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Advances in the understanding of germline predisposition to pediatric cancers, particularly myeloid neoplasms, have increased rapidly over the last 20 years. Here, we highlight the most up-to-date knowledge regarding known pathogenic germline variants that contribute to the development of myeloid neoplasms in children.This discussion enumerates the most notable myeloid neoplasm-causing germline mutations. These mutations may be organized based on their molecular underpinnings-transcriptional control, splicing and signal transduction control, and a group of heterogeneous bone marrow failure syndromes. We review recent findings related to the biochemical mechanisms that predispose to malignant transformation in each condition. Key genetic discoveries such as novel mutations, degrees of penetrance, principles of the two-hit hypothesis, and co-occurrence of multiple mutations are shared. Clinical pearls, such as information regarding epidemiology, natural history, or prognosis, are also discussed. Germline mutations predisposing to pediatric myeloid neoplasms are frequent, but underrecognized. They hold major clinical implications regarding prognosis, treatment strategies, and screening for other malignancies. Further research is warranted to better characterize each of these conditions, as well as identify additional novel germline pathogenic variants of interest.

Background Large β-globin gene cluster deletions (hereditary persistence of fetal hemoglobin [Hb] or β-, δβ-, γδβ-, and ϵγδβ-thalassemia), are associated with widely disparate phenotypes, including variable degrees of microcytic anemia and Hb F levels. When present, increased Hb A2 is used as a surrogate marker for β-thalassemia. Notably, ϵγδβ-thalassemias lack the essential regulatory locus control region (LCR) and cause severe transient perinatal anemia but normal newborn screen (NBS) results and Hb A2 levels. Herein, we report a novel deletion of the ϵ, Aγ, Gγ, and ψβ loci with intact LCR, δ-, and β-regions in 2 women and newborn twins. Methods Capillary electrophoresis (CE), high-performance liquid chromatography (HPLC), DNA sequencing, multiplex ligation-dependent probe amplification (MLPA), gap-polymerase chain reaction (gap-PCR), and long-read sequencing (LRS) were performed. Results NBS showed an Hb A > Hb F pattern for both twins. At 20 months, Hb A2 was increased similarly to that in the mother and an unrelated woman. Unexplained microcytosis was absent and the twins lacked severe neonatal anemia. MLPA, LRS, and gap-PCR confirmed a 32 599 base pair deletion of ϵ (HBE1) through ψβ (HBBP1) loci. Conclusions This deletion represents a hemoglobinopathy category with a distinct phenotype that has not been previously described, an ϵγ-thalassemia. Both the NBS Hb A > F pattern and the subsequent increased Hb A2 without microcytosis are unusual. A similar deletion should be considered when this pattern is encountered and appropriate test methods selected for detection. Knowledge of the clinical impact of this new category will improve genetic counselling, with distinction from the severe transient anemia associated with ϵγδβ-thalassemia.

Supplementary methods, three supplementary tables and 16 supplementary figures

Although inhibitors of the kinases CHK1, ATR, and WEE1 are undergoing clinical testing, it remains unclear how these three classes of agents kill susceptible cells and whether they utilize the same cytotoxic mechanism. Here we observed that CHK1 inhibition induces apoptosis in a subset of acute leukemia cell lines in vitro, including TP53-null acute myeloid leukemia (AML) and BCR/ABL–positive acute lymphoid leukemia (ALL), and inhibits leukemic colony formation in clinical AML samples ex vivo. In further studies, downregulation or inhibition of CHK1 triggered signaling in sensitive human acute leukemia cell lines that involved CDK2 activation followed by AP1-dependent TNF transactivation, TNFα production, and engagement of a TNFR1- and BID-dependent apoptotic pathway. AML lines that were intrinsically resistant to CHK1 inhibition exhibited high CHK1 expression and were sensitized by CHK1 downregulation. Signaling through this same CDK2–AP1–TNF cytotoxic pathway was also initiated by ATR or WEE1 inhibitors in vitro and during CHK1 inhibitor treatment of AML xenografts in vivo. Collectively, these observations not only identify new contributors to the antileukemic cell action of CHK1, ATR, and WEE1 inhibitors, but also delineate a previously undescribed pathway leading from aberrant CDK2 activation to death ligand–induced killing that can potentially be exploited for acute leukemia treatment.Significance:This study demonstrates that replication checkpoint inhibitors can kill AML cells through a pathway involving AP1-mediated TNF gene activation and subsequent TP53-independent, TNFα-induced apoptosis, which can potentially be exploited clinically.

Mechanical mitral valve replacement in infants and young children is associated with substantial morbidity and mortality. Lifelong anticoagulation is required, with all the accompanying challenges of maintaining levels in infants and children whose dietary input continually changes. Even with careful control of all aspects that can perturb the coagulation cascade, these patients have a substantial lifelong risk of thrombotic and hemorrhagic complications that can also affect the durability of the valve. Anticoagulation is usually achieved utilizing warfarin with the degree of anticoagulation measured via the international normalized ratio (INR). Unfortunately, in some cases, the INR can be falsely elevated and lead to inappropriate reassurance. We describe a 4-year-old patient with complex congenital heart disease palliated via a single ventricular pathway with a mechanical atrioventricular valve replacement. The patient experienced acute valvular thrombosis while receiving warfarin with INR at target levels. Chromogenic factor X (CFX) levels were discordant with INR measurements, suggesting a subtherapeutic level of anticoagulation despite maintaining the standard INR target. Therefore, CFX levels were used to interpret INR measurements and guide an individualized approach to anticoagulation. We propose a new role of CFX: to verify and guide warfarin anticoagulation in high-risk pediatric patients including those undergoing mechanical mitral valve replacement.

Juvenile myelomonocytic leukemia (JMML) is a rare but severe pediatric neoplasm with hematopoietic stem cell transplant as its only established curative option. The development of targeted therapeutics for JMML is being guided by an understanding of the pathobiology of this condition. Here, we review JMML with an emphasis on genetics in order to (i) demonstrate the relationship between JMML genotype and clinical phenotype and (ii) explore potential genetic targets of novel JMML therapies. DNA hypermethylation studies have demonstrated consistently that methylation is related to disease severity. Increasing understanding of methylation in JMML may open the door to novel therapies, such as DNA methyltransferase inhibitors. The PI3K/AKT/MTOR, JAK/STAT, and RAF/MEK/ERK pathways are being investigated as therapeutic targets for JMML. Future therapy for JMML will be driven by an increased understanding of pathobiology. Targeted therapeutic approaches hold potential for improving outcomes in patients with JMML.

Although inhibitors of the kinases CHK1, ATR, and WEE1 are undergoing clinical testing, it remains unclear how these three classes of agents kill susceptible cells and whether they utilize the same cytotoxic mechanism. Here we observed that CHK1 inhibition induces apoptosis in a subset of acute leukemia cell lines in vitro, including TP53-null acute myeloid leukemia (AML) and BCR/ABL–positive acute lymphoid leukemia (ALL), and inhibits leukemic colony formation in clinical AML samples ex vivo. In further studies, downregulation or inhibition of CHK1 triggered signaling in sensitive human acute leukemia cell lines that involved CDK2 activation followed by AP1-dependent TNF transactivation, TNFα production, and engagement of a TNFR1- and BID-dependent apoptotic pathway. AML lines that were intrinsically resistant to CHK1 inhibition exhibited high CHK1 expression and were sensitized by CHK1 downregulation. Signaling through this same CDK2–AP1–TNF cytotoxic pathway was also initiated by ATR or WEE1 inhibitors in vitro and during CHK1 inhibitor treatment of AML xenografts in vivo. Collectively, these observations not only identify new contributors to the antileukemic cell action of CHK1, ATR, and WEE1 inhibitors, but also delineate a previously undescribed pathway leading from aberrant CDK2 activation to death ligand–induced killing that can potentially be exploited for acute leukemia treatment. Significance: This study demonstrates that replication checkpoint inhibitors can kill AML cells through a pathway involving AP1-mediated TNF gene activation and subsequent TP53-independent, TNFα-induced apoptosis, which can potentially be exploited clinically.

New diagnostic criteria and severity grading for sinusoidal obstructive syndrome (SOS) among pediatric and adolescent young adult (AYA) patients have been recently endorsed by international consensus. The extent to which these have been adopted in the US remains unclear. We sought to assess the potential impact via retrospective application of these criteria among patients treated at a large academic center in the United States. This is a single center retrospective study of pediatric-AYA patients who underwent hematopoietic cell transplantation (HCT) between July 2009 and 2019. The incidence of SOS was assessed using historic Baltimore and Seattle diagnostic criteria and compared with more recent guidelines (pEBMT) as proposed by the Paediatric Diseases Working Party of the European Society for Blood and Marrow Transplantation. Among 226 patients, application of the pEBMT diagnostic criteria was associated with a higher incidence (15.9%) and earlier time to diagnosis of SOS (by 2.5-3 days) compared with the modified Seattle (12.3%), and Baltimore (6.6%) criteria, respectively. The pEBMT criteria were sensitive and highly specific. Refractory thrombocytopenia was present in 75% of patients at diagnosis. Approximately 61% of patients with SOS were anicteric at diagnosis, though the majority (94.4%) developed hyperbilirubinemia as SOS progressed over a median time of 4 (1-57) days. Application of pEBMT criteria may have resulted in earlier indication for definitive treatment by 3 days. Timely diagnosis and administration of definitive treatment of SOS has been associated with improved outcomes. Prospective studies may better characterize the risk factors and natural course of SOS using pEBMT criteria.

