TropicALL study: Thromboprophylaxis in Children treated for Acute Lymphoblastic Leukemia with Low-molecular-weight heparin: a multicenter randomized controlled trial

A systematic review and meta-analysis of the effectiveness of primary thromboprophylaxis in acute lymphoblastic leukemia during early-phase therapy including asparaginase or its prolonged form

Asparaginase is essential in the initial management of acute lymphoblastic leukemia (ALL) but frequently leads to venous thromboembolism (VTE). Using anticoagulants for primary VTE prevention has been studied with no consensus. We conducted a systematic literature search in PubMed, Scopus, and Web of science and performed random-effect meta-analysis using Mantel-Haenszel method in RevMan 5.4 to analyze primary pharmacological thromboprophylaxis during asparaginase treatment in early-phase (induction, consolidation, or intensification phase) therapy in patients with ALL with all ages and followed with subgroup analysis by age. Meta-analysis of 13 articles describing the effect of antithrombin supplementation in 1375 patients showed that antithrombin prophylaxis decreases the risk of VTE by 43% (RR, 0.57; 95% CI, 0.38 - 0.83; p=0.004), with mild heterogeneity (I2=35%, p=0.10) and moderate certainty by GRADE. 8 articles included for meta-analysis of low-molecular weight heparin (LMWH) treatment in 612 patients showed that it decreased the risk of VTE by nearly 40% (RR, 0.61; 95% CI, 0.45 - 0.81; p=0.00081), with minimal heterogeneity (I2=14%, p=0.31) but low certainty. Subgroup analysis showed that only prophylaxis with antithrombin supplementation significantly decreased the VTE rate in adult patients with moderate certainty. In pediatric patients, one nonrandomized prospective study showed that LMWH combined with antithrombin has a better thromboprophylaxis effect than antithrombin alone. In the PREVAPIX-ALL trial, prophylaxis with direct factor Xa inhibitor Apixaban did not benefit children younger than 18 years except for cases of obesity. We concluded that thromboprophylaxis with antithrombin is effective in ALL patients older than 18 years during the early phase of therapy, and LMWH combined with antithrombin supplementation might be effective for pediatric patients with ALL. Apixaban is effective in pediatric ALL patients with obesity and needs further study in other high-risk patients.

A Review of Acute Lymphocytic Leukemia (ALL) in the Pediatric Population: Evaluating Current Trends and Changes in Guidelines in the Past Decade

Acute lymphocytic leukemia (ALL) is a commonly diagnosed cancer in children. Despite technological advancements to improve treatment and survival rates, there has been a steady increase in the incidence of ALL and treatment failures. This paper discusses the pathogenic interaction between genetic and environmental factors leading to childhood ALL. It evaluates the current treatment guidelines and notable obstacles leading to resistance, relapse, and treatment toxicities. The review evaluates a 10-year trend in the management guidelines of pediatric ALL through a systematic literature review of records from 2012 to 2023. Findings show that improvement in the five-year survival rates, notwithstanding rates of relapse and incurable diseases, is still high. Furthermore, several risk factors, including an interplay between genetic and environmental factors, are largely contributory to the outcome of ALL treatments and its overall incidence. Moreover, huge financial costs have remained a significant challenge in outcomes. There remains a need to provide individualized treatment plans, shared decision-making, and goals of care as parts of the management guidelines for the best possible outcomes. We expect that future advancements will increase overall survival rates and disease-free years.

Pediatric cancer-associated thrombosis: Analysis from a tertiary care cancer center in India

BACKGROUND AND AIMS

Thrombotic events (TEs) have been extensively studied in adult cancer patients, but data in children are limited. We prospectively analyzed pediatric cancer-associated thrombosis (PCAT) in children with malignancies.

METHODS

Children below 15 years of age with confirmed malignancies, treated at a large tertiary cancer center in India from July 2015 to March 2020 developing any TE were eligible. A standardized approach for detection and management was followed. Data were collected after informed consent.

