BCOR and undifferentiated (embryonal) sarcoma: Prognostically informative variants included amplification of the MDM2 gene (P2766), associated with a poor prognosis in neuroblastoma [11], and a disease-defining BCOR-CCNB3 fusion (patient P3153), which helped explain an unexpectedly long survival and relapse-free progression of a child originally diagnosed with an undifferentiated sarcoma carrying a poor prognosis [12].