Germline predisposition syndromes (GPS) result from constitutional aberrations in tumor suppressive and homeostatic genes, increasing risk for neoplasia in affected kindred. In this study, we present clinical and genomic data on 144 Mayo Clinic patients with GPS; 59 evaluated prospectively using an algorithm-based diagnostic approach in the setting of a dedicated GPS/ inherited bone marrow failure syndrome (IBMFS) clinic. Seventy-two (50%) patients had IBMFS (telomere biology disorders-32,Fanconi anemia-18, Diamon Blackfan Anemia - 11, congenital neutropenia-5, Schwachman-Diamond Syndrome-5 and Bloom Syndrome-1), 27 (19%) had GPS with antecedent thrombocytopenia (RUNX1-FPD-15, ANKRD26-6, ETV6-2, GATA1-1, MPL-3), 28 (19%) had GPS without antecedent thrombocytopenia (GATA2 haploinsufficiency-16, DDX41-10, CBL-1 and CEBPA-1) and 17 (12%) had general cancer predisposition syndromes (ataxia telangiectasia-7, heterozygous ATM variants-3, CHEK2-2, TP53-2, CDK2NA-1, NF1-1 and Nijmegen Breakage Syndrome-1). Homozygous and heterozygous ATM pathogenic variants were exclusively associated with lymphoproliferative disorders (LPD), while DDX41 GPS was associated with LPD and myeloid neoplasms. The use of somatic NGS-testing identified clonal evolution in GPS patients, with ASXL1, RAS pathway genes, SRSF2 and TET2 being most frequently mutated. Fifty-two (91%) of 59 prospectively identified GPS patients had a change in their management approach, including additional GPS-related screening in 42 (71%), referral for allogenic HSCT workup and screening of related donors in 16 (27%), medication initiation and selection of specific conditioning regimens in 14 (24%), and genetic counseling with specific intent of fertility preservation and preconceptual counselling in 10 (17%) patients; highlighting the importance of dedicated GPS screening, detection and management programs for patients with hematological neoplasms. This article is protected by copyright. All rights reserved.

CPX-351 is a liposomally encapsulated 5:1 molar ratio of cytarabine and daunorubicin that recently received regulatory approval for the treatment of therapy-related acute myeloid leukemia (AML) or AML with myelodysplasia-related changes based on improved overall survival compared to standard cytarabine/daunorubicin therapy. Checkpoint kinase 1 (CHK1), which is activated by DNA damage and replication stress, diminishes sensitivity to cytarabine and anthracyclines as single agents, suggesting that CHK1 inhibitors might increase the effectiveness of CPX-351. The present studies show that CPX-351 activates CHK1 as well as the S and G2/M cell cycle checkpoints. Conversely, CHK1 inhibition diminishes the cell cycle effects of CPX-351. Moreover, CHK1 knockdown or addition of a CHK1 inhibitor such as MK-8776, rabusertib or prexasertib enhances CPX-351-induced apoptosis in multiple TP53-null and TP53-wildtype AML cell lines. Likewise, CHK1 inhibition increases the antiproliferative effect of CPX-351 on primary AML specimens ex vivo, offering the possibility that CPX-351 may be well suited to combine with CHK1-targeted agents.

Background Active surveillance for transfusion reactions is critically important among pediatric patients undergoing chemotherapy. Among pediatric-adolescent-young-adult (AYA) hematology/oncology patients, who have been typically excluded from transfusion reaction studies, this profile remains poorly characterized. Methods We assessed the incidence and clinical characteristics of transfusion reactions (n = 3246 transfusions) in this population (n = 201 patients) at our center. Findings The incidence of adjudicated transfusion reactions was 2·04%. The incidence was higher for platelet (2·78%) compared to packed red blood cell transfusions (1·49%) (p = 0·0149). The majority (61·4%) of all reactions were classified as febrile non-haemolytic transfusion, while 35·7% were considered allergic, and 2·9% were classified as transfusion-associated circulatory overload. The incidence of transfusion reactions in patients who were pre-medicated was higher (2·51%) than in patients who were not (1·52%) (p = 0·0406). Sub-set analysis revealed a 3·95% incidence of adjudicated transfusion reactions among recipients of immune effector cells (IECs) (n = 3), all of which occurred during the potential window for cytokine release syndrome; two-thirds of these reactions were severe/potentially life-threatening. Interpretation The incidence of transfusion reactions among pediatric-AYA hematology/oncology patients may be lower than the general pediatric population. Patients with a prior history of transfusion reactions and those receiving platelet transfusions may be at higher risk for reaction. From our limited sample, IEC recipients may be at risk for severe transfusion reactions. Large multi-center prospective studies are needed to characterize transfusion reactions in this population. Appropriate characterization of reactions in this population may inform risk stratification and mitigate missed opportunities for prompt recognition and appropriate management. Funding None.

