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Background: Immune thrombocytopenia (ITP) is the most common cause of acquired immune platelet destruction in children. Clinical symptoms range from asymptomatic to significant and even life-threatening bleeding, fatigue, and reduced health-related quality of life. About 75% of affected children experience spontaneous remission, with the remainder developing chronic ITP. Our clinical observations suggest a decreased prevalence of ITP among Black children, although no available studies have evaluated racial or ethnic predisposition to ITP or to chronic disease. We hypothesized that biological differences in Black children alter the prevalence of ITP, relative to the general population, and may affect disease course. Methods: A retrospective analysis evaluating race and ethnicity of all children with ITP treated at Texas Children's Hospital (TCH, Houston, TX) from January 2015-July 2019 was performed, and compared to both the Houston metropolitan area and the TCH Cancer Center 2018 race and ethnicity data. Of the 699 unique patients, race and ethnicity data were unavailable for 24, and 2 patients were excluded (1 with leukemia, 1 with bone marrow failure). The remaining patients were categorized as (1) White, non-Hispanic; (2) Black, non-Hispanic; (3) Hispanic; and (4) Other. Hispanic patients included those who self-identified as (1) White, Hispanic; (2) Black, Hispanic; (3) Asian, Hispanic; (4) Multi-race, Hispanic; and (5) Unknown race, Hispanic. Demographic data was then collected in a second ITP population derived from the Children's Hospital of Philadelphia (CHOP, Philadelphia, PA) and the surrounding metropolitan area. To match the distribution reported in the Houston metro area data, a comparison was conducted focusing on the proportion of Black non-Hispanic patients in each cohort. A chi-squared test with Yates correction was utilized to compare nonparametric categorical data using GraphPad Prism version 8.0.1 for Windows, GraphPad Software, San Diego, California, USA. A p-value of Results: At TCH, there were 673 evaluable ITP patients. Classifying by race only, 42 were Black (6.2%), 564 White (83.8%), and 67 Other (Asian, Mixed Race, Native American, 9.9%). There was a significantly smaller percentage of ITP patients identified as Black, non-Hispanic (n= 40, 5.9%) relative to both the Texas Children's Cancer Center (16% Black, non-Hispanic) and the Houston metropolitan area populations (16% Black, non-Hispanic, p Conclusions: This analysis suggests a significant difference in the prevalence of ITP by race in children at two large tertiary care centers in the US. We found that Black children were less likely to develop ITP but those who did were more likely to develop chronic disease relative to other races. Race and ethnicity data at both institutions more closely matched their surrounding metropolitan areas, suggesting the observed differences are not due to care or access barriers. These findings support the possibility that damaging genetic variants, altered gene expression and/or other biological differences in immune response may lead to increased risk of ITP in White children, or protective factors result in reduced prevalence of ITP in Black children. Further research to explore these differences is ongoing. Figure Disclosures Lambert: CSL Behring: Consultancy; Amgen: Consultancy, Other; Bayer: Other: Ad boards; Novartis: Other: Ad boards, Research Funding; Shionogi: Consultancy; Kedrion: Consultancy; Sysmex: Consultancy; AstraZeneca: Research Funding; PDSA: Research Funding. Despotovic:Dova: Honoraria; Novartis: Research Funding; Amgen: Research Funding.

Introduction: Tyrosine kinase inhibitors (TKI) are overall well tolerated in chronic myeloid leukemia (CML) s, but more than 30% require dose reduction or change to another TKIs due to intolerance. Impact of TKI dose-reduction on outcomes in a "real world" setting is unknown, thus, we evaluated the characteristics and outcomes of chronic phase (CP)-CML patients who received doses of TKI lower than the label/FDA recommendation. Method: CP-CML with at least 12 months of follow-up, with ISBCR/ABL1 available after dose reduction were selected. Last TKI was defined as TKI which were taken at the last follow up visit or before disease progression to accelerated (AP) or blast phase (BP). FDA approved doses of imatinib (IM), dasatinib (DAS), nilotinib (NIL), bosutinib (BOS), and ponatinib (PON) were 400mg, 100mg, 600mg (300mg BID), 500mg, and 45mg, respectively . Results: Between January 2005 and April 2016, 173 CP-CML patients, started IM (75%), DAS (18%) NIL (5%) and PON, BOS on clinical trial in 2%. Overall Fifty-eight (33.5%) patients had TKI dose reduction. IM (n=15) dose was reduced to 75% (range, 25-75), DAS (n=15) to 50% (range, 20-80), NIL (n=15) to 50% (range, 13-67), BOS (n=15) to 80% (range, 40-80) and PON (n=15) to 33% (range, 33-67). Median age for patients that received dose-reduced TKI was 55 (range, 18-88), and 27% received > 3 prior TKIs. With a median follow up of 53.6 (range 13.4-183.7) months, only 1 progressed to AP, and none to BP. Overall 60% achieved MMR. Among 35 patients who achieved MMR before dose reduction, MMR was maintained in 25 (71.4%) for a median of 17.2 (2-97.9) months from dose-reduction. CMR was achieved in patients on a maintenance dose of IM, 100mg QD (n=8); DAS, 20mg QD (n=4); NIL 300mg QD (n=3) and BOS, 200mg QD (n=3). Conclusion: Similar to data reported from clinical trials, TKI dose reduction appears to be safe and associated with high response rates. This data confirms that the minimal effective dose for each TKI remains to be defined. Disclosures Heffner: Pharmacyclics: Research Funding; AbbVie: Research Funding; Millennium: Research Funding; Celgene: Research Funding. Jillella:Leukemia Lymphoma Society: Research Funding. Kota:Ariad Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Leukemia Lymphoma Society: Research Funding; Incyte: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees.