Abstract: We identified three RCTs including 739 children. They all used an age of one year as the cut-off point for pre-treatment risk stratification. The first updated search identified a manuscript reporting additional follow-up data for one of these RCTs, while the second update identified an erratum of this study. There was a significant statistical difference in event-free survival in favour of myeloablative therapy over conventional chemotherapy or no further treatment (three studies, 739 patients; HR 0.78, 95% CI 0.67 to 0.90). There was a significant statistical difference in overall survival in favour of myeloablative therapy over conventional chemotherapy or no further treatment (two studies, 360 patients; HR 0.74, 95% CI 0.57 to 0.98). However, when additional follow-up data were included in the analyses the difference in event-free survival remained statistically significant (three studies, 739 patients; HR 0.79, 95% CI 0.70 to 0.90), but the difference in overall survival was no longer statistically significant (two studies, 360 patients; HR 0.86, 95% CI 0.73 to 1.01). The meta-analysis of secondary malignant disease and treatment-related death did not show any significant statistical differences between the treatment groups. Data from one study (379 patients) showed a significantly higher incidence of renal effects, interstitial pneumonitis and veno-occlusive disease in the myeloablative group compared to conventional chemotherapy, whereas for serious infections and sepsis no significant difference between the treatment groups was identified. No information on quality of life was reported. In the individual studies we evaluated different subgroups, but the results were not univocal in all studies. All studies had some methodological limitations. Based on the currently available evidence, myeloablative therapy seems to work in terms of event-free survival. For overall survival there is currently no evidence of effect when additional follow-up data are included. No definitive conclusions can be made regarding adverse effects and quality of life, although possible higher levels of adverse effects should be kept in mind. A definitive conclusion regarding the effect of myeloablative therapy in different subgroups is not possible. This systematic review only allows a conclusion on the concept of myeloablative therapy; no conclusions can be made regarding the best treatment strategy. Future trials on the use of myeloablative therapy for high-risk neuroblastoma should focus on identifying the most optimal induction and/or myeloablative regimen. The best study design to answer these questions is a RCT. These RCTs should be performed in homogeneous study populations (e.g. stage of disease and patient age) and have a long-term follow-up. Different risk groups, using the most recent definitions, should be taken into account. It should be kept in mind that recently the age cut-off for high risk disease was changed from one year to 18 months. As a result it is possible that patients with what is now classified as intermediate-risk disease have been included in the high-risk groups. Consequently the relevance of the results of these studies to the current practice can be questioned. Survival rates may be overestimated due to the inclusion of patients with intermediate-risk disease.

Plain-language summary: This systematic review focused on randomised studies comparing the effectiveness of myeloablative therapy with conventional therapy in children with high-risk neuroblastoma. The authors found three studies including 739 patients. These studies provide evidence that myeloablative therapy improves event-free survival (that is, the time until a certain event, for example tumour progression, the development of a second tumour, or death from any cause occurs). For overall survival (that is, the time until a patient dies from any cause, so not only from the tumour or its treatment, but for example, also from a car accident) there is no evidence of a better outcome in patients treated with myeloablative therapy. Side effects such as renal (kidney) effects, interstitial pneumonitis (a type of lung disease) and veno-occlusive disease (a condition in which some of the small veins in the liver are obstructed) were more common in patients treated with myeloablative therapy than conventional chemotherapy. It should be noted that this systematic review only allows a conclusion on the concept of myeloablative therapy; no conclusions regarding the best treatment strategy with regard to, for example, types of chemotherapeutic agents and the use of radiation therapy, could be made. More high quality research is needed. It should be noted that recently the age cut-off for high-risk disease was changed from one year to 18 months. As a result it is possible that patients with what is now classified as intermediate-risk disease were included in the high-risk groups. Consequently the relevance of the results of these studies to the current practice can be questioned. Survival rates may be overestimated due to the inclusion of patients with intermediate-risk disease.