Abstracts Clinical Lymphoma, Myeloma & Leukemia September 2023 S396 JAK inhibitors 12.8 months (range, 2.3–72.9). No dose-limiting toxicities occurred. The most common treatment-related adverse events (TRAEs) included grade 1-2 nausea, vomiting, and diarrhea. No hematologic TRAEs reported. Spleen volume reduction (SVR) observed in 8 of 10 evaluable patients (median best change -13%, range -3% to -42%, 2 patients showed ≥35% SVR). TSS improvements observed in 9 of 10 evaluable patients (median best change -70%, range -31% to -100%; 6 patients showed ≥50% total symptom score [TSS] response). Broad cytokine reduction observed (eg, IL-6, IL-8, IL-10, EN-RAGE). At week 12, patients with higher cytokine reductions correlated with higher TSS improvement. BMF improved in 1 patient who achieved spleen and symptoms responses and showed reductions in MF associated cytokines: IL6 (68%), IL12p40 (83%), MMP9 (56%), and EN-RAGE (68%) and is on active treatment for more than 18 months. Enrollment is ongoing. Conclusions: Preliminary data showed TP-3654 may prompt early cytokine changes that may correlate with symptoms response; SVR, TSS improvement, and BMF reduction; TP-3654 is well tolerated with no myelosuppressive TRAEs. Keywords: MPN, Pim1, TP3654, myelofibrosis, cytokine, phase I MPN-470 Examining Racial Disparities in Primary Myelofibrosis Incidence and Survival Rates: A SEER Database Analysis from 2000–2019 M Bakri Hammami MD1,2, Charan Vegivinti MD1, Rahul Thakur MD1, Asma Qasim MD3, Amit Verma MD4, Swati Goel MD4 1Jacobi Medical Center/Albert Einstein College of Medicine, New York, USA. 2Mayo Clinic, Rochester, USA. 3Cleveland Clinic Abu Dhabi, Abu Dhabi, UAE. 4Montefiore Medical Center, New York, USA Background: Primary myelofibrosis (PMF) is an aggressive subtype of BCR-ABL negative myeloproliferative neoplasms characterized by bone marrow fibrosis and clonal proliferation. The racial differences among patients with PMF are not defined. Methods: Retrospective analysis of the incidence, sociodemographic characteristics, and survival of patients with primary myelofibrosis using the Surveillance, Epidemiology and End Results (SEER) database from 2000–2019 was conducted. IBM SPSS V.23 was utilized for data analysis. Results: The study included 5,198 patients diagnosed with PMF, of whom 60.0% were male (n=3,120), with a median age at diagnosis of 69±13 years (Range 1–98). Black patients accounted for 8.3% (n=431) of the study population, while 82% were white (n=4262) and 9.7% were other races (n=505). The ageadjusted incidence rate (95% CI) of PMF was 0.32 (0.31–0.33) cases per 100,000 person-years. The annual percentage change (APC) significantly increased during the study period (2000– 2019) (APC=3.8%, 95% CI 2.5%–5.15%, P<0.05). Blacks had a significantly younger mean age at diagnosis than non-blacks (63.6 vs 68.6, P<0.001). A higher proportion of black patients were unmarried (57.6% vs 34.8%, P<0.001, c2 = 76.8) and female (47.8% vs 39.3%, P=0.001, c2 = 11.97) compared to non-blacks. Median income was also lower for black patients (P<0.001). Complications of PMF, including leukemic transformation, were the leading cause of death in the study population (n=1941, 37.3%), followed by cardiac diseases (n=337, 6.5%), pulmonary diseases (n=170, 3.3%), and GI diseases (n=67, 1.3%). Estimated overall survival was 69% and 41% at 2- and 5- years, respectively. Cox regression analysis showed that worse survival was significantly associated with higher age (HR = 1.050, 95% CI = 1.046–1.053, P<0.001), male sex (HR = 1.367, 95% CI = 1.269–1.482, P<0.001), black race (HR = 1.348, 95% CI = 1.176–1.545, P<0.001), and being unmarried (HR = 1.178, 95% CI = 1.090–1.273, P<0.001). Conclusions: This study highlights the potential impact of socio-racial factors on outcomes in primary myelofibrosis. It underscores the need to address the underlying factors contributing to these disparities to ensure that all patients with PMF have equitable access to high-quality care. Keywords: MPN, primary myelofibrosis, SEER, myeloproliferative disorders, racial disparities, survival MPN-498 Addition of Navitoclax to Ruxolitinib for Myelofibrosis Patients With Relapsed/ Refractory Disease and Suboptimal Response to Ruxolitinib Monotherapy: REFINE Cohort 1 Dose Escalation and Expansion Naveen Pemmaraju MD1, Tim C.P. Somervaille MBBS, PhD2,3, Francesca Palandri MD, PhD4, Rami S. Komrokji MD5, Andrew Perkins PhD6, Rosa M. Ayala Diaz MD, PhD7, David Lavie PD8, Akihiro Tomita MD, PhD9, Yang Feng PhD10, Qin Qin PhD10, Brenda Chyla PhD10, Akshanth R. Polepally PhD10, Jalaja Potluri MD10, Jacqueline S. Garcia MD11 1The University of Texas MD Anderson Cancer Center, Houston, USA. 2The Christie NHS Foundation Trust, Manchester, United Kingdom. 3Cancer Research UK Manchester Institute, Manchester, United Kingdom. 4Institute of Hematology and Medical Oncology “Lorenzo and Ariosto Seràgnoli”, St. Orsola-Malpighi Hospital, University of Bologna, Bologna, Italy. 5Moffitt Cancer Center, Tampa, USA. 6Australian Centre for Blood Diseases, Monash University, Melbourne, Australia. 7Hospital Universitario 12 de Octubre, Madrid, Spain. 8Hadassah-Hebrew University Medical Center, Jerusalem, Israel. 9Fujita Health University School of Medicine, Toyoake, Japan. 10AbbVie Inc, North Chicago, USA. 11Dana-Farber Cancer Institute, Boston, USA Context: Navitoclax (oral BCL-XL/BCL-2 inhibitor) is being evaluated in a phase 2 study (REFINE, NCT03222609) in patients with myelofibrosis (MF). Historically, outcomes in patients with relapsed /refractory (R/R) MF were poor. This pooled analysis of navitoclax plus ruxolitinib presents safety and efficacy in patients with R/R MF in REFINE Cohort 1. Methods: Patients had suboptimal responses to ruxolitinib after ≥12 weeks (1a, escalation) or ≥24 weeks (1b, expansion) and were on stable ruxolitinib doses of ≥10mg twice daily. Patients in Cohort 1a started with 50mg/ day navitoclax, with a stepwise increase to ≤300mg provided the platelet count was ≥75×109/L. In Cohort 1b, patients received
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