RESULTS

Of 6132 eligible children, 150 (2.44%) had 152 TEs, with median age 8.5 years and male:female of 1.83:1. Most TEs occurred on chemotherapy: 111 (74.0%). The most common site was central nervous system (CNS) 59 (39.3%), followed by upper-limb venous system 37 (24.7%). Hemato-lymphoid (HL) malignancies were more prone to PCAT than solid tumors (ST) (incidence 3.23% vs. 1.58%; odds ratio [OR] = 2.06, 95% confidence interval [CI] [1.36-2.88]; p < .001). Malignancies associated with PCAT were acute lymphoblastic leukemia (ALL) 2.94%, acute myeloid leukemia (AML) 6.66%, and non-Hodgkin lymphomas 5.35%. Response imaging done in 106 (70.7%) children showed complete to partial resolution in almost 90% children. Death was attributable to TE in seven (4.66%) children. Age above 10 years (OR 2.33, 95% CI [1.59-3.41]; p < .001), AML (OR 4.62, 95% CI [1.98-10.74]; p = .0062), and non-Hodgkin lymphoma (OR 4.01, 95% CI [1.15-14.04]; p = .029) were significantly associated with TEs. In ALL, age more than 10 years (OR 1.86, 95% CI [1.06-3.24]; p < .03), T-ALL (OR 3.32, 95% CI [1.69-6.54]; p = .001), and intermediate-risk group (OR 4.97, 95% CI [1.12-22.02]; p = .035) were significantly associated with thrombosis. The 2-year event-free survival (EFS) for HL malignancies with PCAT was 55.3% versus 72.1% in those without PCAT (p = .05), overall survival (OS) being 84.6% versus 80.0% (p = .32).

CONCLUSION

Incidence of PCAT was 2.4%, and occurred predominantly in older children with hematolymphoid malignancies early in treatment. Most resolved completely with low molecular weight heparin (LMWH) and mortality was low. In hematolymphoid malignancies, PCAT reduce EFS, highlighting the need for prevention.

Current Use of Asparaginase in Acute Lymphoblastic Leukemia/Lymphoblastic Lymphoma

Pediatric Acute Lymphoblastic Leukemia (ALL) cure rates have improved exponentially over the past five decades with now over 90% of children achieving long-term survival. A direct contributor to this remarkable feat is the development and expanded understanding of combination chemotherapy. Asparaginase is the most recent addition to the ALL chemotherapy backbone and has now become a hallmark of therapy. It is generally accepted that the therapeutic effects of asparaginase is due to depletion of the essential amino acid asparagine, thus occupying a unique space within the therapeutic landscape of ALL. Pharmacokinetic and pharmacodynamic profiling have allowed a detailed and accessible insight into the biochemical effects of asparaginase resulting in regular clinical use of therapeutic drug monitoring (TDM). Asparaginase's derivation from bacteria, and in some cases conjugation with a polyethylene glycol (PEG) moiety, have contributed to a unique toxicity profile with hypersensitivity reactions being the most salient. Hypersensitivity, along with several other toxicities, has limited the use of asparaginase in some populations of ALL patients. Both TDM and toxicities have contributed to the variety of approaches to the incorporation of asparaginase into the treatment of ALL. Regardless of the approach to asparagine depletion, it has continually demonstrated to be among the most important components of ALL therapy. Despite regular use over the past 50 years, and its incorporation into the standard of care treatment for ALL, there remains much yet to be discovered and ample room for improvement within the utilization of asparaginase therapy.

Challenges in Management of VTE in Children With Cancer: Risk Factors and Treatment Options

Venous thromboembolism (VTE) occurs in 2.1 to up to 50% of children with cancer and contributes to long term morbidity as well as early mortality in this population. Pediatric patients with malignancy are predisposed to VTE due to the prothrombotic nature of cancer and its associated coagulopathies as well as chemotherapeutic agents, use of central venous catheters, surgery, radiotherapy, and concomitant thrombophilia. Management of thrombosis in this population is challenging due to concomitant thrombocytopenia, associated bleeding risks, concurrent co-morbidities, and toxicities of therapy. The aim of this paper is to highlight clinically relevant issues and management dilemmas using clinical vignettes. We review the clinical significance of asymptomatic and symptomatic thrombosis, examine the various options for asparaginase-associated thrombosis, address the role and controversies of direct oral anticoagulants, and describe our approach to managing anticoagulation therapy in the context of chemotherapy-induced thrombocytopenia.

