PTCH1 and medulloblastoma: Our findings might be of relevance for medulloblastoma, as one subgroup of medulloblastoma with constitutive activation of the SHH/PTCH pathway has been shown to originate from granule cerebellar progenitors in the external granule layer (EGL), for which immortalized CB cells might be used as a model system for medulloblastoma [24,25].