Fig. 2. Models of oncogenic transformation.

(A) Experimental and clinical evidence indicates that granule cells are susceptible to oncogenic transformation into medulloblastomas as proliferating progenitors (solid line) and, possibly, early post-mitotic progenitors (dotted line), but the potential for tumorigenesis declines when they become mature neurons. (B) By contrast, for astrocytomas the period of susceptibility for oncogenesis might extend to mature forms of astrocytes within the CNS.