Supportive methods for childhood acute lymphoblastic leukemia then and now: A compilation for clinical practice

Survival of childhood acute lymphoblastic leukemia has significantly improved over the past decades. In the early years of chemotherapeutic development, improvement in survival rates could be attained only by increasing the cytostatic dose, also by modulation of the frequency and combination of chemotherapeutic agents associated with severe short- and long-time side-effects and toxicity in a developing child's organism. Years later, new treatment options have yielded promising results through targeted immune and molecular drugs, especially in relapsed and refractory leukemia, and are continuously added to conventional therapy or even replace first-line treatment. Compared to conventional strategies, these new therapies have different side-effects, requiring special supportive measures. Supportive treatment includes the prevention of serious acute and sometimes life-threatening events as well as managing therapy-related long-term side-effects and preemptive treatment of complications and is thus mandatory for successful oncological therapy. Inadequate supportive therapy is still one of the main causes of treatment failure, mortality, poor quality of life, and unsatisfactory long-term outcome in children with acute lymphoblastic leukemia. But nowadays it is a challenge to find a way through the flood of supportive recommendations and guidelines that are available in the literature. Furthermore, the development of new therapies for childhood leukemia has changed the range of supportive methods and must be observed in addition to conventional recommendations. This review aims to provide a clear and recent compilation of the most important supportive methods in the field of childhood leukemia, based on conventional regimes as well as the most promising new therapeutic approaches to date.

Prophylactic anticoagulation in children receiving home parenteral nutrition

BACKGROUND

Children with intestinal failure (IF) are at risk of loss of vascular access because of catheter-related venous thrombosis. Whether primary prophylactic anticoagulation is effective and safe in preventing catheter-related thrombosis is largely unknown. Our aim was to assess the incidences of catheter-related venous thrombosis and bleeding complications in children with IF receiving home parenteral nutrition (HPN) treated with primary prophylactic anticoagulation.

METHODS

All children, aged 0-18 years, treated with HPN at the Emma Children's Hospital/Amsterdam UMC were followed from January 2007 to July 2019. All patients were offered primary prophylactic anticoagulation from the start of HPN. The primary outcomes were catheter-related venous thrombosis and bleeding on prophylactic anticoagulation.

RESULTS

In total, 55 (76%) of 74 patients received primary prophylactic anticoagulation. The median age at the start of prophylaxis was 8.4 (interquartile range [IQR], 5.0-55.7) months. Patients were followed for a median of 31.2 (IQR, 10.7-53.5) months, with a total of 65,463 catheter days. The incidence of catheter-related thrombosis on prophylactic anticoagulation was 0.2 per 1000 catheter days. In total, the incidence of clinically relevant bleeding was 0.1 per 1000 catheter days. The median time to first event was 1268 (IQR, 149-2014) days for thrombosis and 389 (IQR, 227-2912) days for clinically relevant bleeding. Cumulative event-free survival after 5 years was 78% for thrombosis.

CONCLUSIONS

Our study shows a low rate of catheter-related venous thrombosis and a slightly elevated rate of clinically relevant bleeding in children receiving HPN and primary prophylactic anticoagulation.

How we approach thrombosis risk in children with COVID-19 infection and MIS-C

Thrombosis within the microvasculature and medium to large vessels is a serious and common complication among critically ill individuals with coronavirus disease 2019 (COVID-19). While children are markedly less likely to develop severe disease than adults, they remain at risk for thrombosis during acute infection and with the post-acute inflammatory illness termed multisystem inflammatory syndrome in children. Significant knowledge deficits in understanding COVID-19-associated coagulopathy and thrombotic risk pose clinical challenges for pediatric providers who must incorporate expert opinion and personal experience to manage individual patients. We discuss clinical scenarios to provide framework for characterizing thrombosis risk and thromboprophylaxis in children with COVID-19.

Risk factors for the development of hospital-acquired pediatric venous thromboembolism-Dealing with potentially causal and confounding risk factors using a directed acyclic graph (DAG) analysis

Introduction

Hospital-acquired venous thromboembolism (HA-VTE) in children comprises multiple risk factors that should not be evaluated separately due to collinearity and multiple cause and effect relationships. This is one of the first case-control study of pediatric HA-VTE risk factors using a Directed Acyclic Graph (DAG) analysis.

