The Primary site is the location of the original cancer. Lung, breast, melanoma (skin cancer), colon and kidney cancers commonly spread to the brain. A metastatic brain tumor is usually found when a cancer patient begins to experience neurological symptoms and a brain scan (CT or MRI) is ordered.

Cancer cells, visible under a microscope, separate from the primary tumor and enter the circulatory (blood) system. The immune system attempts to destroy these migrating blood-borne cancer cells. However, if the number of cancer cells becomes very high, the immune system may become overwhelmed or tolerant of these cells.

Metastatic tumors are diagnosed using a combination of neurological examination and imaging techniques. A physician may use more than one type of scan to make a diagnosis. MRI or CT are the most commonly available – the use of contrast dye makes the tumor(s) easier to see.

Although scans provide the physician with a “probable” diagnosis, examination of a sample of tumor tissue under a microscope confirms the exact pathologic diagnosis. The tissue sample may be obtained during surgery to remove the tumor or during a biopsy. A biopsy is a surgical procedure to remove a small amount of tumor for diagnosis.