Demographics of brain metastasis.

Brain metastases are the most common intracranial tumor, significantly out-numbering primary brain tumors. The apparent increase in the ratio of brain metastases to primary tumors may be the result of a number of factors, including the possibility of a CNS "pharmacologic sanctuary," an aging population, and improved imaging studies. Among adults, the most common origins of brain metastasis include primary tumors of the lung, breast, skin (melanoma), and gastrointestinal tract. Among patients under 21 years of age, brain metastases most often arise from the sarcomas and germ cell tumors.