Material and methods

Retrospective, case-control study with 22 cases of objectively confirmed HA-VTE and 76 controls matched by age, sex, unit of admission, and period of hospitalization. Descriptive statistics were used to define distributions of continuous variables, frequencies, and proportions of categorical variables, comparing cases and controls. Due to many potential risk factors of HA-VTE, a directed acyclic graph (DAG) model was created to identify confounding, reduce bias, and increase precision on the analysis. The final model consisted of a DAG-informed conditional logistic regression.

Results

In the initial conventional univariable model, the following variables were selected as potential risk factors for HA-VTE: length of stay (LOS, days), immobility, ICU admission in the last 30 days, LOS in ICU, infection, central venous catheter (CVC), number of CVCs placed, L-asparaginase, heart failure, liver failure, and nephrotic syndrome. The final model using the set of variables selected by DAG analysis revealed LOS (OR = 1.106, 95%CI = 1.021–1.198, p = 0.013), L-asparaginase (OR = 26.463, 95%CI = 1.609–435.342, p = 0.022), and nephrotic syndrome (OR = 29.127, 95%CI = 1.044–812.508, p = 0.004) as independent risk factors for HA-VTE.

Conclusion

The DAG-based approach was useful to clarify the influence of confounders and multiple causalities of HA-VTE. Interestingly, CVC placement—a known thrombotic risk factor highlighted in several studies—was considered a confounder, while LOS, L-asparaginase use and nephrotic syndrome were confirmed as risk factors to HA-VTE. Large confidence intervals are related to the sample size; however, the results were significant.

Impact of exogenous antithrombin on low molecular weight heparin anti-Xa activity assays in a pediatric and young adult leukemia and lymphoma cohort with variable antithrombin levels

BACKGROUND

Low molecular weight heparin (LMWH) remains the most commonly prescribed pediatric anticoagulant. There is debate whether LMWH anti-Xa assays with or without exogenous antithrombin (AT) best reflect anticoagulation effect, and how much discrepancy exists between assay types.

OBJECTIVES

We assessed the effect of variable AT activity on LMWH anti-Xa levels in plasma samples from anticoagulated pediatric and young adult acute lymphoblastic leukemia and lymphoma (ALL/L) patients, using two instruments and their commercial kits with and without exogenous AT (ie, four platforms).

METHODS

We analyzed LMWH anti-Xa levels on 60 plasma samples with known AT activity from 12 enoxaparin-treated ALL/L patients, using four commercial kits from Siemens and Stago containing AT or not, on Siemens BCS and Stago STA R Max, respectively.

RESULTS

Of 236/240 samples with interpretable results, mean AT activity was 80% (46-138%). Correlation was acceptable for published kit ranges of LMWH anti-Xa levels when comparing kits containing AT (r = 0.82, P < .0001), or not (r = 0.93, P < .0001), and within a manufacturer (Berichrom to Innovance, r = 0.92, P < .0001; Stachrom to STA-Liquid Anti-Xa r = 0.98, P < .0001). LMWH anti-Xa levels were lower in platforms without added AT (P < .0001). For Stago kits, this effect increased when AT < 70% (P = .001, n = 19, mean 56%). Assay variability, measured as mean percent difference, was less pronounced with Stago kits (14.7%, n = 49) than Siemens (41.9%, n = 50).

CONCLUSIONS

Although LMWH levels from anti-Xa assays with added AT trend higher than in those without, correlation was fairly good between platforms in pediatric ALL/L plasmas, even when AT activity was <70%.

Prophylaxis of thromboembolism during therapy with asparaginase in adults with acute lymphoblastic leukaemia

BACKGROUND

The risk of venous thromboembolism is increased in adults and enhanced by asparaginase-based chemotherapy, and venous thromboembolism introduces a secondary risk of treatment delay and premature discontinuation of key anti-leukaemic agents, potentially compromising survival. Yet, the trade-off between benefits and harms of primary thromboprophylaxis in adults with acute lymphoblastic leukaemia (ALL) treated according to asparaginase-based regimens is uncertain.  OBJECTIVES: The primary objectives were to assess the benefits and harms of primary thromboprophylaxis for first-time symptomatic venous thromboembolism in adults with ALL receiving asparaginase-based therapy compared with placebo or no thromboprophylaxis. The secondary objectives were to compare the benefits and harms of different groups of primary systemic thromboprophylaxis by stratifying the main results per type of drug (heparins, vitamin K antagonists, synthetic pentasaccharides, parenteral direct thrombin inhibitors, direct oral anticoagulants, and blood-derived products for antithrombin substitution).

