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Lessons from extinction can be used in trials designed to pursue a cure for cancer. When cancer cannot be cured, similar strategies may be unwise, and strategies that leverage the adaptations of cancer to therapy should be considered.

BackgroundPrimary immunodeficiency is common among patients with autoimmune cytopenia.ObjectiveThe purpose of this study is to retrospectively identify key clinical features and biomarkers of primary immunodeficiency (PID) in pediatric patients with autoimmune cytopenias (AIC) so as to facilitate early diagnosis and targeted therapy.MethodsElectronic medical records at a pediatric tertiary care center were reviewed. We selected 154 patients with both AIC and PID (n=17), or AIC alone (n=137) for inclusion in two cohorts. Immunoglobulin levels, vaccine titers, lymphocyte subsets (T, B and NK cells), autoantibodies, clinical characteristics, and response to treatment were recorded.ResultsClinical features associated with AIC-PID included splenomegaly, short stature, and recurrent or chronic infections. PID patients were more likely to have autoimmune hemolytic anemia (AIHA) or Evans syndrome than AIC-only patients. The AIC-PID group was also distinguished by low T cells (CD3 and CD8), low immunoglobulins (IgG and IgA), and higher prevalence of autoantibodies to red blood cells, platelets or neutrophils. AIC diagnosis preceded PID diagnosis by 3 years on average, except among those with partial DiGeorge syndrome. AIC-PID patients were more likely to fail first-line treatment.ConclusionsAIC patients, especially those with Evans syndrome or AIHA, should be evaluated for PID. Lymphocyte subsets and immune globulins serve as a rapid screen for underlying PID. Early detection of patients with comorbid PID and AIC may improve treatment outcomes. Prospective studies are needed to confirm the diagnostic clues identified and to guide targeted therapy.

Autoimmune Lymphoproliferative Syndrome (ALPS), commonly caused by mutations in the FAS gene, is a disease with variable penetrance. Subjects may be asymptomatic, or they may present with lymphadenopathy, splenomegaly, cytopenias, or malignancy. Prompt recognition of ALPS is needed for optimal management. We describe a multi-generational cohort presenting with clinical manifestations of ALPS, and a previously unreported heterozygous missense variant of uncertain significance in FAS (c.758G >T, p.G253V), located in exon 9. Knowledge of the underlying genetic defect permitted prompt targeted therapy to treat acute episodes of cytopenia. This cohort underscores the importance of genetic testing in subjects with clinical features of ALPS and should facilitate the reclassification of this variant as pathogenic.

Background Advances in risk stratification have improved the 3-year disease-free survival (DFS) and overall survival (OS) of low-risk pediatric acute myeloid leukemia (LR-AML) to approximately 70 % and 85 % respectively. LR-AML is defined by favorable cytogenetic/molecular features and/or optimal early response to therapy. However, cumulative anthracycline exposure in contemporary Children’s Oncology Group (COG) regimens approach a doxorubicin equivalent exposure of 540 mg/m2; with rates of non-infection related left ventricular systolic dysfunction (LVSD) approaching 15 %. This is a major cause of toxicity in these patients and precludes the further use of anthracyclines in the relapsed setting; therefore, strategies that reduce cardiotoxicity while maintaining excellent outcomes are needed. Patients and methods Twenty-seven pediatric patients with LR-AML were treated with an anthracycline-reduced approach (Aflac-AML regimen) between 2011 and 2016. Patients received four courses of therapy including three high-dose cytarabine containing courses and a cumulative doxorubicin equivalent exposure of 390 mg/m2, a 28 % reduction in anthracycline dosing compared to current COG regimens. Results The 3-year DFS and OS was 70.0 % and 85.5 % respectively, from end of Induction I (first chemotherapy cycle) with a median follow-up of 3.2 years. These survival outcomes are comparable to current LR-AML regimens. Only two patients developed non-infection related LVSD during therapy and more importantly, none developed LVSD after completion of therapy. Conclusion These findings suggest that LR-AML outcomes can be maintained using a reduced anthracycline chemotherapy regimen, resulting in lower cardiac toxicity. This new chemotherapy backbone is now being tested prospectively (NCT04326439) to further validate its use in pediatric LR-AML.