The εγδβ thalassemias (EGDBT) are infrequently occurring deletions of the β globin gene cluster on chromosome 11. EGDBTs can be an unsuspected cause of severe neonatal anemia that resolves during the first year of life into a normal Hb A2 thalassemic phenotype, presumed to be due to an imbalance of β-like chains during development. First described in 1972, they are categorized into two groups, both with loss of the five DNase I hypersensitivity sites upstream of the β gene (HBB) called the locus control region (LCR). In group 1 deletions, all or most of the β globin gene cluster including HBB is deleted; in group 2 deletions, removal of the LCR silences an intact HBB. Large deletions that do not involve LCR but remove the embryonic (HBE) and fetal genes (HBG2/HBG1) [LCR(ε Gγ Aγ) 0δβ] have not been reported. It is not known whether a deletion with intact LCR as well as δ and β genes would similarly manifest as neonatal anemia that resolves into a normocytic phenotype with normal hemoglobin fraction percentages after infancy. Four individuals with an LCR(ε Gγ Aγ) 0δβ deletion have been evaluated. These include monochorionic, diamniotic twin girls whose newborn screen (NBS) returned significant for Hb A percentage greater than Hb F for both twins. NBS was repeated two weeks later with the same result. The newborns were induced late pre-term (36 weeks and 6 days) after an uncomplicated pregnancy, including no features of twin to twin transfusion. Both infants had no anemia and bilirubin levels remained in the low to low-intermediate risk zones. Neither twin received transfusions or phototherapy during admission. At a follow up visit at 20 months of age a hemoglobin electrophoresis was performed which showed borderline Hb A2 and no Hb F in both twins (Table 1). Ferritin levels were low-normal in Twin A (14 µg/L) and low in Twin B (9 µg/L). Both infants were found to have a heterozygous large deletion affecting HBE, HBG2, HBG1, and HBBP1 loci by Multiplex Ligation-dependent Probe Amplification (MLPA), a method that uses multiple DNA probe pairs to determine the size of the DNA segment deleted. MLPA deletion/duplication testing on the α genes was negative. No β globin variants were identified by DNA sequencing. An evaluation was performed on the 25 year-old healthy mother and showed similar findings including the heterozygous large deletion. Mother and infants continue to be asymptomatic with normal red cell indices for age (Table 1). The fourth was an unrelated 40-year-old female with mild anemia screened by hemoglobin electrophoresis for obstetric evaluation who was found to have borderline Hb A2 (see table 1). MLPA showed a heterozygous deletion involving the same loci. Again, no β globin variants were identified by DNA sequencing. All four cases showed the same MLPA pattern except one non-specific probe commonly altered in common gamma gene conversion events. Long range sequencing performed on one case confirmed a single contiguous 32,599 bp deletion that matched the MLPA data (g.5262276-5294875). The detected deletion has not been reported in literature and differs from EGDBT mutations in that the LCR is intact. As the LCR controls expression of the entire gene cluster, this mutation is expected to display different phenotypic features than classic EGDBT. HBD and HBB are not deleted and therefore adequate transcription of Hb A2 and Hb A are expected with no imbalance of α/β chains after the neonatal period. It is postulated this finding explains the decreased Hb F levels in the NBS test result. The Hb A2 increase is likely a product of this deletion and does not indicate β-thalassemia. The heterozygous absence of HBE and HBG2/HBG1 may result in upregulation of HBD and HBB expression through loss of FKLF and FKLF-2 binding. In addition, HBB-EKLF binding would have less competition as the gamma promoter elements have been heterozygously deleted. In summary, in contrast to classic EGDBTs which cause transient severe neonatal anemia and resolve to normal Hb A2 thalassemic indices, this novel LCR(ε Gγ Aγ) 0δβ deletion was associated with normal CBC values with an absence of severe neonatal anemia, inverted Hb F/Hb A percentages at birth and borderline Hb A2 levels. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Context: Germline predisposition syndromes (GPS) are genetic disorders that increase the risk of all types of malignancies, with a growing list of genes associated specifically with hematological malignancies. Although many of these conditions have syndromic features, some GPS patients present without identifiable traits. We have established a hematology GPS clinic that uses an algorithmic approach to diagnose GPS patients. Objective: To illustrate the heterogeneity of GPS and the benefits of an algorithmic approach to identify non-syndromic GPS patients. Design: Medical records were reviewed retrospectively from patients diagnosed with GPS at our institution from 1994 to 2018. Prospectively, we investigated new pediatric and adult patients with GPS from 2017 to 2020 using an algorithmic approach summarized as follows: 1) Evaluation of relevant family history, 2) phenotype-specific functional assays (telomere measurement, breakage assay, erythrocyte adenosine deaminase testing), 3) germline genetic testing through a custom-designed gene panel, and 4) research whole exome sequencing for negative cases. Both a detailed explanation of the algorithm and the methodology for genetic variant interrogation are included in Mangaonkar et al. MC Proc 2019. Setting: This study was carried out at the Division of Hematology at Mayo Clinic. Patients or Other Participants: GPS was investigated in pediatric and adult patients with one or more first-degree relatives with hematological/visceral malignancies, in those with antecedent thrombocytopenia, or in those with specific features indicative of inherited bone marrow failure (IBMF) (short telomere syndromes, GATA2 haploinsufficiency, Fanconi anemia, Schwachman-Diamond syndrome). Interventions: N/A Main Outcomes Measures: The number of patients diagnosed with GPS both retrospectively and prospectively were tallied and compared. Results: A total of 146 individuals were included in the study divided as follows: 28 (19.4%) presented with hematological malignancy with precedent thrombocytopenia, 27 (18.8%) without precedent thrombocytopenia, 74 (51.3%) showed IBMF, and 15 (10.4%) showed general cancer predisposition syndrome. Eighty-five patients were retrospectively included, while 61 were prospectively evaluated through our algorithmic approach. Among retrospective patients, 7.1% (6 patients) did not present syndromic features, while this value increased to 14.7% (9 patients) when using the algorithmic approach. Conclusions: By using an algorithmic approach, we can identify a higher percentage of GPS patients without syndromic features.