SEARCH METHODS

We conducted a comprehensive literature search on 02 June 2020, with no language restrictions, including (1) electronic searches of Pubmed/MEDLINE; Embase/Ovid; Scopus/Elsevier; Web of Science Core Collection/Clarivate Analytics; and Cochrane Central Register of Controlled Trials (CENTRAL) and (2) handsearches of (i) reference lists of identified studies and related reviews; (ii) clinical trials registries (ClinicalTrials.gov registry; the International Standard Randomized Controlled Trial Number (ISRCTN) registry; the World Health Organisation's International Clinical Trials Registry Platform (ICTRP); and pharmaceutical manufacturers of asparaginase including Servier, Takeda, Jazz Pharmaceuticals, Ohara Pharmaceuticals, and Kyowa Pharmaceuticals), and (iii) conference proceedings (from the annual meetings of the American Society of Hematology (ASH); the European Haematology Association (EHA); the American Society of Clinical Oncology (ASCO); and the International Society on Thrombosis and Haemostasis (ISTH)). We conducted all searches from 1970 (the time of introduction of asparaginase in ALL treatment). We contacted the authors of relevant studies to identify any unpublished material, missing data, or information regarding ongoing studies.

SELECTION CRITERIA

Randomised controlled trials (RCTs); including quasi-randomised, controlled clinical, cross-over, and cluster-randomised trial designs) comparing any parenteral/oral preemptive anticoagulant or mechanical intervention with placebo or no thromboprophylaxis, or comparing two different pre-emptive anticoagulant interventions in adults aged at least 18 years with ALL treated according to asparaginase-based chemotherapy regimens. For the description of harms, non-randomised observational studies with a control group were eligible for inclusion.  DATA COLLECTION AND ANALYSIS: Using a standardised data collection form, two review authors independently screened and selected studies, extracted data, assessed risk of bias for each outcome using standardised tools (RoB 2.0 tool for RCTs and ROBINS-I tool for non-randomised studies) and the certainty of evidence for each outcome using the GRADE approach. Primary outcomes included first-time symptomatic venous thromboembolism, all-cause mortality, and major bleeding. Secondary outcomes included asymptomatic venous thromboembolism, venous thromboembolism-related mortality, adverse events (i.e. clinically relevant non-major bleeding and heparin-induced thrombocytopenia for trials using heparins), and quality of life. Analyses were performed according to the guidelines of the Cochrane Handbook for Systematic Reviews of Interventions. For non-randomised studies, we evaluated all studies (including studies judged to be at critical risk of bias in at least one of the ROBINS-I domains) in a sensitivity analysis exploring confounding.  MAIN RESULTS: We identified 23 non-randomised studies that met the inclusion criteria of this review, of which 10 studies provided no outcome data for adults with ALL. We included the remaining 13 studies in the 'Risk of bias' assessment, in which we identified invalid control group definition in two studies and judged outcomes of nine studies to be at critical risk of bias in at least one of the ROBINS-I domains and outcomes of two studies at serious risk of bias. We did not assess the benefits of thromboprophylaxis, as no RCTs were included. In the main descriptive analysis of harms, we included two retrospective non-randomised studies with outcomes judged to be at serious risk of bias. One study evaluated antithrombin concentrates compared to no antithrombin concentrates. We are uncertain whether antithrombin concentrates have an effect on all-cause mortality (risk ratio (RR) 0.55, 95% confidence interval (CI) 0.26 to 1.19 (intention-to-treat analysis); one study, 40 participants; very low certainty of evidence). We are uncertain whether antithrombin concentrates have an effect on venous thromboembolism-related mortality (RR 0.10, 95% CI 0.01 to 1.94 (intention-to-treat analysis); one study, 40 participants; very low certainty of evidence). We do not know whether antithrombin concentrates have an effect on major bleeding, clinically relevant non-major bleeding, and quality of life in adults with ALL treated with asparaginase-based chemotherapy, as data were insufficient. The remaining study (224 participants) evaluated prophylaxis with low-molecular-weight heparin versus no prophylaxis. However, this study reported insufficient data regarding harms including all-cause mortality, major bleeding, venous thromboembolism-related mortality, clinically relevant non-major bleeding, heparin-induced thrombocytopenia, and quality of life. In the sensitivity analysis of harms, exploring the effect of confounding, we also included nine non-randomised studies with outcomes judged to be at critical risk of bias primarily due to uncontrolled confounding. Three studies (179 participants) evaluated the effect of antithrombin concentrates and six studies (1224 participants) evaluated the effect of prophylaxis with different types of heparins. When analysing all-cause mortality; venous thromboembolism-related mortality; and major bleeding (studies of heparin only) including all studies with extractable outcomes for each comparison (antithrombin and low-molecular-weight heparin), we observed small study sizes; few events; wide CIs crossing the line of no effect; and substantial heterogeneity by visual inspection of the forest plots. Although the observed heterogeneity could arise through the inclusion of a small number of studies with differences in participants; interventions; and outcome assessments, the likelihood that bias due to uncontrolled confounding was the cause of heterogeneity is inevitable. Subgroup analyses were not possible due to insufficient data.  AUTHORS' CONCLUSIONS: We do not know from the currently available evidence, if thromboprophylaxis used for adults with ALL treated according to asparaginase-based regimens is associated with clinically appreciable benefits and acceptable harms. The existing research on this question is solely of non-randomised design, seriously to critically confounded, and underpowered with substantial imprecision. Any estimates of effect based on the existing insufficient evidence is very uncertain and is likely to change with future research.

