Updated October 12, 2014.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

The most common causes of brain tumors in adults actually don't arise in the brain.   Often, tumors in the brain have spread (metastasized) from another location.  Brain metastases occur in 10 to 30 percent of adults with cancer.

Brain metastases usually portend a poor outcome.  The average survival of people with brain metastases and who do not receive treatment with surgery, chemotherapy or radiation is about one or two months.

In adults, the malignancies most likely to spread to the brain are lung, breast, kidney, colorectal, and melanoma.  In children, the most likely are sarcomas, neuroblastoma and germ cell tumors.   The overall incidence of brain metastases in people with cancer seems to be increasing, likely due to longer survival times in people with cancer and due to improved ability to find metastases with neuroimaging techniques.

Metastases usually reach the brain via the bloodstream, and so they are most commonly found in areas where blood vessels are narrowest.  Tiny vessels can act as a filter where metastatic tumor cells can cluster.  The most common brain location is at the junction of grey and white matter near the edges of the brain. 

Brain metastases cause different symptoms depending on their location.  Headaches occur in about 40 to 50 percent.  This headache is typically worse on one side and may be associated with nausea and vomiting about 40 percent of the time.  Bending over, coughing, or sneezing may worsen the headache due to increased intracranial pressure.

  Hemiparesis or other focal neurological deficits are the first sign of a brain metastasis in about 20 to 40 percent of patients, and cognitive dysfunction is the first sign in about 30 percent.  Seizures are the first sign in about 10 to 20 percent.  Melanoma, choriocarcinoma, thyroid and renal carcinomas can cause bleeding in the brain. 

Metastases may be distinguished from primary brain lesions by their particular localization near the edge of the brain, well circumscribed margins, and the presence of multiple lesions.  Biopsy remains the gold standard. 

cFor some reason, gastrointestinal and breast cancers are more likely to spread to the back of the brain, whereas small cell lung cancer distributes more evenly.  Breast, colon and renal cell carcinoma are more likely to cause single metastases, whereas lung cancer and melanoma tend to cause multiple metastases.

The treatment of brain metastases depends on the overall prognosis of the patient. Factors used to determine this include the patient’s level of neurological functioning, age less than 65, and not having metastases outside the brain. Even under these good conditions, the median survival time is about 7 months. 

In patients with favorable prognoses, the goal is eradication of the metastases.  This can include surgical resection and/or radiation therapy.  Surgical resection or tumor lesioning with single high dose stereotactic radiosurgery is best undertaken if there are only 1 to 3 visible metastases.  While surgery can rapidly relieve symptoms, complications are not uncommon;  13 percent of patients in one series suffered some major complication as a result of these procedures.

If there are more metastases, whole brain radiation therapy (WBRT) is usually preferred, especially as it is assumed that there are further metastases invisible to the imaging scan.  Radiation of the entire brain in conjunction with surgery has been demonstrated in randomized trials to be more efficacious than either treatment alone.  However, whole brain radiation therapy can worsen cerebral edema, and so it is recommended that steroids be given beforehand. 

In those with a poor prognosis, the goal is to control symptoms related to the metastases. Surgical resection or stereotactic radiosurgery is usually not performed.  While whole brain radiation therapy is still done, but with a goal of attempting to prevent further deterioration of brain function.  The response rate of WBRT alone is about 40 to 60 percent. 

Whatever the patient’s prognosis, seizures can be treated with anti-epileptics, and vasogenic edema can be managed with corticosteroids.  Tumors may predispose towards the formation of blood clots, and this may also need to be treated.  In addition, treatment of the primary tumor is simultaneously performed, and the presence of brain metastases may impact the selection of chemotherapeutic agent used.    

While the prognosis for people with brain metastases is generally poor, sometimes people do improve.  Regardless, steps can be taken to improve the quality of that person’s life.

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Mehta MP, Rodrigus P, Terhaard CH, et al. Survival and neurologic outcomes in a randomized trial of motexafin gadolinium and whole-brain radiation therapy in brain metastases. J Clin Oncol 2003; 21:2529.

Posner JB. Management of brain metastases. Rev Neurol (Paris) 1992; 148:477.     

Sawaya R, Hammoud M, Schoppa D, et al. Neurosurgical outcomes in a modern series of 400 craniotomies for treatment of parenchymal tumors. Neurosurgery 1998; 42:1044.</sub>