Hereditary thrombotic thrombocytopenic purpura is an ultra-rare disorder caused by biallelic mutations in the ADAMTS13 gene. Because it can be difficult to diagnose, plasma ADAMTS13 activity assessment should be considered in patients with thrombocytopenia, anemia, and schistocytes on peripheral blood smear. We present the diagnostic evaluation of a patient with hereditary thrombotic thrombocytopenic purpura. Genetic testing revealed one known pathogenic mutation and one novel mutation of ADAMTS13 classified as likely pathogenic on the basis of parental genetic testing and in silico analyses. We further discuss off-label use of prophylactic plasma-derived Factor VIII (Koate-DVI) and the benefit of rare disease registries.

Autologous hematopoietic cell transplant is performed in selected pediatric solid tumors to allow for administration of high-dose chemotherapy. In cases of tandem transplants, there is also a reduced period of recovery in between transplant cycles. There is no concern for rejection or graft-versus-host disease as patients are getting their own hematopoietic cells, and the recovery of peripheral counts is more rapid because of use of peripheral blood hematopoietic cells. High-dose chemotherapy with autologous hematopoietic cell rescue is generally more efficacious in tumors that have demonstrated chemosensitivity and have minimal residual disease before transplant. The two most common solid tumors that have demonstrated efficacy with high-dose chemotherapy followed by autologous hematopoietic cell rescue are neuroblastoma stage IV and high-risk medulloblastoma. This regimen is also used for other embryonal central nervous system tumors and as salvage therapy for recurrent germ cell tumors. Its role in high-risk, metastatic, and relapsed Ewing's sarcoma is debatable. Autologous transplant has been used in several other pediatric solid tumors such as high-grade gliomas, osteosarcoma, soft tissue sarcomas, and Wilms tumor without as much success. In this chapter, we will present the current recommendations for transplant in pediatric solid tumors.