Cancer and Tumor-Associated Childhood Stroke: Results From the International Pediatric Stroke Study

BACKGROUND

The prevalence of cancer among children with stroke is unknown. This study sought to evaluate cancer- and tumor-associated childhood ischemic stroke in a multinational pediatric stroke registry.

METHODS

Children aged 29 days to less than 19 years with arterial ischemic stroke or cerebral sinovenous thrombosis enrolled in the International Pediatric Stroke Study between January 2003 and June 2019 were included. Data including stroke treatment and recurrence were compared between subjects with and without cancer using Wilcoxon rank sum and chi-square tests.

RESULTS

Cancer or tumor was present in 99 of 2968 children (3.3%) with arterial ischemic stroke and 64 of 596 children (10.7%) with cerebral sinovenous thrombosis. Among children in whom cancer type was identified, 42 of 88 arterial ischemic stroke cases (48%) had brain tumors and 35 (40%) had hematologic malignancies; 45 of 58 cerebral sinovenous thrombosis cases (78%) had hematologic malignancies and eight (14%) had brain tumors. Of 54 cancer-associated arterial ischemic stroke cases with a known cause, 34 (63%) were due to arteriopathy and nine (17%) were due to cardioembolism. Of 46 cancer-associated cerebral sinovenous thrombosis cases with a known cause, 41 (89%) were related to chemotherapy-induced or other prothrombotic states. Children with cancer were less likely than children without cancer to receive antithrombotic therapy for arterial ischemic stroke (58% vs 80%, P = 0.007) and anticoagulation for cerebral sinovenous thrombosis (71% vs 87%, P = 0.046). Recurrent arterial ischemic stroke (5% vs 2%, P = 0.04) and cerebral sinovenous thrombosis (5% vs 1%, P = 0.006) were more common among children with cancer.

CONCLUSIONS

Cancer is an important risk factor for incident and recurrent childhood stroke. Stroke prevention strategies for children with cancer are needed.

Incidence of venous thrombosis after peg-asparaginase in adolescent and young adults with acute lymphoblastic leukemia

AIM

There are limited data describing incidence of symptomatic venous thromboembolism (VTE) in adolescent and young adult (AYA) acute lymphoblastic leukemia (ALL) patients receiving peg-asparaginase.

MATERIALS & METHODS

Single-institution retrospective analysis of 44 AYA ALL patients treated with peg-asparaginase. Rates of VTE and proposed risk factors were assessed.

