Mayo Clinic indicates primary brain tumors are caused by normal cells that mutate to form a mass of abnormal cells in the brain. Secondary brain tumors are more common, and these types of tumors form after cancer from another part of the body spreads to the brain.
Primary brain tumors spread more quickly than normal cells, and the mass increases even though healthy cells are killed. Mayo Clinic explains that primary brain tumors are named by the types of cells involved with the malignancy. These varieties include acoustic neuromas, meningiomas, ependymomas, pineoblastomas, germ cell tumors, gliomas and medulloblastomas. Meningiomas, as their name implies, begin in the membranes that cover the brain known as meninges.
Secondary brain tumors start as cancer in other parts of the body. These tumors are most likely to occur in patients with a history of cancer, according to Mayo Clinic. The most common types of cancer that metastasize to the brain include breast, colon, kidney, skin and lung cancers. Any type of cancer may spread to the brain if left untreated.
WebMD states that a few risk factors exist for brain tumors. Children who receive radiation to the head are more likely to develop tumors as adults. People with rare genetic disorders and patients over age 65 also have higher risks for brain tumors. As of Nov. 2014, around 35,000 new cases of primary brain tumors and 23,380 new cases of brain cancer are diagnosed each year.