BackgroundHigh-risk non-CNS pediatric malignant solid tumors (pMST) have unsatisfactory outcomes, and novel therapies are warranted. Adoptive cellular therapy (ACT) using tumor-infiltrating lymphocytes (TIL) has produced durable responses in melanoma, and improvements in TIL expansion have made ACT-TIL feasible for other solid tumors.1–3 Preclinical mouse models suggest that T-cells from bone marrow (marrow-infiltrating lymphocytes, MIL) have antitumor reactivity offering another source for ACT.4 5 To demonstrate feasibility of ACT in pMST we hypothesized that TIL/MIL can be expanded from these patients.MethodsPatients ≤21 years old undergoing standard-of-care pMST resection were enrolled on an IRB approved protocol. Fresh tumor (≥1 cm3) was collected and bone marrow (10 mL) was obtained when accessible from standard of care procedures. TIL/MIL were cultured in media containing IL-2 (6000 IU/mL). TIL were expanded from tumor fragment cultures (TFC, >1 mm3) or tumor digest. Select TIL samples were further expanded using a rapid expansion protocol (REP). Phenotype of expanded TIL (CD3, CD4, CD8 and CD56) was evaluated using flow cytometry. IFN- γ secretion, measured by ELISA assay, measured tumor-specific reactivity after co-culture with autologous tumor and TIL.ResultsTwenty samples were obtained between March 2019-May 2021. Two samples were ineligible (final pathology not pMST), leaving 18 samples for analysis. Five marrow samples were collected. TIL were expanded from 14/18 samples (78%) through TFC with median 5.17 x 10^6 cells (range 1.86 x 10^6–3.21 x 10^8). Average phenotype (%) of TFC-TIL were CD3 (63.17), CD4 (21.46), CD8 (46.19) and CD56 (32.68). 9/10 (90%) of samples successfully underwent REP with median 9.35 x 10^7 cells(range 2.49 x 10^7–5.86 x 10^8) final viable TIL and average fold-change 718.6 (median 458.6). Average phenotype (%) of post-REP TIL were CD3 (96.04), CD4 (75.04), CD8 (19.17) and CD56 (0.43). TIL were expanded from TFC of therapy-naïve (8/10, 80%) and pretreated (chemotherapy and checkpoint immunotherapy) samples (5/8, 63%). Seven samples had sufficient tissue to test tumor-specific reactivity; all were non-reactive. MIL pre-REP was expanded from four samples with median 9.55 x 10^6 cells (range 8.00 x 10^5–1.00 x 10^7). Average phenotype of expanded MIL (%) were CD3 (45.17), CD4 (24.46), CD8 (36.15) and CD56 (28.21) (table 1).Results of TIL and MIL expansion from 18 pMST samples. Abbreviations: Dx: diagnosis, pre-REP: pre-rapid expansion protocol, post-REP: post-rapid expansion protocol, PBMC: peripheral blood mononuclear cells, GNB: ganglioneuroblastoma, WT: Wilms tumor, OS: osteosarcoma, NB: neuroblastoma, IMT: inflammatory myofibroblastic tumor; ASPS: alveolar soft part sarcoma, SS: synovial sarcoma, ERMS: embryonal rhabdomyosarcoma, N: no systemic therapy, C: chemotherapy, I: immunotherapy, DNG: did not grow, N/A: not applicable, NR: non-reactiveAbstract 178 Table 1Expansion of TIL from pMSTConclusionsThis study demonstrates feasibility of pMST TIL expansion ex vivo. Due to tissue volume constraints inherent in pMST sampling, anti-tumor reactivity testing was not feasible for most patients. Determining optimal strategy for TIL-ACT in pMST will require further investigation regarding techniques for expanding tumor-specific TIL.AcknowledgementsThe authors would like to thank Swim Across America (www.swimacrossamerica.org) and the Ocala Royal Dames (www.ocalaroyaldames.org) for their generous support of this work.ReferencesRosenberg SA, Restifo NP. Adoptive cell transfer as personalized immunotherapy for human cancer. Science 2015;348(6230):62–68.Hall M, Mullinax JE, Royster E, et al. Expansion and characterization of tumor-infiltrating lymphocytes from human sarcoma. Journal of Immunotherapy of Cancer 2015;3(Suppl. 2):19.Mullinax JE, Hall M, Beatty M, et al. Expanded tumor-infiltrating lymphocytes from soft tissue sarcoma have tumor-specific function. J Immunother 2021;44(2):63–70.Feuerer M, Beckhove P, Bai L, et al. Therapy of human tumors in NOD/SCID mice with patient-derived reactivated memory T cells from bone marrow. Nat Med 2001;7(4):452–458.Feuerer M, Rocha M, Bai L, et al. Enrichment of memory T cells and other profound immunological changes in the bone marrow from untreated breast cancer patients. Int J Cancer 2001;92(1):96–105.Ethics ApprovalThis study was approved by the Johns Hopkins All Children’s Hospital IRB (#IRB00193453). Consent was obtained from the patient or parent, as appropriate for age, prior to participating in this study.