RESULTS

18 patients (41%) had a symptomatic VTE following peg-asparaginase. The cumulative incidence rate was 25% (95% CI: 13-38%) within 30 days of the initial dose. Personal history of thrombosis was statistically significantly associated with an increased risk of VTE with HR of 2.73 (95% CI: 1.40-5.33, p = 0.003) after adjusting for gender.

CONCLUSION

These data indicate a high rate of VTE in the AYA ALL population following treatment with peg-asparaginase.

Cancer-associated thrombosis in pediatric patients

Childhood malignancy and especially acute lymphoblastic leukemia are increasingly associated with thromboembolism. The etiology of pediatric cancer associated thrombosis is multifactorial and may reflect a tumor mass effect, tumor thrombi, alterations of the hemostatic system, treatment-related hazards (e.g. procoagulant changes induced by chemotherapy), presence of central venous lines and comorbidities (e.g. inherited thrombophilia). With over 80% cure rates of childhood cancer, strategies for prevention as well as for early diagnosis and optimal treatment of thromboembolism in children with malignancies are of major importance. While the use of therapeutic low molecular weight heparin prevails, prospective studies regarding guidelines for treatment or prevention are currently lacking. This review will address the epidemiology, etiology and risk factors for thrombosis, describe the presently available evidence associated with current therapy, and offer a glimpse into future treatment options.

Low molecular weight heparin for prevention of central venous catheter-related thrombosis in children

BACKGROUND

The prevalence of children diagnosed with thrombotic events has been increasing in the last decades. The most common thrombosis risk factor in neonates, infants and children is the placement of a central venous catheter (CVC). It is unknown if anticoagulation prophylaxis with low molecular weight heparin (LMWH) decreases CVC-related thrombosis in children. This is an update of the Cochrane Review published in 2014.

OBJECTIVES

To determine the effect of LMWH prophylaxis on the incidence of CVC-related thrombosis and major and minor bleeding complications in children. Further objectives were to determine the effect of LMWH on occlusion of CVCs, number of days of CVC patency, episodes of catheter-related bloodstream infection (CRBSI), other side effects of LMWH (allergic reactions, abnormal coagulation profile, heparin-induced thrombocytopaenia and osteoporosis) and mortality during therapy.

SEARCH METHODS

The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase and CINAHL databases and World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov trials registers to 7 May 2019. We undertook reference checking of identified trials to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-randomised trials comparing LMWH to no prophylaxis (placebo or no treatment), or low-dose unfractionated heparin (UFH) either as continuous infusion or flushes (low-dose UFH aims to ensure the patency of the central line but has no systemic anticoagulation activity), given to prevent CVC-related thrombotic events in children. We selected studies conducted in children aged 0 to 18 years.

DATA COLLECTION AND ANALYSIS

Two review authors independently identified eligible studies, which were assessed for study methodology including bias, and extracted unadjusted data where available. In the data analysis step, all outcomes were analysed as binary or dichotomous outcomes. The effects of interventions were summarised with risk ratios (RR) and their respective 95% confidence intervals (CI). We assessed the certainty of evidence for each outcome using the GRADE approach.

MAIN RESULTS

One additional study was included for this update bringing the total to two included studies (with 1135 participants). Both studies were open-label RCTs comparing LMWH with low-dose UFH to prevent CVC-related thrombosis in children. We identified no studies comparing LMWH with placebo or no treatment. Meta-analysis found insufficient evidence of an effect of LMWH prophylaxis in reducing the incidence of CVC-related thrombosis in children with CVC, compared to low-dose UFH (RR 0.68, 95% CI 0.27 to 1.75; 2 studies; 787 participants; low-certainty evidence). One study (158 participants) reported symptomatic and asymptomatic CVC-related thrombosis separately and detected no evidence of a difference between LMWH and low-dose UFH (RR 1.03, 95% CI 0.21 to 4.93; low-certainty evidence; RR 1.17, 95% CI 0.45 to 3.08; low-certainty evidence; for symptomatic and asymptomatic participants respectively). There was insufficient evidence to determine whether LMWH impacts the risk of major bleeding (RR 0.27, 95% CI 0.05 to 1.67; 2 studies; 813 participants; low-certainty evidence); or minor bleeding. One study reported minor bleeding in 53.3% of participants in the LMWH arm and in 44.7% of participants in the low-dose UFH arm (RR 1.20, 95% CI 0.91 to 1.58; 1 study; 158 participants; very low-certainty evidence), and the other study reported no minor bleeding in either group (RR: not estimable). Mortality during the study period was reported in one study, where two deaths occurred during the study period. Both were unrelated to thrombotic events and occurred in the low-dose UFH arm. The second study did not report mortality during therapy per arm but showed similar 5-year overall survival (low-certainty evidence). No additional adverse effects were reported. Other pre-specified outcomes (including CVC occlusion, patency and CRBSI) were not reported.

