Causes

Brain tumors that begin in the brain

Primary brain tumors originate in the brain itself or in tissues close to it, such as in the brain-covering membranes (meninges), cranial nerves, pituitary gland or pineal gland.

Primary brain tumors begin when normal cells acquire errors (mutations) in their DNA. These mutations allow cells to grow and divide at increased rates and to continue living when healthy cells would die. The result is a mass of abnormal cells, which forms a tumor.

Primary brain tumors are much less common than are secondary brain tumors, in which cancer begins elsewhere and spreads to the brain.

Many different types of primary brain tumors exist. Each gets its name from the type of cells involved. Examples include:

• Gliomas. These tumors begin in the brain or spinal cord and include astrocytomas, ependymoma, glioblastomas, oligoastrocytomas and oligodendrogliomas.
• Meningiomas. A meningioma is a tumor that arises from the membranes that surround your brain and spinal cord (meninges). Most meningiomas are noncancerous.
• Acoustic neuromas (schwannomas). These are benign tumors that develop on the nerves that control balance and hearing leading from your inner ear to your brain.
• Pituitary adenomas. These are mostly benign tumors that develop in the pituitary gland at the base of the brain. These tumors can affect the pituitary hormones with effects throughout the body.
• Medulloblastomas. These are the most common cancerous brain tumors in children. A medulloblastoma starts in the lower back part of the brain and tends to spread through the spinal fluid. These tumors are less common in adults, but they do occur.
• PNETs. Primitive neuroectodermal tumors (PNETs) are rare, cancerous tumors that start in embryonic (fetal) cells in the brain. They can occur anywhere in the brain.
• Germ cell tumors. Germ cell tumors may develop during childhood where the testicles or ovaries will form. But sometimes germ cell tumors move to other parts of the body, such as the brain.
• Craniopharyngiomas. These rare, noncancerous tumors start near the brain's pituitary gland, which secretes hormones that control many body functions. As the craniopharyngioma slowly grows, it can affect the pituitary gland and other structures near the brain.

Cancer that begins elsewhere and spreads to the brain

Secondary (metastatic) brain tumors are tumors that result from cancer that starts elsewhere in your body and then spreads (metastasizes) to your brain.

Secondary brain tumors most often occur in people who have a history of cancer. But in rare cases, a metastatic brain tumor may be the first sign of cancer that began elsewhere in your body.

Secondary brain tumors are far more common than are primary brain tumors.

Any cancer can spread to the brain, but the most common types include:

• Breast cancer
• Colon cancer
• Kidney cancer
• Lung cancer
• Melanoma