MYCN and bone metastasis: In the training cohort, univariate analysis showed that age above 18 months, non-mediastinal tumor, UFH, INSS stage 3–4, bone marrow metastasis, bone metastasis, NMYC amplification, high-risk group, and high D-dimer group were unfavorable factors for OS (all P < 0.05) (Table 2).