Abstracts Clinical Lymphoma, Myeloma & Leukemia September 2023 S398 years, in agreement with international findings. While JAK2 V617F mutation analysis has grown into an integral part of the diagnosis algorithm and workup of patients recognized under the category of MPN at SGHUMC, clinical data to categorize patients are still missing. Lebanon has suffered a hat-trick of simultaneous events between 2020 and 2022—the economic crisis, the Beirut blast, and the COVID-19 pandemic—which have greatly affected the collection of clinical information, the variety of available tests, and patients’ capabilities to cover test expenses. Further studies aiming to correlate the percentage of the mutant allele with clinical information and to extend the analysis to other relevant driving genes, such as exon 12 JAK2 mutations, calreticulin genes, and MPL, are becoming an emergent need for refinement of the molecular diagnostic workup as well as for prognosis and management of the disorders, especially in the era of precision medicine. Keywords: myeloproliferative neoplasm, JAK2 V617F mutation MPN-512 Inpatient Resource Utilization and Costs Associated With Hospitalizations for Thromboembolic Events Among Patients With Polycythemia Vera Jingbo Yu MD, PhD1, Julie Gayle MPH2, Ning Rosenthal MD, MPH, PhD2, Harold Brown MBA, MHA2, Evan Braunstein MD, PhD1 1Incyte Corporation, Wilmington, DE, USA. 2PINC AI™ Applied Sciences, Premier Inc., Charlotte, NC, USA Context: Patients with polycythemia vera (PV) have increased risk of thromboembolic events (TEs); little is known about healthcare resource utilization (HCRU) and costs associated with TE hospitalizations in PV. Objective: To describe HCRU and costs for TE-related hospitalizations among patients with PV. Design and Patients: Adults with inpatient discharge January 1, 2017, through June 30, 2020, with PV and venous thromboembolism (VTE) and/or arterial thromboembolism (ATE) were identified from chargemaster data from the PINC AI™ Healthcare Database (PHD; includes 25% of US inpatient discharges). Main Outcome Measures: HCRU and costs of TE-related hospitalizations at first (index) TE hospitalization and for 2 years after index discharge. Results: In 3494 patients (ATE, 69.2%; VTE, 27.1%; both, 3.7%; men, 59%; White, 81%) from 623 hospitals, mean (SD) age was 70.7 (14.0) years; 73% had Medicare primary insurance. Mean (SD) Charlson Comorbidity Index was 3.2 (2.3). The most common TEs were ischemic stroke (46%), myocardial infarction (25%), deep vein thrombosis (23%), and pulmonary embolism (13%). During index TE hospitalization, mean (SD) hospital length of stay (LOS) was 7 (9) days; mean (SD) hospitalization cost was $24 403 ($38 577), exceeding the average cost in a medically ill (nonsurgical) cohort with VTE (n=376 858; range, $15 814–$20 282) in a prior PHD study. One-third were admitted to the intensive care unit (ICU), with a mean (SD) ICU LOS of 5 (7) days and mean (SD) ICU cost of $29 342 ($42 890). Risk of TE-related readmission increased with follow-up length (30-day, 6%; 90-day, 10%; 1-year, 16%; 2-year, 20%). Mean (SD) TE-related readmission costs increased over time (30-day, $19,334 [$26,666]; 2-year, $29,531 [$37,936]). Mean (SD) cost for index hospitalization and 2-year TE-related readmissions was $30,285 ($43,883). All-cause in-hospital mortality during index hospitalization was 6% (patients with both VTE/ ATE, 12%), with an additional 5% (patients with both VTE/ATE, 12%) within 2 years after index hospitalization. Conclusions: TErelated hospitalizations among patients with PV were associated with substantial HCRU, costs, and mortality. Average hospitalization cost was greater than that observed in general medically ill patients with VTE, highlighting the complexity of this population and the importance of TE prevention in PV management. Sponsorship: Incyte Corporation. Keywords: MPN, polycythemia vera, thrombotic events, ischemic stroke MPN-524 Reductions in Indolent Systemic Mastocytosis Biomarker Burden With Avapritinib in the Registrational, Double‑Blind, Placebo‑Controlled PIONEER Trial Jason Gotlib MD, MS1, Mariana Castells MD, PhD2, Hanneke Oude Elberink MD, PhD3, Frank Siebenhaar PD Dr med4,5, Karin Hartmann MD6,7, Sigurd BroesbyOlsen MD8, Tracy I. George MD9, Jens Panse MD10,11, Iván Alvarez-Twose MD, PhD12, Deepti H. Radia MRCPI, FRCPath13, Tsewang Tashi MD14, Cristina Bulai Livideanu MD, MSc15, Vito Sabato MD, PhD16, Paul Van Daele MD, PhD17, Sonia Cerquozzi MD18, Ingunn Dybedal MD, PhD19, Andreas Reiter MD20, Celalettin Ustun MD21, Philippe Schafhausen MD22, Prithviraj Bose MD23, Daniel J. DeAngelo MD, PhD24, Lindsay Rein MD25, Pankit Vachhani MD26, Massimo Triggiani MD, PhD27, Mark Rafferty MBChB, BSC, MRCP, FRCPath28, Nauman M. Butt MBChB, MRCP, FRCPath, MD29, Stephen T. Oh MD, PhD30, Friederike Wortmann MD31, Johanna Ungerstedt MD, PhD32, Minakshi Taparia MD33, Andrew T. Kuykendall MD34, Cecilia Arana Yi MD, MSHS35, Mattias Mattsson MD, PhD36, William Shomali MD1, Matthew P. Giannetti MD37, Ilda Bidollari MD, MBA38, Hui-Min Lin PhD38, Robyn Scherber MD38, Maria Roche MS38, Cem Akin MD, PhD39, Marcus Maurer MD4,5 1Stanford Cancer Institute/Stanford University School of Medicine, Stanford, CA, USA. 2Department of Medicine, Division of Allergy and Clinical Immunology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA. 3Department of Allergology, University Medical Center, Groningen Research Institute Asthma and COPD, University of Groningen, Groningen, Netherlands. 4Institute of Allergology, Charité–Universitätsmedizin Berlin, Corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany. 5Fraunhofer Institute for Translational Medicine and Pharmacology ITMP, Allergology and Immunology, Berlin, Germany. 6Division of Allergy, Department of Dermatology, University Hospital Basel and University of Basel, Basel, Switzerland. 7Department of Biomedicine, University Hospital Basel and University of Basel, Basel, Switzerland. 8Department of Dermatology and Allergy Centre,
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