Medulloblastoma, the most common pediatric malignant brain tumor, is comprised of a heterogeneous group of tumors with distinct molecular subtypes and clinical outcomes. In particular, tumors with a cancer stem cell (CSC) population have been observed to be more resistant to conventional therapies, necessitating the elucidation of pathways important in this population. Work in our lab has shown that neurosphere culture-enriched cells from Ptch1LacZ/+;Trp53-/- mouse medulloblastomas exhibit properties of self-renewal, expression of neural stem cell (NSC) markers and potent tumor-initiation. The pathway dependencies and mechanisms of self-renewal in these medulloblastoma neurospheres (MBNS) have not yet been characterized.