What causes brain tumors?
Brain tumors can develop when genes in a cell are damaged and no longer function correctly. These genes normally regulate the rate at which the cell divides, repair genes that fix defects in other genes, and cause the cell to self-destruct if damage is beyond repair. Some patients may be born with a partial defect in one or more of these genes. Environmental factors can be affected by the mutated gene and cause further damage that results in a tumor. Environmental factors are the only cause of tumor formation in other patients. Brain tumors can also be caused by cancer in another part of the body that spreads to brain tissue, and grows a new tumor(s).
The body’s immune system would normally find the abnormal cell and kill it. However, the immune system may be defenseless because tumors can produce substances that block the immune response from being able to kill the abnormal cells.
Are there different types of brain tumors?
There are more than 150 different types of brain tumors, and they are classified into two groups: primary and secondary (or metastatic).
Primary brain tumors originate in the brain or in tissues close to it, such as the pituitary or pineal glands, or cranial nerves. When normal cells have mutations in their DNA (the cell’s instructions about what to do), the mutated cells can grow and divide rapidly, creating a mass of defective cells that form a tumor.
Primary tumors can be cancerous or noncancerous. A cancerous (malignant) tumor is more dangerous because it can grow quickly, spreading to other parts of the brain and spinal cord. A noncancerous (benign) tumor can press on other parts of the brain and cause damage. Benign tumors don’t spread, but occasionally they become malignant.
Primary brain tumors include:
- Gliomas begin in the brain or spinal cord, and are the most common type of adult brain tumor, accounting for 78% of malignant brain tumors.
- Meningiomas are tumors in the membranes that surround the brain and spinal cord (meninges). Most are not cancerous.
- Acoustic neuromas (schwannomas) are benign tumors that develop on the nerves that control balance and hearing. The nerves lead from the inner ear to the brain.
- Pituitary adenomas develop in the pituitary gland at the base of the brain, and can affect the pituitary hormones. This can cause symptoms throughout the body.
- Medulloblastomas are cancerous and most common in children, although they occur at all ages. Starting in the lower back part of the brain, they spread through the spinal fluid.
- Germ cell tumors are more common in children.
- Craniopharyngiomas are rare, and start near the pituitary gland, which secretes hormones that control many body functions. It can affect the pituitary gland and other structures near the brain.
Secondary brain tumors develop from cancer in another part of the body, usually through the bloodstream. They spread (metastasize) to the brain, where they form a new tumor(s). The most common types of cancer that spread to the brain are cancers of the breast, colon, kidney, lung and skin (melanoma). However, any cancer can metastasize to the brain.
Secondary brain tumors are always cancerous. They are more likely to develop in people who have a history of cancer. Secondary brain tumors are much more likely to develop in an adult, while children are more likely to develop a primary tumor.
Secondary brain tumors affect 25% of cancer patients. About 40% of people with lung cancer will develop a secondary brain tumor. In the past, patients typically survived only a few weeks after diagnosis. With better diagnostic tools, and improved surgical and radiation treatment methods, survival rates have been extended to several years and greatly improved quality of life for patients.
Who’s at risk for a brain tumor?
The cause of most primary brain tumors is unknown. However, certain factors can increase the risk, including exposure to ionizing radiation, which is the type of radiation caused by radiation therapy for cancer, or caused by atomic bombs. Risk is also increased if your family has a history of brain tumors.