Background Patients undergoing chemotherapy and especially hematopoietic stem cell transplantation (HSCT) require frequent transfusions, and thus, transfusion reaction (TR) vigilance is critical in this population. The reported incidence of TRs across all patients is 2%, and pediatric patients may experience 2-2.6 times more reactions than adults. However, the TR profile may differ in the immunocompromised population. There is a paucity of data in this area, as pediatric oncology and HSCT patients are often excluded from TR studies. Our goals were to assess the prevalence and describe TRs among immunocompromised pediatric patients and to improve recognition of TRs across this population. Methods Pediatric clinical providers completed a TR training module in May – June, 2019. A single-institution retrospective review was conducted. All TRs in patients aged less than 25 years were reviewed over a 3-month period from July 1, 2019 to October 1, 2019. Results Over a 3-month period, 1,786 transfusions were administered in our designated population. Of those, 50.4% were platelets, 44.0% were red blood cells (RBC), 3.4% were cryoprecipitate, 1.4% were thawed plasma, and 0.8% were granulocytes. Those undergoing HSCT consumed 27.7% of total transfusions. Of all transfusions, there were 48 (2.7%) reported as possible TRs by nursing. Of those, 30 (1.7% of all transfusions) were adjudicated as true TRs. Fourteen (46.7%) of these true TRs were in patients with leukemia, 9 (30.0%) with HSCT, 5 (16.7%) with solid tumors, and 2 (6.7%) with aplastic anemia. Of the 9 reactions in HSCT patients, 4 occurred in allogeneic transplant recipients (3 umbilical cord blood and one matched unrelated donor) and 5 were in those receiving autologous HSCT. In HSCT patients, 1.8% of transfusions resulted in TRs compared to 1.6% in non-HSCT patients. Of the products triggering reactions, platelets accounted for 22 TRs (73.3%) and RBCs accounted for 8 TRs (26.7%). Of all 30 TRs, 15 (50%) were classified as febrile non-hemolytic transfusion reactions (FNHTR), 14 (46.7%) were considered allergic reactions, and 1 (3.3%) was diagnosed as transfusion-associated circulatory overload. Pre-medication was given in 22 (76.7%) of transfusions causing reactions. Of the 18 reports that were not adjudicated as true TRs, most (n=15) were generated for fever, but deemed unrelated to transfusion. Conclusions Our baseline analysis revealed a higher prevalence than our historical institutional prevalence (1.7% vs. 1.3%), consistent with higher rates of TRs in the pediatric population, but lower than the 2% quoted in the literature, suggesting either underreporting or a different TR phenotype in this population. This population had a higher prevalence of FNHTR than the general pediatric population (50.0% vs. 31.5%). High rates of pre-medication and comorbidities (resulting in fevers) may influence TR presentation in this population.

Though membranous nephropathy is a much more common cause of nephrotic syndrome in the adult population, it accounts for only a small fraction of cases in pediatrics. We report a case of a 16-year-old boy with nephrotic syndrome due to membranous nephropathy in the setting of a rare tumor, angiomatoid fibrous histiocytoma. This patient’s nephrotic-range proteinuria completely resolved following resection of this tumor. Angiomatoid fibrous histiocytoma, while known to cause other paraneoplastic syndromes such as anemia, has never been reported to cause membranous nephropathy. This case highlights a novel and treatable secondary cause of membranous nephropathy. Because secondary causes are more common in children than in adults, a high index of suspicion for other underlying pathology including malignancy should be considered. It also suggests that urinalysis may be a helpful screening tool in cases of angiomatoid fibrous histiocytoma.