TPS11577 Background: Several sarcomas possess chromosomal translocations in FET family members ( FUS, EWSR1, and TAF15) responsible for cancer development. Sarcomas caused by FET family gene rearrangements include ES, desmoplastic round cell small tumors (DSRCT), myxoid liposarcoma (ML), and several others. Lysine specific demethylase 1 (LSD1) is a critical protein for sarcoma development and progression through its colocalization and/or association with several FET family oncogenic transcription factors. This suggests that pharmacologic inhibition of LSD1 may be a therapeutic strategy. Seclidemstat (SP-2577, Salarius Pharmaceuticals) is an oral, first-in-class, small molecule with reversible, noncompetitive inhibition of LSD1 (IC50: 25–50 nM). In vitro and in vivo data demonstrate seclidemstat, or analogs, modulate EWS/ETS transcriptional activity, down-regulating oncogene expression and up-regulating tumor-suppressor gene expression, leading to significant tumor growth inhibition in ES mouse xenograft studies. Seclidemstat has shown in in vitro ES cell lines near additivity efficacy when added to TC. In in vitro studies of other FET-translocated sarcomas, including ML (FUS/DDIT3 fusion) and clear cell sarcoma (EWS/ATF1 fusion), seclidemstat showed anti-proliferative activity. In an ongoing Phase 1 trial investigating single agent seclidemstat in advanced solid tumors (NCT03895684), three pts with metastatic FET-translocated sarcomas had a median progression-free survival of 5.7 months (range: 4.3–7.2) with a best response of stable disease despite having a median of 5 (range: 1–7) prior therapies. Methods: This dose expansion Phase 1 study (NCT03600649) assesses seclidemstat at 900 mg PO BID, the recommended Phase 2 dose, in two expansion cohorts: a single agent expansion in select sarcoma pts (n = 30) and a safety lead-in dose escalation and expansion (n = 24) of seclidemstat combined with TC in pts with ES. Pts must be ≥12 years old, have ECOG performance status of 0 or 1, with a life expectancy > 4 months. In the select sarcoma cohort, pts must have ML (n = 15) or other sarcomas with FET family translocations (n = 15) including DSRCT. One to 3 prior lines of therapy are allowed. In the ES combination cohort, up to 2 lines of prior therapy are allowed. Primary objective is safety/tolerability and secondary objective is efficacy. The trial is currently recruiting across 8 locations in the United States. Clinical trial information: NCT03600649.

