PTCH1 and neoplasm: In this report, however, we observe that no significant change in tumor frequency of Ptch1+/− mice occurs after deletion of Btg1. This is quite surprising given the increase of proliferation of cerebellar GCPs caused by the ablation of Btg1 in Patched1 wild-type background; moreover, Btg1 has been shown to act as oncosuppressor in MB cells which strongly inhibits the proliferation (12) and also in several types of tumors (14, 29).