Background: Sinusoidal obstructive syndrome (SOS) is a potentially catastrophic complication of stem cell transplantation (SCT) which disproportionately affects younger patients. The incidence of SOS may vary widely depending on the diagnostic criteria (Baltimore versus Seattle), and delays in initiation of definitive treatment remains the most important predictor of outcome. Recently proposed pediatric diagnostic and severity grading criteria by the European Society of Blood and Marrow Transplantation (EBMT) may offer increased sensitivity and allow for more prompt diagnosis, but the extent to which these have been adopted and/or validated by centers in the United States is unclear. Methods: This is a retrospective analysis of all patients undergoing SCT on the Pediatric service at MD Anderson Cancer Center from 2009-2019. Patient records were reviewed for diagnosis of SOS. Among patients identified with SOS, application of Baltimore, Seattle and pediatric EBMT (pEBMT) criteria were compared. Descriptive statistics were used for data analysis where appropriate. Results: A total of 248 patients received 268 transplants during the study period. Patient characteristics are summarized in Table 1. When Baltimore criteria was used the incidence of SOS was 4.5% (n=12) as compared to 8.2% (n=22) when the Seattle or pEBMT criteria were applied. At diagnosis, the majority of these patients had moderate to very severe disease according to pEBMT criteria. The median time to diagnosis of SOS varied according to diagnostic criteria used, with a trend to earlier diagnosis with pEBMT criteria (13 days post-SCT with pEBMT versus 15 days with Seattle/Baltimore) as shown in Table II. Prior exposure to inotuzumab and gemtuzumab were associated with high rates of SOS (75% and 86% respectively). Anicteric SOS, refractory thrombocytopenia and rising bilirubin from a baseline value on 3 consecutive days or bilirubin ≥2 mg/dL within 72 hours were present in 63.6%, 77.3% and 91% of patients with SOS, when pEBMT criteria were applied. Late-onset SOS (diagnosed after 21 days post-SCT) was present in 22.7% of patients when Seattle or pEBMT criteria were applied (n=5) and could not be diagnosed per Baltimore criteria. Severe SOS was eventually observed in 95% of patients. Severe ascites requiring paracentesis (23%), impaired coagulation (77%), respiratory distress requiring supplemental oxygen and/or invasive pulmonary ventilation ( 55%), delirium (32%), acute kidney injury/KDIGO Stage 3/requiring renal replacement therapy (50%) were observed. Defibrotide treatment was initiated in 55% of patients with a median duration of treatment of 26 (3-74) days and complete resolution of SOS was observed in 42% of these patients. For patients who were initiated on defibrotide on the day of diagnosis (n=7) versus those who were not (range 1-11 days) the median time to complete resolution of SOS was 35 and 20 days respectively (p=0.2). Conclusions: To our knowledge, this is the first reported retrospective analysis of SOS among pediatric and adolescent young adult SCT patients in the United States using pEBMT SOS diagnostic and severity criteria. Our study was limited by small sample size associated with single center analyses. Use of the pEBMT criteria showed a trend to earlier time to diagnosis by a median of two days. This is a potentially clinically significant finding, as a delay in initiation of defibrotide among children with severe SOS, has been associated with statistically significant decreased rates of complete resolution. Inherent flaws of the Baltimore and Seattle criteria are the time restriction and reliance of hyperbilirubinemia for the diagnosis in children and adolescents and young adults. Our retrospective analysis suggests that pEBMT criteria for the diagnosis of SOS among children and young adults may be appropriate, especially given the rates of anicteric and late-onset SOS seen in this population. Disclosures Petropoulos: Foundation for the Accreditation of Cellular Therapy (FACT): Membership on an entity's Board of Directors or advisory committees, Other: Foundation for the Accreditation of Cellular Therapy (FACT). Kebriaei:Amgen: Research Funding; Jazz: Consultancy; Pfizer: Honoraria; Kite: Honoraria. Wierda:Xencor: Research Funding; Janssen: Research Funding; Loxo Oncology Inc.: Research Funding; KITE pharma: Research Funding; Juno Therapeutics: Research Funding; Gilead Sciences: Research Funding; Acerta Pharma Inc: Research Funding; Pharmacyclics LLC: Research Funding; Genentech: Research Funding; GSK/Novartis: Research Funding; AbbVie: Research Funding; Cyclcel: Research Funding; Oncternal Therapeutics Inc.: Research Funding; Miragen: Research Funding; Sunesis: Research Funding. Mahadeo:Recipient of unrestricted medical education grant from Jazz: Research Funding; PI for ATARA EBV CTL Trials: Other: Other .

Acute appendicitis in children with acute leukemia is uncommon and often recognized late. Immunocompromised host state coupled with the importance of avoiding treatment delays makes management additionally challenging. Leukemic infiltration of the appendix though rare must also be considered. Although successful conservative management has been reported, surgical intervention is required in most cases. We present our experience with acute appendicitis in children with acute leukemia and a case of complete remission of acute myeloid leukemia with a short course of decitabine. Decitabine may serve as bridging therapy in critically ill patients who are unable to undergo intensive chemotherapy., Highlights • Acute appendicitis in children with acute leukemia is uncommon and often recognized late. • AML requires intensive chemotherapy which further compromises the clinical state of the patient. • Immunocompromised state and intestinal wall leukemic involvement makes treatment challenging. • We present a case of remission of AML with a short course of decitabine, a hypomethylating agent. • Decitabine may serve as bridging therapy and help achieve disease control in critically ill patients.

