Related conditions:
Seizures, psychiatric symptoms (including abnormal personality and behavioral characteristics), loss of memory and cognition
Definition:
Brain and central nervous system (CNS) cancers are masses of abnormal cells (malignant tumors) in the brain and central nervous system that grow rapidly and can invade surrounding normal tissue. Brain tumors are named for both the type of cell from which they arose and their location in the brain. For example, schwannomas are named after the Schwann cells, astrocytomas after astrocytes, oligodendrogliomas after oligodendrocytes, meningiomas after the meninges or brain membranes, and pineoblastomas after the pineal gland. Exceptions are medulloblastomas, which are undifferentiated neuroectodermal tumors of the cerebellum, and central neuroblastomas, which affect the brain cortex. The naming system for pediatric brain tumors is still evolving and remains controversial.
Risk factors: Chemicals such as vinyl chlorides, aromatic hydrocarbons, and N-nitroso compounds in cigarettes; ionizing radiation; electromagnetic fields; and viral infections have been suggested as possible environmental risk factors. Some brain cancers appear to be more common in people working with radiation and chemicals, such as employees of nuclear plants and oil refineries. However, none of these environmental factors have been conclusively shown to cause brain cancer. Genetic risk factors include inherited diseases such as tuberous sclerosis and von Hippel-Lindau disease.
Etiology and the disease process: The causes of brain and CNS cancers are still unproven. Environmental, genetic, medical, and lifestyle factors may all play a role in causing these cancers. Brain tumors can be primary or secondary. Primary tumors originate in the brain and are rarer than secondary brain tumors. Once they occur, primary brain tumors rarely metastasize to other tissues beyond the spinal cord. Examples of primary brain tumors are schwannomas, astrocytomas, medulloblastomas, meningiomas, and oligodendrogliomas. Secondary or metastatic tumors originate elsewhere in the body and migrate or metastasize to the brain. The types of cancer most likely to metastasize to the brain are breast cancer, lung cancer, melanoma, and colon cancer. Nasopharyngeal cancer can also metastasize to the brain via the cranial nerve or through openings in the bone at the base of the skull, called foramina.
Incidence: The annual incidence of CNS tumors in the United States between 2007 and 2011 was 6.4 per 100,000 people, with an estimated 4.3 deaths per 100,000 people annually, according to the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) Program. Approximately 23,380 new cases of brain and central nervous system cancers occurred in the United States in 2014, as well as an estimated 14,320 deaths from these cancers. Brain tumors account for 85 to 90 percent of all primary CNS tumors. Incidence rates of primary brain tumors are highest in people of Caucasian descent and are higher in men (7.6 per 100,000) than in women (5.4 per 100,000). Brain tumors are most common in people older than fifty-five, with a median age at diagnosis of fifty-seven. However, they can occur at any age.
Primary brain tumors are rarer than secondary brain tumors. The ratio of secondary to primary brain tumors is thought to be at least 3:1, although precise statistics are unavailable. According to the Central Brain Tumor Registry of the United States (CBTRUS) 2013 statistical report, the most common primary brain tumors are meningiomas and glioblastomas, which together make up 51.4 percent of all primary brain tumors. The next most common are pituitary tumors (14.7 percent), nerve sheath tumors (8.1 percent), and astrocytomas (6.1 percent). The most common primary spinal tumors are schwannomas, meningiomas, and ependymomas, accounting for approximately 79 percent of primary spinal tumors, as reported by the National Cancer Institute.
Secondary brain tumors occur in approximately one-fourth of all metastatic cancers. About 85 percent of secondary tumors occur in the cerebrum and 15 percent in the cerebellum, according to the American Brain Tumor Association in 2012. Multiple metastases in the brain are more common than solitary metastases, occurring in more than 80 percent of cases.
Symptoms: Symptoms of brain tumors include persistent headaches that become more intense and frequent, seizures, problems walking and speaking, vision problems (including blurred vision, double vision, or loss of peripheral vision), loss of memory and cognition, personality or behavioral changes, abnormal breathing rates, dizziness, nausea or vomiting, loss of hearing, and hormonal disorders.
In one study of brain tumors and seizures, seizures were observed in more than 38 percent of patients with primary brain tumors and in 20 percent of patients with cerebral metastases. Oligodendrogliomas are more likely than other types of CNS tumors to be associated with seizures.
Screening and diagnosis: The first step of brain-tumor screening involves a neurological exam to test vision, hearing, balance, coordination, and reflexes. If the neurological exam results warrant further testing, the doctor may order brain-imaging scans, such as computed tomography (CT) and magnetic resonance imaging (MRI) scans, which produce pictures of the brain in which tumors can be distinguished by means of dyes or magnetic fields. Computed tomography is better at detecting bone calcification and skull lesions; magnetic resonance imaging is better for detecting soft-tissue and spinal cord tumors. Other possible tests include an angiogram, in which a dye is injected into the blood to highlight the blood vessels in and around the brain; x-ray scans of the head and skull to reveal changes to skull bones and calcium deposits associated with brain tumors; and positron emission tomography (PET), which identifies areas of abnormal brain metabolism. The discovery of genetic mutations (changes in specific genes) that are linked to different types of cancers has opened the door to future genetic screening for at-risk individuals. A genetic screen involves taking a blood sample and analyzing the deoxyribonucleic acid (DNA) in the sample for genetic mutations that are known to cause a specific type of cancer.
