A brain tumor arises due to an abnormal growth of cells that have proliferated in an uncontrolled manner. The tumors are graded according to how aggressive they are, with lower-grade tumors often being benign and higher-grade tumors being malignant.
When normal cells grow old or get damaged, they either undergo programmed cell death (apoptosis) or get repaired. However, mutations can occur in the cellular DNA that disrupt these regulatory processes and cells that would normally die, go on to survive and proliferate. These cells multiply and give rise to more cells that all contain the abnormal DNA. Eventually, these accumulating cells form a mass called a growth or tumor.
Types of brain tumors
Brain tumors may be primary tumors, in which case they originate in the brain or secondary tumors that have spread to the brain from cancer elsewhere in the body. Low grade tumors (grade 1 or 2) are usually slow growing masses that are not likely to spread. These tumors are classed as benign because they usually stay confined to the site of origin and do not invade other parts of the body.
Unlike benign tumors, malignant brain cancers have the potential to spread to other tissues. Usually, malignant tumors are secondary tumors that have formed as a result of cancer spread. Primary malignant tumors tend to be high-grade (grade 3 or 4), aggressive cancers that grow quickly. These tumors require urgent treatment to prevent their invasion of other brain regions or the spinal cord.
Grades of tumors
Brain tumors are graded from 1 to 4, where grade 1 tumors are the slowest growing and least likely to spread and grade 4 tumors are the most aggressive and harmful cancers. Grade 1 and 2 cancers are usually classed as benign, whereas grade 3 and 4 tumors are classed as malignant.
Risk factors for brain tumors
A benign tumor arises form a abnormal cell growth that has started in the brain. The tumor grows slowly and does not usually spread. Benign tumors are sometimes congenital and caused by abnormal development in the womb. The causes of non-congenital tumors, however, are not clear.
Malignant brain tumors are usually caused by cancer in another part of the body that has spread to the brain. The cause of a primary malignant tumors, however, is not well understood.
Some genetic conditions can increase the risk of primary tumors, whether malignant or benign and examples include tuberous sclerosis, gorlin syndrome and neurofibromatosis. Such conditions can cause glial tissue tumors or gliomas. Other factors that have been suggested to increase the risk of brain tumors include radiotherapy, a family history of brain tumors and exposure to toxic chemicals such as formaldehyde. Researchers are also studying whether the radiofrequency energy emitted by cell phones damages brain tissue and increases the risk of brain tumors.
The symptoms of a brain tumor depend on its type, size and location. Tumors may not cause any symptoms at first but may eventually grow large enough to put pressure on parts of the brain and cause headaches, seizures or prevent the normal function of part of the brain.
Treatment of a brain tumor depends on its size and location. Although benign tumors do not tend to spread, they can cause damage by pressing on areas of the brain if they are not treated early. Grade 1 tumors can often be removed in a surgical procedure and the patient cured. However, grade 2 tumors often grow back and have the potential to mutate and turn into high-grade tumors.
A primary malignant tumor requires urgent treatment to prevent it spreading and causing damage to other parts of the brain and body. Treatment may involve surgery, radiation therapy and chemotherapy. However, these tumors often grow back once they have been surgically removed.
For patients with secondary brain tumors due to metastasized cancer, treatment is aimed at relieving symptoms, prolonging survival and improving quality of life.
Reviewed by Sally Robertson, BSc