MYCN and neoplasm: In line with the in vitro results, a neuroblastoma PDX model harboring a DDX1-MYCN coamplification was significantly more sensitive to rapamycin than a model only harboring an MYCN amplification, as evidenced by decreased tumor growth and increased histologic signs of cell death, as measured by IHC detection of caspase-3 cleavage (Fig. 6F–J; Supplementary Fig. S9H).