11514 Background: Ewing sarcoma (ES), a rare bone and soft tissue sarcoma mainly of adolescents and young adults, is characterized by a chromosomal translocation resulting in a fusion oncoprotein. Lysine specific demethylase 1 (LSD1) has been shown to associate with the fusion oncoprotein and promote oncogenic transcriptional activity making LSD1 an attractive target for ES treatment. Seclidemstat is a novel, selective, reversible oral LSD1 inhibitor capable of inhibiting both LSD1’s catalytic and scaffolding functions. This is the first report of an LSD1 inhibitor in a Phase 1 trial focused exclusively on ES. Methods: SALA-002-EW16 is a Phase 1 trial of single agent seclidemstat in patients (pts) with relapsed or refractory (R/R) ES. This report describes the completed monotherapy dose escalation. Pts > 12 years received oral SP-2577 twice daily in 28-day cycles under fasting conditions at the assigned dose level. The primary objective was safety and tolerability. Secondary objectives include to determine maximum-tolerated dose (MTD), recommended Phase 2 dose (RP2D), preliminary efficacy, pharmacokinetics, and pharmacodynamics. Results: As of December 30, 2020, 27 pts with R/R ES were enrolled. Pts received escalating doses of SP-2577 at 75 (n = 1), 150 (n = 2), 300 (n = 4), 600 (n = 6), 900 (n = 8), or 1200 mg PO BID (n = 6). The median age was 25 years (range 15–68), 63% were male, and pts had received a median of 3 (range 2–12) prior systemic therapies. There were no treatment-related deaths. The most common ( > 5%) grade 3 treatment-related adverse events (TRAEs) were vomiting (15%), abdominal pain (11%), and hypokalemia (11%). One pt (4%) with grade 3 pancreatitis reported a grade 4 AE of elevated lipase. All remaining grade 3 TRAEs, including hematological TRAEs, were reported in only one pt each. Four pts discontinued study for an AE (weight loss, pancreatitis, vomiting, abdominal pain). Three pts had a dose reduction. The first cycle dose-limiting toxicities were gastrointestinal-related AEs observed in 2 pts at 1200 mg BID. Thus, the MTD/RP2D was established as 900 mg BID. Peak plasma concentrations occurred at a median of 4 hours (h) post-dose and median terminal half-life was 6 h; exposure was dose proportional through 900 mg BID. One pt at 600 mg BID achieved a reduction in target lesions starting at end of C2 with further target lesion tumor shrinkage through end of C4 and C6 (maximum 76% tumor shrinkage) with coincident new non-target lesion appearance at end of C2. Of pts evaluable for response at the end of C2 (12 pts), two additional pts (16.7%) at 600 mg BID and 900 mg BID had overall stable disease. Conclusions: Seclidemstat has a manageable safety profile with proof-of-concept preliminary activity in heavily pretreated pts with relapsed/refractory ES. These data support the planned Phase 2 expansion of seclidemstat as single agent and in combination with chemotherapy in ES and other sarcomas that share similar translocations. Clinical trial information: NCT03600649.

TPS11567 Background: Ewing sarcoma (ES) is a rare, aggressive bone and soft tissue cancer that predominantly afflicts adolescents and young adults. Novel therapeutic agents are needed as there are no approved targeted treatments for this disease. ES is characterized by a chromosomal translocation resulting in an EWS/ETS fusion oncoprotein, a transcription factor that results in aberrant gene expression leading to ES progression. Lysine specific demethylase 1 (LSD1) associates with EWS/ETS oncoproteins to alter gene expression and contribute to disease progression. Directly inhibiting EWS/ETS is challenging and little progress has been made, though targeting LSD1 presents a viable therapeutic strategy for ES. Seclidemstat (SP-2577, Salarius Pharmaceuticals) is a first-in-class, orally bioavailable, small molecule with reversible and noncompetitive selective inhibition of LSD1 at low nanomolar concentrations (IC50: 25-50 nM). Seclidemstat inhibits LSD1’s scaffolding functions and enzymatic activity to help reverse aberrant gene expression. In vitro data show that treatment with seclidemstat, or seclidemstat analog, modulates EWS/ETS transcriptional activity, down-regulating oncogene expression and up-regulating tumor-suppressor gene expression. In in vivo xenograft studies (e.g., SK-N-MC, A673), mice treated with seclidemstat show significant tumor growth inhibition/regression vs the control vehicle group. Methods: This phase 1/2 clinical study of seclidemstat is being conducted in relapsed or refractory ES (NCT03600649). The trial is an open-label, non-randomized dose-escalation/dose-expansion study designed to determine the maximum tolerated dose through single-patient dose escalation followed by traditional 3+3 design. The primary objective is to assess seclidemstat’s safety and tolerability while secondary objectives include pharmacokinetics, efficacy and exploratory pharmacodynamic markers. Patients must be ≥12 years old, have received at least 1 prior line of therapy including a prior camptothecin-based regimen, with a life expectancy > 4 months. All patients receive seclidemstat twice-daily (BID) as oral tablets until unacceptable toxicity or disease progression. Patients are followed for survival until the end of study. The trial is currently recruiting across 8 locations in the United States. Upon identification of the recommended phase 2 dose, that cohort will be expanded to enroll a total of 20 patients. Clinical trial information: NCT03600649 .