When a tumor is detected on a brain scan, a biopsy is usually performed to make a diagnosis. A biopsy involves taking a sample of the tumor; this can be done in a separate procedure or during surgery to remove the tumor. The tumor can be biopsied by open craniotomy, in which the cranium or skull is opened to expose the brain, allowing a sample of the tumor to be surgically removed. Hard-to-reach tumors can be sampled by means of a needle biopsy. A small hole, known as the “burr” hole, is drilled in the cranium, and tumor cells are extracted with a narrow-bore needle. The tumor sample is frozen and cut into very thin slices, which are then examined under a microscope. This allows the medical team to confirm the presence of a tumor and determine the specific type of tumor. Additional tests may also be performed to help pinpoint the tumor type.
There is no standard method for staging brain tumors. A brain tumor is classified according to the tumor grade, the type of cell from which it originated, and its location in the central nervous system. The World Health Organization (WHO) grades CNS tumors on a scale from I to IV. Grade I tumors grow slowly and rarely spread to other tissues. The following types of brain tumors are classified as grade I: pilocytic astrocytomas, grade I meningiomas, and grade I ependymomas. Grade II tumors typically grow slowly but may spread to other tissues. These include diffuse astrocytomas, grade II meningiomas, oligodendrogliomas, grade II ependymomas, oligoastrocytomas (made up of a mixture of oligodendrogliomal and astrocytomal cells), pinealcytomas, and craniopharyngiomas. Grade III tumors contain fast-growing cells that often spread to other tissues and include anaplastic astrocytomas, anaplastic oligodendrogliomas, anaplastic ependymomas, anaplastic oligoastrocytomas, and pinealoblastomas. Grade IV tumors grow rapidly, spread aggressively, and contain cells that appear very different from normal cells. Grade IV tumors include gliobastomas and medulloblastomas, which usually occur in children and adults aged twenty-one to forty.
Treatment and therapy: The most common treatment for brain and central nervous system cancers involves surgery to remove as much of the tumor as possible without disrupting neurological function. Surgery usually does not result in the removal of all tumor tissue. In addition, some tumors are located deep in the brain and cannot be reached without considerable damage to the surrounding tissue. These tumors are sometimes diagnosed without conducting a biopsy and treated by nonsurgical means. Radiation treatment and chemotherapy can be used to remove cancer cells remaining after surgery and to treat deep-seated tumors that are not amenable to surgical removal. Radiation therapy is effective for a wider range of brain and spinal cord tumors than chemotherapy. Radiation can enhance the cure rate and prolong disease-free survival. A common type of radiation treatment is external beam radiation therapy (EBRT). Chemotherapy has been shown to prolong disease-free survival in patients with gliomas, medulloblastomas, and some germ-cell tumors. Chemotherapy agents include dexamethasone, mannitol, furosemide, and nitrosourea. Anticonvulsants are also used to treat cancer patients with seizures.
The majority of brain tumors are accompanied by multiple metastases. These can be treated with a combination of surgery or radiosurgery and whole-brain radiation therapy (WBRT). Radiosurgery is useful for lesions that have a diameter smaller than three centimeters. Corticosteroids and anticonvulsants can also be used as needed. Chemotherapy is not as widely used for metastatic brain tumors but may be effective for brain metastases from chemosensitive primary tumors.
New therapies being tested include tyrosine kinase receptor inhibitors, farnesyl transferase inhibitors, viral-based gene therapy, and oncolytic viruses. Patients with tumors that do not respond well to the commonly used treatments can look into clinical trials using novel therapies combined with EBRT.
Surgery to remove brain tumors can sometimes result in damage to normal brain tissue, which can cause partial paralysis, changes in sensation, muscle weakness, and defects in thinking and language function. These patients may be referred for physical and speech therapy to regain muscle and language functions, respectively. Follow-up visits are an important part of patient care and usually occur every three to four months for the first two to three years after treatment, then once or twice a year after that. The doctor will discuss treatment side effects, review medical history, and conduct various tests to determine if the cancer has recurred or metastasized to other parts of the body.
Prognosis, prevention, and outcomes: A cancer patient’s prognosis depends on age (whether younger or older than sixty), the number and location of tumors in the brain and spinal cord, the rate of tumor growth and metastasis, and the tumor’s response to treatment. The prognosis is better for brain metastases from breast cancer and worse for brain metastases from colon cancer. When doctors discuss survival rates, they are referring to the percentage of people with a specific type and stage of cancer who survive for a predetermined period of time after their diagnosis. A common statistic is the five-year survival rate. Doctors may talk about the percentage of people who are alive, the percentage who are symptom-free, or the percentage who are disease-free five years after diagnosis. These numbers are averages for large groups of people and do not predict the specific outcome for an individual patient.
Because the causes of brain and central nervous system cancers are not well established, prevention strategies are still evolving. As with other cancers, quitting smoking, maintaining a healthy diet, and exercising are likely to have beneficial and preventive effects. A novel therapy that is undergoing clinical trials is DCVax-L, a treatment for glioblastoma multiforme that involves vaccination with dendritic cells that recognize molecules on an individual patient’s tumor cells.
When examining outcomes for brain cancer survivors, it is important to also consider their quality of life. A survivor’s quality of life has been directly linked to cognitive impairment, especially defects in speech and language.
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