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Secondary myelodysplastic syndromes and acute myeloid leukemia (sMDS/AML) are rare myeloid neoplasms in children/adolescents and have a dismal prognosis. The mainstay therapy is hematopoietic cell transplantation (HCT) but there has been little therapeutic innovation for decades and outcomes remain poor. CPX-351, a fixed 5:1 molar ratio of liposomal cytarabine/daunorubicin, has shown favorable safety and efficacy in elderly individuals with sAML and children with relapsed de novo AML, which led the FDA to recently expand the label of CPX-351 to include pediatric patients with secondary AML, however, no data has been reported in this patient group. We report the outcomes of seven young patients with newly diagnosed sMDS/AML uniformly treated with CPX-351. Five patients had previously received chemotherapy for osteosarcoma, Ewing sarcoma, neuroblastoma, or T-ALL; one had predisposing genomic instability disorder (Cornelia de Lange syndrome); and one presented with MDS-related AML and multi-organ failure. The median age at diagnosis of myeloid malignancy was 17 (13-23) years. We identified somatic mutations and copy-number changes across 16 leukemia driver genes in six cases (including TP53 in two), abnormal karyotypes in six cases and rearrangements involving MECOM or NIM1K-TERT in two patients. Additional genomic studies identified pathogenic germline mutations in CHEK2 and SMC3 each in a single patient . Patients received 1-3 cycles of CPX-351 (100 units/m 2 on days 1, 3, and 5) resulting in complete morphologic remission without overt toxicity or treatment-related mortality. This approach allowed for adding FLT3 inhibitor as individualized therapy in one patient. Six patients were alive and leukemia-free at 0.51-3.25 years after HCT. One patient died from disease progression before HCT. Concluding, CPX-351 is an effective and well-tolerated regimen for cytoreduction in pediatric secondary myeloid malignancies warranting further investigation Figure 1 Figure 1. Disclosures Triplett: Miltenyi: Other: Travel, meeting registration.

Introduction: Venetoclax is a selective BCL2 inhibitor approved for the treatment of CLL and AML in adults and is currently being evaluated in several hematologic and solid malignancies. While plasma pharmacokinetics (PK) of venetoclax is well documented, data regarding the accumulation of venetoclax into the central nervous system (CNS) are limited. Venetoclax has a molecular weight of 868.44 which was hypothesized to limit its passage through the tight junctions of the blood brain barrier (BBB). Moreover, venetoclax is a substrate of the P- glycoprotein (P-gp) and breast cancer resistance protein (BCRP) efflux transporters, expressed by endothelial cells at the BBB, which presents an extra hurdle for penetration into the CNS. In this analysis we characterized the passage of venetoclax into the CNS using PK samples collected during a phase 1 study (NCT03236857) of pediatric patients with relapsed and refractory acute leukemia receiving venetoclax in combination with chemotherapy. Methods: PK samples from cerebrospinal fluid (CSF) were collected at screening and if a lumbar puncture was performed as standard of care during treatment. Plasma PK samples were collected throughout the study. CSF and plasma concentrations of venetoclax were determined using liquid-liquid extraction followed by liquid chromatography (LC) with tandem mass spectrometric detection (MS/MS). The lower limit of quantitation for venetoclax was 2.14 ng/mL in plasma and 0.1ng/mL in CSF. Results: There was a total of 66 samples from 33 patients with relapsed or refractory AML or ALL. The venetoclax concentration in CSF ranged between Conclusion: To our knowledge this is the first study reporting venetoclax CSF pharmacokinetics in the AML and ALL setting. The lower disposition observed in humans is contrary to our expectation, given the significantly higher expression of P-gp in mice BBB compared to humans and suggests that other factors are involved in venetoclax disposition to the CSF. The ability of venetoclax to cross the blood brain barrier may explain the reported activity of venetoclax in treatment of hematologic malignancies with CNS involvement1,2. References: Reda G, Cassin R, Dovrtelova G, et al. Venetoclax penetrates in cerebrospinal fluid and may be effective in chronic lymphocytic leukemia with central nervous system involvement. Haematologica. 2019;104(5):e222-e223. doi:10.3324/haematol.2018.213157 Beziat G, Gauthier M, Protin C, et al. Venetoclax with high-dose methotrexate and rituximab seem effective and well-tolerated in the treatment of central nervous system involvement of chronic lymphocytic leukemia: A case report. Clin Case Rep. 2020;8(2):269-273. Published 2020 Jan 10. doi:10.1002/ccr3.2580 Disclosures Salem: AbbVie Inc.: Current Employment, Other: may hold stock or other options. Badawi:AbbVie Inc.: Current Employment, Other: may hold stock or other options. Place:Novartis: Consultancy, Other: Institutional Research Funding; AbbVie: Consultancy. Palenski:AbbVie: Current Employment, Other: may hold stock or other options. Arrendale:AbbVie Inc.: Current Employment, Other: may hold stock or other options. Kim:AbbVie, Inc.: Current Employment, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months, Other: may hold stock or other options. Cooper:Celgene: Other: Spouse was an employee of Celgene (through August 2019). Menon:AbbVie Inc.: Current Employment, Other: may hold stock or other options.