Objective: The purpose of this study is to increase awareness and improve diagnosis of primary immune deficiency (PID) in the heterogenous group of patients with autoimmune cytopenia (AIC) by identifying clinical characteristics and laboratory biomarkers that distinguish PID patients from patients with AIC alone. This is especially relevant in genetically-defined PIDs which may be resistant to conventional therapy and mechanism-based treatment approach is required. Evans syndrome, defined by multi-lineage autoantibodies (two or more positive anti-platelet, anti-neutrophil, or direct Coombs test) is a known risk factor for PID; therefore we also investigate the incidence of PID in a broad cohort of AIC patients with single and multi-lineage cytopenias. Methods: Patients with autoimmune cytopenias (autoimmune hemolytic anemia (AIHA), immune thrombocytopenia (ITP), or autoimmune neutropenia (AIN)) were referred to our Immune Dysregulation clinical team and prospectively enrolled in the study period of 2016-2019. Detailed immune phenotyping (IgG, IgA, IgM, lymphocyte subsets, vaccine titers, lymphocyte proliferation to mitogens/antigens), serum lipopolysaccharide (LPS) and autoantibodies were measured and/or collected by chart review and genetic testing for PID was pursued. Results: From 2016 to 2019, 78 patients were enrolled to our study. The patients were predominantly children (ages 1-82 years, average age 16.82 years). Of 78 patients with AIC, 48 (61%) were diagnosed with underlying PID based on immune phenotyping and/or genetic testing. Of 39 patients with genetic testing to date, 19 (49%) have been diagnosed with genetically-defined PID (pathogenic variants in CTLA-4, NFKB1, ALPS-related genes, WAS, POLE-1, PI3K, CYBB, or 22q11 [partial DiGeorge syndrome]); the remainder were classified as combined immune deficiency or common variable immune deficiency based on immune phenotyping; an additional two patients were classified as ALPS based on clinical history/flow cytometry/family history of ALPS. Lymphocyte subsets (CD4+ T, CD8+ T, CD19+ B, CD56+ NK) and immune globulins (IgG, IgA, IgM) tended to be lower in AIC-PID patients vs AIC-only (p Conclusions: An unexpectedly high fraction of patients with AIC were identified with underlying PID in our Immune Dysregulation program. Routine basic immune evaluation with immunoglobulin levels and lymphocyte subsets expedited diagnosis of PID. Genetic evaluation distinguished a group of patients with AIC-PID and highly elevated LPS level, reflecting high bacterial load, and this may distinguish them from the rest of patients with AIC. The source of bacterial LPS can be multifactorial and is yet to be determined. Our studies continue focusing on biomarkers that can be applied to the heterogenous group of patients with AIC. This will allow early detection and timely initiation of targeted therapies. Disclosures No relevant conflicts of interest to declare.

