DDX1 and neoplasm: MYCN-MB fusion transcripts were unique to each tumor; 2 recurrent fusion-partner genes, DDX1 and NBAS (immediately upstream of MYCN41) were involved in fusions with each other and additional partners (MYCNOS) in 3 MYCN-MBGrp3/4 tumors, but fusion position and gene order were not conserved (Supplementary Figure 4B).