Primary brain tumors develop within brain tissue. Such tumors can spread throughout the brain, but they are not always cancerous, or malignant.
Malignant brain tumors can originate in the brain or spread to the brain from other parts of the body, a condition that becomes potentially lethal. The likelihood to grow faster and invade, coupled with the identification of specific cells within the tumor, are some of the criteria used to classify the tumor’s severity, or grade. No matter what grade a brain tumor is assigned — and whether it’s malignant or not — these growths are always serious because they can interfere with normal brain activity.
Brain tumors can be either primary or metastatic. Primary brain tumors arise within the brain, whereas metastatic (also called secondary) brain tumors spread from other parts of the body through the bloodstream and enter the brain. The incidence of primary brain tumors is about 19 cases per population of 100,000. About 35,000 new cases occur in the United States annually.
Tumor symptoms and treatment options
Symptoms of brain tumors vary according to the tumor’s location and size, but seizures and headaches are among the most common. In particular, gliomas, typically malignant brain tumors, release the neurotransmitter glutamate at toxic concentrations. The glutamate kills off neurons near the tumor, making room for its expansion. The released glutamate is largely responsible for the seizures, which originate from tissue surrounding the tumor. An expanding tumor can increase pressure within the skull, causing headache, vomiting, visual disturbances, and impaired mental functioning. Brain tumors are diagnosed with MRI and CT scanning. Early imaging is beneficial because it can mean that tumors are identified at a lower grade, improving prognosis and outcome considerably.
Treatment options for primary brain tumors are limited. Surgery is generally the first step if the tumor is accessible and vital structures will not be disturbed. Radiation is used to stop a tumor’s growth or cause it to shrink. Chemotherapy destroys tumor cells that may remain after surgery and radiation, but it is not very effective for gliomas, largely because it is hard for chemotherapeutic drugs to reach the brain. Steroid drugs relieve brain swelling and antiepileptic drugs control seizures.
Next generation therapies
New therapies for brain tumors are being developed in clinical trials. Many of these trials focus on targeted therapy — treatment aimed at the biologic characteristics of tumors. Targeted therapies include vaccines created from the patient’s own tumor combined with substances that boost the immune system or kill tumor cells; monoclonal antibodies, which home in on receptors on the surface of the tumor cells; anti-angiogenic therapy, during which the tumor’s blood supply is restricted; immunotherapy, which uses the body’s own immune system against the tumor; gene therapy, which delivers bioengineered genes to the cancer cells to kill them; and several approaches for a targeted delivery of antibodies, toxins, or growth-inhibiting molecules that attach specifically to the tumor cells and interfere with their growth. A scorpion-derived toxin called chlorotoxin, which interferes with the spread of the tumor, has shown promise in clinical studies. This therapy extended life expectancy significantly.
Researchers are exploring the role of stem cells in the origin of brain tumors, and brain tumor research is being strongly influenced by the wealth of research into neural stem cells in particular. As the identification of the cellular components that make up different tumors becomes easier (due to genomics technology and neural stem cell research), scientists will be able to better target the cells in the tumor that are most likely to be the most harmful. Epidemiologists, or scientists studying disease in human populations, also are looking into tumor genetics and patients’ lifestyles, environments, occupations, and medical histories for clues about the causes of these tumors. International efforts are underway to increase awareness of brain tumors, encourage research collaboration, and explore new and innovative therapies.