AUTHORS' CONCLUSIONS

Pooling data from two RCTs did not provide evidence to support the use of prophylactic LWMH for preventing CVC-related thrombosis in children (low-certainty evidence). Evidence was also insufficient to confirm or exclude a difference in the incidence of major and minor bleeding complications in the LMWH prophylaxis group compared to low-dose UFH (low and very low certainty respectively). No evidence of a clear difference in overall mortality was seen. Studies did not report on the outcomes catheter occlusion, days of catheter patency, episodes of CRBSI and other side effects of LMWH (allergic reactions, abnormal coagulation profile, heparin-induced thrombocytopaenia and osteoporosis). The certainty of the evidence was downgraded due to risk of bias of the included studies, imprecision and inconsistency, preventing conclusions in regards to the efficacy of LMWH prophylaxis to prevent CVC-related thrombosis in children.

Thrombosis in pediatric patients with leukemia

Acute lymphoblastic leukemia (ALL) is the most common type of cancer diagnosed in children. It is reportedly the most common malignancy associated with thromboembolism in the pediatric age group. Over the last 2 decades, venous thromboembolism (VTE) has been increasingly diagnosed among pediatric ALL patients with an estimated incidence ranging from about 5% (for symptomatic cases) to about 30-70% (following sequential imaging studies in asymptomatic children). The etiology is multifactorial and may stem from alterations of the hemostatic system following various chemotherapy protocols (including use of l-Asparaginase), the presence of central venous lines (CVL), as well as comorbidities, e.g. inherited thrombophilia risk factors. Most symptomatic thrombotic events occur in the upper venous system or in the central nervous system (CNS). Prospective studies on the establishment of guidelines for treatment or prevention are lacking. The following review will address the epidemiology, etiology and risk factors for thrombosis, describe the currently available evidence, and address issues associated with diagnosis and treatment.

Obesity and risk for venous thromboembolism from contemporary therapy for pediatric acute lymphoblastic leukemia

INTRODUCTION

Acute lymphoblastic leukemia (ALL) therapy confers risk for venous thromboembolism (VTE) and associated acute and long-term morbidity. Obesity increases VTE risk in the general population but its impact on ALL therapy-associated VTE is unknown.

METHODS

In a retrospective cohort of children treated for ALL between 2008 and 2016 (n = 294), we analyzed obesity at diagnosis (body mass index [BMI] ≥95%) and subsequent development of VTE. A subset participated in two concurrent prospective ALL trials studying body composition via dual-energy X-ray absorptiometry (DXA) (n = 35) and hypercoagulability via thromboelastography (TEG) (n = 46). Secondary analyses explored whether precise measurement of body fat and/or global hemostasis ex vivo by TEG could further delineate VTE risk in the obese.

RESULTS

Overall, we found 27/294 (9.2%) patients developed symptomatic VTE during therapy, 19/27 (70%) occurred during Induction. Study-defined "serious" VTE developed in 4/294 (1.4%) of patients. Obesity but not overweight was strongly predictive of symptomatic VTE (obesity odds ratio = 3.8, 95% confidence interval 1.5-9.6, p = 0.008). In the DXA subset, only 2/35 patients developed symptomatic VTE. However, within those prospectively screened during Induction, 30% (14/46) developed VTE; eight (17%) of these were asymptomatic and found only via screening.

CONCLUSIONS

In this pediatric ALL cohort, obesity conferred more than a three-fold increased risk for symptomatic VTE. In a subgroup of patients who underwent active screening, up to a third were noted to have VTE (symptomatic and asymptomatic). TEG did not predict VTE. Additional studies are necessary to validate these findings and to further refine a risk-stratified approach to thrombo-prevention during ALL therapy.