Activation of the ERK/MAPK pathway: a signature genetic defect in posterior fossa pilocytic astrocytomas. - Forshew T; Tatevossian RG; Lawson AR; Ma J; Neale G; Ogunkolade BW; Jones TA; Aarum J; Dalton J; Bailey S; Chaplin T; Carter RL; et al. (The Journal of pathology, 2009)