For the majority of the hepatoblastoma tumoroids (6 of 9 tested), colony formation was abolished in the absence of the standard growth factors usually included in the media (EGF, FGF10, and HGF) (Fig. 6a, e) or in the presence of a MEK inhibitor, U0126 (Fig. 6b, Supplementary Fig. S9a). The gene discussed is MAP2K7; the disease is hepatoblastoma.