Moreover, we provide evidence that IGF-I overexpression in cerebellum cooperates with deregulation of the Shh pathway to further enhance brain overgrowth in double mutants, and to accelerate medulloblastoma development by significantly increasing the incidence of early, as well as full medulloblastoma stages in Ptc1+/-/IGF-I Tg compared with Ptc1+/- mice. This evidence concerns the gene SHH and medulloblastoma.