General principles of neoplasia are applicable to CNS tumors

1.The neoplastic cell must have a growth advantage within the microenvironment. Therefore, tumor cells tend to phenotypically resemble cells normally present within the CNS.
2.The chance of transformational events depends on the number of replicating cells "at risk"
3.Once transformation is established, mutational events leading to increased growth advantage correlate with decreased cellular differentiation and more aggressive behavior.
4.Morbidity and mortality is related to invasion and metastasis. Here CNS tumors differ significantly from systemic cancer in that invasion with compression and/or destruction of normal structures is critical, while metastases are unusual, and largely irrelevant to the outcome in these patients.