ITP patients experienced at least one BRE, and half of all BREs were defined by therapy use alone. This demonstrates the importance of examining both bleeding and use of rescue or emergency ITP therapy in the assessment of disease burden in elderly patients with ITP. Disclosures Cetin: Amgen, Inc: Employment, Equity Ownership. Wasser:Amgen, Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Altomare:Amgen Inc.: Consultancy, Honoraria.

This study investigated the immature platelet fraction (IPF) in assessing treatment effects in immune thrombocytopenia (ITP). IPF was measured on the Sysmex XE2100 autoanalyzer. The mean absolute-IPF (A-IPF) was lower for ITP patients than for healthy controls (3.2 vs 7.8 × 109/L, P < .01), whereas IPF percentage was greater (29.2% vs 3.2%, P < .01). All 5 patients with a platelet response to Eltrombopag, a thrombopoietic agent, but none responding to an anti-FcγRIII antibody, had corresponding A-IPF responses. Seven of 7 patients responding to RhoD immuneglobulin (anti-D) and 6 of 8 responding to intravenous immunoglobulin (IVIG) did not have corresponding increases in A-IPF, but 2 with IVIG and 1 with IVIG anti-D did. This supports inhibition of platelet destruction as the primary mechanism of intravenous anti-D and IVIG, although IVIG may also enhance thrombopoiesis. Plasma glycocalicin, released during platelet destruction, normalized as glycocalicin index, was higher in ITP patients than controls (31.36 vs 1.75, P = .001). There was an inverse correlation between glycocalicin index and A-IPF in ITP patients (r2 = −0.578, P = .015), demonstrating the relationship between platelet production and destruction. Nonresponders to thrombopoietic agents had increased megakaryocytes but not increased A-IPF, suggesting that antibodies blocked platelet release. In conclusion, A-IPF measures real-time thrombopoiesis, providing insight into mechanisms of treatment effect.

Background: Febrile neutropenia (FN) and hospitalizations for infection are serious potential complications of myelosuppressive chemotherapy (chemo) treatment in cancer patients. Primary prophylactic G-CSF (PPG) is often used to decrease incidence of FN in patients at high risk. Due to the potential for G-CSF to stimulate neutrophil precursors at the same time as myelosuppression from chemotherapy, it is recommended that G-C SF be administered 24 hours after chemo administration. In addition, several studies showed that use of G-CSF on the same day as chemo may result in worse FN outcomes. Data are limited describing practice patterns of PPG timing relative to chemo administration in elderly patients with non-Hodgkin's lymphoma (NHL), overall and by agent. Methods: The study population included non-HMO enrollees in the 20% Medicare sample with Parts A and B coverage who had NHL and initiated the first course of chemo between July 1, 2007, and November 30, 2011. PPG was defined as G-CSF initiated during days 0-5 of the first cycle, with day 0 the start of the chemo course. In patients with PPG, type of agent prescribed [Filgrastim (FIL), Sargramostim (SAR), or Pegfilgrastim(PEG)], timing of PPG initiation relative to chemo start date overall and by agent, and duration of prophylactic use (for the daily use agents FIL and SAR) were examined. Counts and percentages were estimated. Results: The study cohort included 13,402 patients with NHL; 2690 (20.1%) received PPG. In these patients, the most common PPG agent used was PEG (2471; 91.9%) followed by FIL (171; 6.4%) and SAR (48; 1.8%). The median [interquartile range] of course duration (in days) for the daily use agents was 3.5 [2, 5] for FIL and 3 [1.5, 5] for SAR. Overall, first G-CSF use within the prophylactic period peaked on the day after chemo initiation (day 1, 47.3%) and steadily decreased from day 2 (22%) to day 5 (4%). About 5% of patients received PPG on the same day as chemo (day 0). Patterns were similar by agent type (Figure). More PPG with FIL than with PEG was used on days 4 and 5. Conclusion: Use of prophylactic growth factor support is the recommended standard of care for patients at high risk of neutropenic infection. Consistent with the recommendations, PPG began most often on the day after chemo initiation regardless of agent type and more PPG with FIL started on day 4 or 5 after chemo initiation. Figure 1 Figure 1. Note: Ten or fewer patients with SAR on days 0, 3-5. Results are not shown. Disclosures Page: Amgen Inc.: Employment, Equity Ownership. Barron:Amgen Inc.: Employment, Equity Ownership. Morrow:Amgen Inc.: Employment, Equity Ownership. Stryker:Amgen Inc.: Employment, Equity Ownership. Acquavella:Amgen Inc.: Employment, Equity Ownership. Collins:ZS Pharma Inc.: Consultancy; Keryx Biopharmaceuticals, Inc.: Consultancy; Amgen Inc.: Consultancy; NxStage Medical Inc.: Consultancy.

