Metastatic brain tumor involves a mass of cancerous cells in the brain that have spread from another part of the body.

Metastatic (secondary) brain tumor occurs when there is a tumor in an area of the body, most commonly the lungs or the breast, and cells from that tumor break off, travel in the bloodstream (metastasize), and lodge in the brain. Other tumors that commonly spread to the brain include melanoma, kidney cancer, and germ cell tumors (such as testicular or ovarian cancers).

Tumors may be localized to a small area, invasive (spread to nearby areas), benign (noncancerous) or malignant (cancerous). They can directly destroy brain cells, or they may indirectly damage cells by producing inflammation, compressing other parts of the brain as the tumor grows, inducing cerebral edema (brain swelling), and causing increased intracranial pressure (the pressure within the skull).

Classification of metastatic brain tumors depends on the exact site of the tumor within the brain, type of tissue involved, original location of the tumor, and other factors.

Metastatic brain tumors occur in about one-fourth of all cancers that metastasize (spread through the body). They are much more common than primary brain tumors. They occur in approximately 10-30% of adult cancers.