Statistical analysis
The survival rate was estimated using the Kaplan–Meier method. An event was defined as progression of disease, toxic death, or secondary cancer. In addition, prognostic factors were assessed using univariate and multivariate Cox proportional hazard regression models. Prognostic factors assessed using univariate analysis were age, INSS stage, bone metastasis, bone marrow metastasis, liver metastasis, MSI15, MYCN amplification, INPC pathology, INRC before HDC, radiation, surgery before HDC, retinoic acid, and tandem SCT. Factors showing significant adverse effects on event-free survival (EFS) in a log-rank test were assessed using a multivariable model. All statistical analyses were performed using the R package version 3.3.3.