Introduction: Topoisomerase I is a nuclear enzyme that relaxes torsional strain in DNA by nicking one DNA strand, allowing rotation, then resealing the DNA backbone. This is an important enzyme in replication and transcription, and therefore has been targeted by anti-cancer agents such as camptothecins. These agents intercalate into DNA at the topoisomerase I active site and inhibit the religation step catalyzed by the enzyme, causing increased topoisomerase I-DNA complexes that impede advancing replication forks or transcription complexes, leading to DNA damage and cell death. Platinating agents also stabilize topoisomerase I-DNA covalent complexes. The topotecan/carboplatin combination has recently shown promise in combination with the PARP inhibitor veliparib in aggressive and transformed myeloproliferative neoplasms (MPNs) and chronic myelomonocytic leukemia (K Pratz et al., Clin Cancer Res. 23:899, 2017). Given that both classes of agents have a narrow therapeutic window, it is important to try to predict the sensitivity/resistance of these agents in malignancies such as acute myeloid leukemia (AML) and transformed MPNs. Some of mechanisms of drug resistance that have been described are decreased numbers of drug-stabilized topoisomerase I-DNA complexes due to drug efflux, diminished topoisomerase I expression or topoisomerase I mutation. Thus, being able to detect and quantify these DNA-protein complexes may provide insight into drug sensitivity. Methods: Using a unique monoclonal antibody that detects topoisomerase I-DNA covalent complexes (A. Patel et al., Nucleic Acids Res. 44:2816, 2016), immunofluorescence techniques were used to quantify these topoisomerase I-DNA complexes in AML cell lines (SET2, HEL, K562, U937, ML2, MV-4-11, THP1, HL60, ML1, and Molm13) and clinical AML samples. To verify the fidelity of the anti-topoisomerase I-DNA covalent complex antibody (TopIcc), siRNA knockdown methods were utilized with confirmatory immunofluorescence and Western blotting. Slot blots were additionally used to assess the presence of these complexes in AML cell lines. Western blots were performed to assess topoisomerase I levels in AML cell lines. Topotecan drug sensitivity analysis was performed by using an MTS assay. Results: With treatment of the topoisomerase I inhibitor, topotecan, there was an increase in the percentage of leukemia cells positive for the topoisomerase I-DNA covalent complexes. The degree of increase in complexes varied across cell lines and patient samples. To ensure we were detecting TopIcc by immunofluorescence, we performed a topoisomerase-I siRNA knockdown to confirm the specificity of the antibody for TopIcc's. Slot blots on multiple AML cell lines confirmed the presence of topoisomerase-DNA covalent complexes. The Western blot of all the AML cell lines, ordered from low to high TopIcc revealed increasing amounts of topoisomerase I. The MTS assay revealed lower topotecan IC50 values in three of the cell lines with higher complex formation, including Molm13, ML1 and ML2 (IC50 6-8 nM compared to 13-46 nM in the other cell lines). Conclusions: Based on recent clinical results, there has been renewed interested in topoisomerase I inhibitors, especially for aggressive and transformed MPNs. Topoisomerase I-DNA complex repair/downregulation has been a hallmark of drug resistance to topoisomerase I inhibitors. Therefore, detecting and quantifying these complexes in treated samples has been hypothesized to provide insight into the drug sensitivity, which is particularly important in camptothecins and platinating agents given their narrow therapeutic windows. Immunodetection techniques using an anti-TopIcc antibody may help predict sensitivity of AML to topoisomerase I inhibitors and will be used as a correlative biomarker study in an upcoming phase II randomized study of topotecan/carboplatin with or without veliparib or placebo in advanced myeloproliferative disorders and chronic myelomonocytic leukemia (ClinicalTrials.gov NCT03289910). Disclosures Pratz: AbbVie: Consultancy, Research Funding; Agios: Research Funding; Astellas: Consultancy, Research Funding; Boston Scientific: Consultancy; Millenium/Takeda: Research Funding. Kaufmann:Mayo Clinic: Patents & Royalties: Co-inventor on a patent held by Mayo Clinic for the use of the anti-TOP1cc antibody as a diagnostic reagent.

Rates of venous thromboembolism have increased in the adolescent population over the last two decades, likely due to advanced diagnostics, increased use of central venous catheters, chronic medical conditions, obesity, and oral contraceptive use [1]. Of these factors, a modifiable risk factor for adolescents is obesity. Sedentary lifestyle and prolonged immobilization are additional prothrombotic risk factors that are often associated with obesity. With ever-increasing screen time, sedentary behavior has risen accordingly, especially among gamers. We present four cases of adolescents who developed life-threatening venous thromboembolic events in the setting of obesity, sedentary lifestyle and/or immobilization, and prolonged video game use.

HCC is rare in the pediatric population, but is the second most common liver malignancy in children. Survival rates for primary unresectable HCC have been dismal. The objective of this study was to describe our experience with a multimodal approach for the management of unresectable HCC in two adolescent patients and to review the literature. Both patients are currently alive with no recurrence at 51 and 29 months post-transplant. Multimodality treatment involving chemotherapy with doxorubicin, cisplatin, and sorafenib; TACE; timely liver transplantation; and post-transplant therapy with sorafenib and mTOR inhibitors may help improve outcomes and prolong survival in pediatric patients with unresectable HCC.