The study protocol was prospectively registered in PROSPERO (CRD42020146491) [27]. We followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines.
Search Strategy
We systematically searched PubMed and EMBASE for relevant articles and abstracts published between 1 January, 2015 and 27 February, 2020, using strategies that included keywords and suggested MeSH and Emtree entry terms, their synonyms, and closely related words (Table 1 of the Electronic Supplementary Material [ESM]). Searches were not limited by language. Our search strategies were checked using the Canadian Agency for Drugs and Technologies in Health peer-review checklist for search strategies [28].
We performed a complementary search of ClinicalTrials.gov on 23 June, 2020 to find pediatric oncology studies with posted results (LZ, MTW). Then, all studies with registration numbers were searched by two researchers independently (KS, MTW) for additional publications on ClinicalTrials.gov and/or Google Scholar on 3 July, 2020. For a detailed description of the search methodology, see the ESM.
Study Selection and Eligibility Criteria
Five researchers (LZ, MTW, KS, ES, MB) performed title and abstract screening for initial study inclusion and four researchers (LZ, MTW, ES, JS) performed full-text screening to determine the final list of included studies. The study selection process was conducted independently by two researchers, any disagreements were resolved by discussion, and when necessary an arbiter was involved (MW, BG).
We included pediatric cancer phase II clinical trials that published their results in the last 5 years as well as phase I/II or phase II/III studies (if phase II results were reported separately) investigating targeted therapy agents. Key inclusion criteria were as follows: (1) all or a majority of participants (over 50%) were under 21 years old and/or the study was indicated as pediatric, or results were provided separately for the pediatric population; (2) diagnosis of any malignancy (solid or hematological); and (3) assessment of toxicity and/or response of targeted therapy or a combination of targeted therapies (monoclonal antibodies or small molecules or antibody drug conjugates [29]). We excluded studies evaluating: (1) chemotherapy and immunotherapy regimens, or a combination of these with targeted therapy; (2) topical only or regionally administered drugs (i.e., delivered directly to the tumor without any systemic effects); (3) non-pharmacological modalities (e.g., surgery, radiotherapy, gene therapy, stem cell therapy, or any of these combined with targeted therapy); or (4) supportive care without anticancer agents or with other interventions not falling under a targeted therapy category (e.g., antiviral agents). Inclusion and exclusion criteria were defined prospectively in the protocol [27].
Data Extraction
We created and piloted a data extraction form. On the basis of the pilot, we refined and prepared the final version (available from https://osf.io/m7fw3/). Data were extracted from each publication and/or ClinicalTrials.gov study record independently by two reviewers (LZ, MTW, ES, JS). All reviewers received training prior to extraction. Disagreements were resolved by discussion, and when necessary, a third person, an arbiter, was involved (MW). An experienced medical oncologist had a supervisory role (BG). In the case of multiple publications for the same study, the results from the full publication and/or the most recent version were used in the extraction.
From each study, we extracted data related to: study characteristics (e.g., year of results publication, phase, funding, study status), patient characteristics (e.g., age, number of enrolled and eligible participants, type of malignancy), intervention (e.g., number and names of investigated drugs), and outcomes (e.g., toxicity, response). For more details, see our extraction form (https://osf.io/m7fw3/).
Data Curation
Phase II studies do not generally measure survival endpoints; thus, we decided to use the objective response rate as a proxy for the therapeutic benefit [30]. For solid tumor studies, we defined benefit as the proportion of participants with partial and/or complete response (reported separately or as an objective response rate) as defined by study authors. To measure benefit for hematological malignancy studies (except for acute leukemias and chronic myeloid leukemia), we considered any of the various methods of measuring partial and/or complete response (e.g., cytogenetic, hematologic, or molecular). For acute leukemias and chronic myeloid leukemia, we did not count any types of partial responses in our assessment of benefit because anything short of a complete response is not considered a benefit for these malignancies [31, 32].
We defined risk as the proportion of participants experiencing grade 3, 4, or 5 drug-related AEs as defined by the Common Toxicity Criteria for Adverse Events, Version 5.0 (and earlier versions) [33]. An AE was considered as related to the study drug if it was clearly stated by the study authors; expressions such as “AEs at least possibly related to study therapy”, “treatment-emergent AEs”, and “AEs suspected to be drug related” were also acceptable. In cases where a fatal event was not clearly described as treatment related, we excluded it from our drug-related grade 5 AE rate estimations. All data on AEs in our analysis are treatment related. To compare the risks and benefits, we analyzed a cohort of studies where both drug-related deaths (grade 5 AEs) and responses were clearly reported.
Statistical Analysis
Pooled response rate, treatment-related fatal (grade 5) AE rate, and treatment-related grade 3/4 AEs rate were calculated within each stratum when more than one study provided data using meta-analytic methods. Modeling with random effects and the restricted maximum likelihood estimator were used to account for between-study heterogeneity. I2 statistics were calculated to provide a measure of the proportion of overall variation attributable to between-study heterogeneity. Differences in response rates between the categories of study definition, number of drugs, and the number of types of malignancies were assessed using the Q test for heterogeneity in meta-regression. Pooled response was calculated for categories of publication year (2015–16, 2017–18, and 2019–20) to assess changes over time. P-values for trends in response between 2015 and 2020 were obtained from a meta-regression. A meta-analysis was conducted using the metafor package (R, Version 3.2.3); p < 0.05 was considered statistically significant. All tests were two-sided. The average number of treatment-related grade 3 and 4 AEs per person with a 95% confidence interval (CI) was estimated using a Poisson regression model.
Analysis of Both Solid Tumor and Hematological Malignancy Studies
Because large differences were observed in responses between solid tumors and hematological malignancies, we stratified our analyses by the type of cancer. For three studies that included both solid and hematological malignancies, patients were separated for response data and, for one study including both these cancer types, we separated data on the drug-related fatal (grade 5) AE rate. The data separation did not influence response rates or drug-related fatal (grade 5) AEs rates in our analysis.
Risk of Bias Assessment
Two authors (LZ, MTW) independently assessed the risk of bias for all included studies using the Cochrane risk of bias tools for randomized or non-randomized studies [34, 35]. Judgments were based on the algorithms proposed by the authors of ROBINS and RoB2 tools, adjusted to fit the specific aspects of our analysis. Disagreements were resolved by discussion.