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Patients diagnosed with a brain tumor can have widely varying life expectancies. A number of factors are important in determining a patient's prognosis. First, the type of cancer present is very important, as different types of malignant growths have varying degrees of aggressiveness. The size and location of the tumor at the time of diagnosis are also important. Another relevant factor in brain tumor prognosis is whether the primary tumor has metastasized, or spread, to regions of the body far away from the brain.
One important factor that affects brain tumor prognosis is the type of tumor present. Many different cells located within the brain can develop into cancerous growths, and the resultant tumors have varying abilities to increase in size and spread to other areas of the body. For example, one type of brain tumor called a glioblastoma multiforme (GBM) is very aggressive, and patients diagnosed with this tumor typically survive for less than a year. In contrast, a meningioma, which is a tumor derived from the membranes lining the brain, grows much more slowly and is less likely to metastasize to other areas of the body. Patients who receive this cancer diagnosis have a longer life expectancy.
Another important aspect of brain tumor prognosis is the size of the tumor at the time of diagnosis. In general, tumors that are larger have a worse prognosis than tumors that are smaller. This is because these larger tumors have had more time to grow, spread, and entangle themselves into the important structures of the brain. Big tumors located in the brain can be especially dangerous because there is limited room available within the skull. Excessive tumor growth could cause herniation — or shifting — of the brain outside of the cranium, a process that could result in loss of consciousness and cessation of breathing.
In contrast to many other types of tumors that affect different organs in the body, the location of the brain tumor can greatly affect the patient's prognosis. This is due to the fact that regions of the brain are highly specialized in their abilities to control aspects of the body's operation. A brain tumor affecting the brain stem could be deadly because this region of the brain controls vital processes such as breathing, the beating of the heart, and the circulation of the blood. One located in the frontal lobe of the brain might only cause personality changes, and might not be immediately life-threatening.
Whether the tumor has metastasized also affects brain tumor prognosis. Cancerous cells can spread from the brain to other regions of the body through the lymphatic system or the blood. Although brain tumors do not metastasize as frequently as some other tumors in the body, if they do spread to distant areas then the patient's prognosis is fairly poor. Of note, other tumors such as lung cancer, breast cancer, or colon cancer often metastasize to the brain region. In general, having brain metastases is a poor prognostic sign for patients with these other cancers.