Brain cancer is a term that describes a malignant, spreading growth of abnormal cells in the brain. The term is used only for malignant tumors – benign brain tumors are not brain cancer.
Brain cancer that originates in the brain, known as primary brain cancer, is relatively rare. More commonly, brain cancer originates elsewhere (lung, breast, prostate, or other locations) and spreads to the brain via the bloodstream or cerebrospinal fluid. That is known as a metastatic brain cancer, or secondary brain cancer.
Malignant tumors grow more quickly than benign tumors. A metastatic brain cancer that started as breast cancer, for example, will produce a brain tumor consisting of what looks like abnormal breast-cancer cells. A metastatic brain cancer that started as a malignant skin cancer will contain cells that look like the abnormal skin cells that were in the original cancerous skin growth.
Types of Primary Brain Cancer
Primary brain cancer will likely have originated from a glial cell, which make up half the cells in the brain and support the nerve cells, or neurons, that make up the other half of all the cells in the brain. A tumor that develops in a glial cell is known as a glioma. Gliomas, including glioblastomas, are the most common type of primary malignant tumors found in the adult brain. Glioblastoma multiforme (GBM) is the type of brain tumor that claimed the lives of Senator John McCain, Senator Ted Kennedy, Vice President Joe Biden’s son Beau Biden, and New York Mets baseball player Gary Carter.
Read Rod Nordland's remarkable survivorship story here
Primary brain cancer can spread from the original tumor in the brain to other parts of the brain or spine via the cerebrospinal fluid but generally does not spread outside the brain and spine.
Some types of primary brain cancers that grow from glial cells:
Types of Metastatic Brain Cancer
Unlike primary brain cancers, metastatic (secondary) cancers are tumors from elsewhere in the body that have spread to the brain. They are even able to pass through the filtering boundary known as the blood-brain barrier, which has evolved to keep toxins in the blood from entering the central nervous system. Certain cancers, like skin melanoma, lung, breast, kidney, and colon cancer are very good at being able to get through the blood-brain barrier. The new collection of cancer cells that has formed the malignant tumor in the brain can grow and put pressure on the surrounding structures in the brain and cause swelling, which leads to symptoms.
Some brain metastases appear long after the primary cancer has been diagnosed– even years later. Others grow and spread so quickly that they end up causing symptoms and are discovered before the primary cancer. Imaging scans, like an MRI or CT scan, may be done to find the site of the primary cancer. (A primary cancer that can’t be located is called an unknown primary cancer.) Treatment options vary depending on the location and number of new brain lesions along with the location and severity of the primary cancer.
Metastatic brain cancers are five times more common than primary brain cancer. As people survive primary cancers longer than they once did, there has been an increase in metastatic brain cancer. Up to half of all metastatic brain cancers originate from lung cancer. Other types of cancer that commonly spread to the brain include:
Cancer may spread to the leptomeninges (two of the three layers of membranes covering the brain and spinal cord). This is called leptomeningeal carcinomatosis (LC) or leptomeningeal disease (LMD). The most common cancers that spread to the leptomeninges are:
More about Metastatic Brain and Spine Tumors.
What Causes Brain Cancer?
Most brain cancers are secondary, or metastatic, meaning they result from the spread of a primary cancer. Researchers often can’t pinpoint what triggers the changes in the genes, or genetic mutations, that lead to primary cancers but are making progress. Some brain tumors are associated with genetic conditions, such as neurofibromatosis, von Hippel-Lindau disease, Li-Fraumeni syndrome, and retinoblastoma, that carry with them a higher likelihood of developing brain tumors. Some brain cancers may be caused by genetic mutations that result from exposure to environmental toxins, from previous radiation treatments for other cancers, or from other factors. For instance, excessive tanning/sunning can lead to malignant melanoma, which can metastasize and lead to brain cancer. Other substances known to cause cancer are:
For more information, visit our Neuro-oncology page
Reviewed by: Rohan Ramakrishna, MD
Last reviewed/last updated: August 2024