Human herpesvirus 8 (HHV-8)/Kaposi sarcoma–associated herpesvirus (KSHV) is linked to a number of malignancies thought to be driven by cytokines, including interleukin-6 (IL-6). Rta, a transcriptional activator encoded by HHV-8/KSHV, activates the viral lytic cycle leading to the expression of several viral genes implicated in viral pathogenesis. However, the effect of HHV-8/KSHV Rta on cellular genes has not been reported. We present evidence that the human IL-6(hIL-6) gene is up-regulated by Rta. Rta potently activated (up to 164-fold) the hIL-6 promoter in a dose-dependent manner in a transient transfection reporter system. Rta also induced expression of the endogenous hIL-6 gene, as shown by enzyme-linked immunosorbent assays. Activation of the hIL-6gene by HHV-8/KSHV supports the role of hIL-6 in the development of these malignancies.

Introduction TRAs increase platelet counts by stimulating the TPO-receptor. A known effect of TRA treatment is increased bone marrow fibrosis (MF). This study explored extent of MF, its clinical relevance, and incidence of phenotypic or karyotypic abnormalities in TRA-treated ITP patients. Methods This single-center study was carried out at the Platelet Disorders Center of Weill Cornell Medical College (WCMC), NY, USA. Eligibility criteria were: diagnosis of ITP; treatment with a TRA (romiplostim, eltrombopag, AKR 501 (Eisai) or Shionogi agent), ≥ 1 bone marrow biopsy (BMB) performed during TRA treatment. BMBs were performed every 1–2 years as standard f/u procedure for our ITP patients on TRA. MF grade was assessed from MF-0 to MF-3 according to the European Consensus Grading System in 141 BMBs acquired prior to (n=15), during (n=117) and after (n=9) TRA-treatment from 66 patients. Fifty disease-free staging BMBs served as controls. BMBs were separately reviewed by 3 pathologists to assess the grade of MF and then reviewed concurrently as needed to reach consensus. The study was approved by the IRB of WCMC; informed written consent was obtained from patients. Results Median (Q1-Q3) age at the time of 1st BMB was 38 years (18-63); 34 males 32 females. 32 patients had > 2 on-treatment BMBs. The distribution of MF-grades is shown in the figure. The proportion of MF-0 decreased from 67% in pretreatment biopsies (BM0) to 21% in the first set of BMBs (BM1); in the 15 patients with pre- and on-treatment BMBs there was a significantly higher number of MF-0 in BM0 as compared to BM1 (10/15 vs. 3/15;p=0.016) suggesting that TRAs induce fibrosis in treated patients. In patients with multiple on-treatment BMBs (n=32), first on-treatment BMB was graded as MF-1 in 24. In the last set of biopsies (BM-Last) 8 had progressed to MF-2/3, 12 remained MF-1, and 4 became MF-0 illustrating the unpredictability of the future course of MF from the first on-treatment marrow. Nonetheless, a higher number of MF-2/3 BMB was found in BM-Last as compared to BM1 [10 (31%) vs. 3 (9%) of 32; p=0.039]. In 5 patients with MF-2/3 BMB, TRA were discontinued: on f/u 2 had less fibrosis, 1 remained the same, and 2 are awaiting f/u BMB. BMB was graded MF-0 in 54% and MF-1 in 46% of control BMB; no difference was found in the proportion of MF-0/1 and 2/3 in BM0 compared to controls, but increased MF-2/3 was seen in BM-last compared to controls (p Of the following 6 clinical factors: age, duration of disease, duration of treatment, splenectomy status, type and dose of agent; only age was significantly higher in patients with MF-2/3 as opposed to MF0/1 at time of BM-last [57 vs. 38 years; p=0.01]. There was a tendency toward longer duration of treatment in patients with MF-2/3 as compared to MF-0/1 (3.6 y vs. 2.7y; p=0.16). Flow cytometric immunophenotyping of BMB in 89 examinations did not reveal emergence of clonal abnormalities. Cytogenetic analysis in 72 BMBs did not show any clonal karyotypic abnormalities. Conclusions This large single center experience indicates that TRAs induce some degree of MF as supported by: 1) decreasing fraction of MF-0 after initiation of TRA, 2) decreasing fraction of MF-0/1 (normal grades of MF) in subsequent on-treatment BMBs, 3) increasing fraction of MF-2/3 (pathological grades) in patients with multiple on-treatment BMBs. Only older age was associated with higher grades of fibrosis. However, MF remained stable in most patients within the range found in normal individuals. Higher grades of MF (MF-2/3) observed in some patients were not clinically significant based on peripheral blood counts. Overall, since a number of patients developed MF-2 and even MF-3, this suggests a risk of progressive fibrosis in approximately 20% of patients. No neoplastic immunophenotypic or karyotypic abnormalities emerged during treatment with TRAs. Annual or bi-annual follow-up with BMB should be carefully considered in TRA-treated patients. Discontinuation of TRA should be encouraged in those who develop/progress to MF-3 and possibly even MF-2 to avoid potential further progression of MF Disclosures: Bussel: Amgen: Equity Ownership, Membership on an entity’s Board of Directors or advisory committees, Research Funding; GlaxoSmithKline: Equity Ownership, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Cangene: Research Funding; Genzyme: Research Funding; IgG of America: Research Funding; Immunomedics: Research Funding; Ligand: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Eisai: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Shionogi: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Sysmex: Research Funding; Symphogen: Membership on an entity’s Board of Directors or advisory committees.