Similarly, we observed that although all tumours initially formed spheres in high-density cell cultures, ‘spheres’ derived from low-grade astrocytomas, ependymomas and a beta-catenin activated medulloblastoma (associated with good prognosis35) could not be serially passaged, and initial sphere formation likely reflected fusion rather than sphere-forming ability. The gene discussed is CTNNB1; the disease is medulloblastoma.