Background: Renal medullary carcinoma (RMC) is a rare, aggressive form of renal cell carcinoma almost exclusively (>90%) diagnosed in individuals with sickle cell trait (SCT), and 2/3 of those affected are male. Based on population-surveillance data, only 246 patients were diagnosed with RMC between 2005-2014 (Carden etal. J Sickle Cell Disease and Hemoglobinopathies, 2018) and many patients have metastatic disease at diagnosis (Msaeoul et al., Clin Genitourin Cancer, 2019). Median overall survival (OS) in patients with metastatic RMC (mRMC) at diagnosis is less than 12 months and predictors of survival are largely unknown, although case reports suggest novel chemotherapeutic strategies are important (Carden et al., Ped Blood Cancer, 2017&2018). The role SCT plays in RMC pathobiology, however, is largely unknown, as many patients do not have a complete hemoglobin subtype profile completed at diagnosis. Studies evaluating sickle hemoglobin concentrations (%HbS) in relation to survival for patients with RMC are needed, as SCT is associated with renal dysfunction and researchers have hypothesized that HbS polymerization within red cells traversing the kidney disrupts blood perfusion, which leads to kidney injury and an increased possibility for cancer formation (Msaeoul et al, Clin Cancer Res, 2018). Patients with %HbS≤36%, such as patients with SCT and concomitant alpha-globin gene deletion(s) might be protected against HbS polymerization and renal concentrating defects (Gupta etal., J Clin Invest, 1991). We hypothesize that lower %HbS is associated with higher survival. In this preliminary multi-institutional study, we retrospectively reviewed available charts from patients diagnosed with mRMC and SCT to evaluate for an association between %HbS and OS. Methods: We found nine patients (3 adults, 6 children) who were diagnosed with mRMC and SCT at our various institutions between 2002-2017 who had survival data. Eight patients had %HbS levels by hemoglobin quantification at diagnosis. In a post-hoc analysis, patients were separated into two groups (%HbS>36% and %HbS≤36%), levels similar to that found in patients with alpha-globin gene deletions described by Gupta et al. Fit-curves were determined for OS vs. %HbS. Three-year OS was determined using Kaplan-Meier analysis and the log-rank method. P Results: Clinical characteristics of patients are shown in Table 1. Average age (standard deviation) at diagnosis was 15.2 years (4.9) and most patients were male (87.5%). Six patients had %HbS >36% and 2 patients had %HbS ≤36%. Median OS was 17.8 months. Using fit-function testing, analysis of survival vs. %HbS yielded an exponential relationship (R2=0.69), suggesting higher survival when %HbS≤36% (p=0.05). OS of the two patients with %HbS≤36% was greater than those with %HbS>36%, though results were not statistically significant (p = 0.09). Conclusion: While there are limitations to this small, retrospective analysis, these data suggest that lower intracellular red cell %HbS concentrations could be protective in patients with mRMC and SCT. Chemotherapy and other treatment regimens may also play a role in survival and need to be studied. Further investigation is needed to determine the role SCT plays in RMC pathobiology and to determine if %HbS concentrations, as well as alpha-thalassemia deletion(s), may be protective in patients with RMC. Disclosures Carden: GBT: Honoraria; NIH: Research Funding.

10533 Background: Despite advances in risk stratification and therapy, the post-induction disease free survival (DFS) and overall survival (OS) for children with low-risk acute myeloid leukemia (LR-AML) remain low with DFS and OS of 50% and 68%, respectively, on the standard arm of the recent Children’s Oncology Group (COG) trial, AAML1031. Additionally, current therapy for pediatric LR-AML contains anthracycline doses exceeding thresholds known to increase the risk of adverse cardiac effects. In an effort to decrease exposure to cardiotoxic therapy, the Aflac Cancer and Blood Disorders Center adopted an institutional practice to treat LR-AML patients with a regimen of intensified induction therapy with decreased anthracycline exposure (Aflac-AML consisting of ADE10, Mitox/HiDAC, HiDAC/VP, Capizzi II). The aim of this study is to describe the associated toxicities and outcomes of this regimen in pediatric LR-AML. Methods: We retrospectively reviewed medical records of patients diagnosed with de novo LR-AML and treated per the Aflac-AML regimen from 2011-2014. Charts were reviewed for cardiac outcomes, ICU admissions, and the rate of infectious toxicities. DFS and OS were determined using Kaplan-Meier survival analysis. Results: We identified 11 LR-AML patients treated with Aflac-AML therapy. Patients received a planned 317 mg/m2 cumulative anthracycline dose vs 442 mg/m2for those treated on AAML1031. There was no decrease in LVEF with a mean change of +2.17% for Aflac-AML patients from the time of diagnosis to therapy completion (p = 0.23). The primary infectious toxicities observed were febrile neutropenia and bacterial infections with a median of 36.4±6% documented bacterial infections per cycle. Fungal and viral infections were rare as were ICU admissions – median 4.5±4% per cycle – and there were no toxic mortalities. The 3-year DFS and OS from end of induction I for Aflac-AML patients were 72.7% and 90.9%, respectively. Conclusions: The Aflac-AML regimen resulted in short-term toxicities and outcomes comparable to current chemotherapy regimens for pediatric LR-AML but with reduced anthracycline exposure. These data support use of this regimen for pediatric LR-AML patients.

ierra Nevada Corporation’s (SNC) Space Systems Group in Louisville, Colorado is leading an effort to create a low-cost, safe, commercial crew transportation service to and from low Earth orbit (LEO), including the International Space Station (ISS). The spacecraft, called the Dream Chaser, is a reusable lifting-body vehicle that launches vertically on top of an expendable Atlas V rocket and lands horizontally on a conventional runway. It is designed to be piloted during its primary mission to and from the ISS, but is also capable of autonomous operation (Figure 1).