Brain tumors that begin in the brain:
Primary brain tumors occur in the brain itself or in tissues adjacent to it, such as the meninges (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 an increased rate and continue to live when healthy cells die. The result is a mass of abnormal cells that form a tumor.
In adults, primary brain tumors are much less common than secondary brain tumors, in which the cancer begins elsewhere and spreads to the brain.
There are many different types of primary brain tumors. Each gets its name from the type of cells involved.
Cancer that starts elsewhere and spreads to the brain
Secondary (metastatic) brain tumors are tumors that arise from cancer that begins 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 has started elsewhere in your body.
In adults, secondary brain tumors are much more common than primary brain tumors.