Metastatic disease can be viewed as two simultaneously occurring diseases. Brain cancer  and systemic cancer (elsewhere in the body). Each disease has quite different  mortality rates. Untreated brain metastases are rapidly fatal, while systemic cancer may not be.

Metastatic brain disease is a focal disease and focal control of the tumor is paramount to patient survival. The approach in the past has been to treat metastatic brain disease as a whole brain disease, with whole brain radiation (WBR). Because of poor local control of tumor growth when treated solely by WBR, brain metastases in the past were rapidly lethal. Therefore patients with brain metastases did not benefit from many advances in cancer therapy (immuno therapy, chemo therapy, conformal radiotherapy etc.) because these therapies do no effectively reach brain metastases and individuals died quickly from neurological progression.

Now neurological progression can be effectively controlled in most patients harboring a few intracranial metastases with aggressive focal treatment (surgery or radiosurgery) in combination with WBR.  WBR can be given immediately following focal treatment or at the time of recurrence. Control can be extended by frequent MR surveillance of the brain and  radiosurgical treatment of new metastases months or years later. With control of intracranial disease, advances in cancer therapy will prolong survival, since most patients now succumb later to systemic, rather than intracranial disease. Aggressive, focal treatment is only beneficial in patients with controlled or no systemic disease and independent health (Karnofsky Performance Score (KPS)> 70). Age is also a determinant of outcome, with better outcomes in individuals less than 60 years old.