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Types of Brain Cancer and Brain Tumors

The brain is the most complex organ in the human body. It controls the central nervous system (CNS), the peripheral nervous system, and regulates virtually all activity including involuntary actions such as heart rate, respiration, and digestion; as well as voluntary or conscious, more complex mental activity such as thought and reason.

The brain can be divided into three main parts: the cerebrum, cerebellum, and the brain stem. Each area is responsible for different brain functions, although there is some overlap.

About  Brain Tumors

A brain tumor is defined as any abnormal or uncontrolled growth of cells in the brain. Tumors can be either benign, meaning non-cancerous, or malignant, meaning they may be cancerous. However, because they are located in the brain, it is important to recognize that even a benign brain tumor can be dangerous. As a tumor in the brain grows, it presses upon normal brain tissues which can cause inflammation and brain swelling. It is therefore very important that both benign and malignant brain tumors be treated as early as possible.

A primary brain tumor results when a tumor originates in the brain itself. When cancer metastasizes - or spreads from other areas, such as the lungs or the breasts - to the brain, a secondary (or metastatic) brain tumor results. Brain tumors are less common than other cancers, but they are considered to be dangerous due to their location and sometimes aggressive nature.


Classification of Brain Tumors

Benign Brain Tumors

Benign brain tumors are non-malignant. They usually - but not always - can be removed, and are not likely to recur. Benign brain tumors have clear borders. These tumors do not invade nearby tissue, however, they can press on sensitive areas of the brain and cause symptoms.

Malignant Brain Tumors

Malignant brain tumors contain cancer cells and interfere with vital functions. Malignant brain tumors are likely to grow rapidly and crowd or invade the tissue around them. Like a plant, these tumors may put out "roots" that grow into healthy brain tissue. If a malignant tumor remains compact and does not have roots, it is said to be encapsulated. When an otherwise benign tumor is located in a vital area of the brain and interferes with vital functions, it may be considered malignant (even though it contains no cancer cells).

Primary brain tumors are classified by the type of tissue in which they begin. The most common primary brain tumors are gliomas, which begin in the glial (supportive) tissue. There are several types of gliomas:
  • Glioblastoma multiforme (GBM) is the most common and aggressive type of primary brain tumor, accounting for 52% of all primary brain tumor cases and 20% of all intracranial tumors. Despite being the most prevalent form of primary brain tumor, GBMs occur in only 2-3 cases per 100,000 people in Europe and North America. Treatment can involve chemotherapy, radiotherapy, and surgery, all of which are acknowledged as palliative measures, meaning that they do not provide a cure. Even with complete surgical resection of the tumor, combined with the best available treatment, the survival rate for GBM remains very low. However, many advances in microsurgery techniques, radiotherapy and chemotherapy are slowly increasing the survival time of patients diagnosed with glioblastoma.

  • Astrocytomas arise from small, star-shaped cells called astrocytes. They may grow anywhere in the brain or spinal cord. In adults, astrocytomas most often arise in the cerebrum. In children, they occur in the brain stem, the cerebrum, and the cerebellum. A grade III astrocytoma is sometimes called anaplastic astrocytoma. A grade IV astrocytoma is usually called glioblastoma multiforme.
  • Anaplastic astrocytoma is a high-grade, or malignant, glioma, a tumor of the glial (supportive) tissue of the brain.
  • Brain stem gliomas occur in the lowest, stem-like part of the brain. Tumors in this area generally cannot be removed. Most brain stem gliomas are high-grade astrocytomas.
  • Ependymomas usually develop in the lining of the ventricles. They may also occur in the spinal cord. Although these tumors can develop at any age, they are most common in childhood and adolescence.
  • Oligodendrogliomas arise in the cells that produce myelin, the fatty covering that protects nerves. These tumors usually arise in the cerebrum. They grow slowly and usually do not spread into surrounding brain tissue. Oligodendrogliomas are rare and occur most often in middle-aged adults, but they have been found in people of all ages.
  • Anaplastic oligodendrogliomas are uncommon primary brain tumors. The majorityof these lesions arise in adults with a mean age at operation of 48.7 years and have a slight male predominance. Mean survival time following medical and surgical intervention is 3-4 years, with 5- and 10-year survival rates of 41% and 20%, respectively. Risk of malignant progression is thought to correspond to the astrocytic component of the tumor. Factors to confer more favorable outcome include young age, chromosomes 1p and 19q deletion, frontal location, gross total surgical resection, and post-operative Karnofsky score.

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There are other types of primary brain tumors that do not begin in glial tissue. Some of the most common are:

  • Pituitary tumors are abnormal growths of pituitary cells. They can either be nonfunctional (do not secrete hormones) or produce specific hormones, such as prolactin (causing infertility, decreased libido, and osteoporosis), growth hormone (causing acromegaly), ACTH (causing Cushing's) and TSH (causing hypothyroidism).
  • Primary Central Nervous System Lymphoma is a rare cancer that involves the central nervous system. The designation as a "lymphoma" reflects the fact that the cancerous cells are lymphocytes, a type of white blood cell. Primary CNS lymphoma affects all age groups, but is most commonly diagnosed in persons who are over 50 years of age. In addition, individuals who are immunosuppressed (have reduced functioning of the immune system) such as patients with AIDS or those taking certain drugs after organ transplantation, appear to be at increased risk.
  • Medulloblastomas. Recent research suggests that these tumors develop from primitive (developing) nerve cells that normally do not remain in the body after birth. For this reason, medulloblastomas are sometimes called primitive neuroectodermal tumors (PNET). Most medulloblastomas arise in the cerebellum, but they may occur in other areas as well. These tumors occur most often in children and are more common in boys than in girls.
  • Meningiomas grow from the meninges and are usually benign. Because these tumors grow very slowly, the brain may be able to adjust to their presence. Meningiomas often grow quite large before they cause symptoms. They occur most often in women between 30 and 50 years of age.
  • Schwannomas are benign tumors that begin in Schwann cells, which produce the myelin that protects the acoustic nerve - the nerve of hearing.
  • Acoustic neuromas are a type of schwannoma, a non-cancerous tumor that develops on the nerve that connects the ear to the brain. The tumor usually grows slowly, pressing against the hearing and balance nerves. Symptoms may be mild or non-existent at first, and can include loss of hearing on one side, ringing in ears or dizziness and balance problems. They occur mainly in adults and affect women twice as often as men.
  • Craniopharyngioma is a tumor that develops in the area of the brain called the hypothalamus, which is close to the pituitary gland. It is usually found in children or young adults and accounts for around 10% of all brain tumors in young people, though it can be diagnosed at any age. Craniopharyngiomas are nearly always benign, but can cause symptoms once they press upon other parts of the brain around them. They are often quite large when they are detected, ranging in size from one to more than four inches in diameter. Craniopharyngiomas develop in the region of the pituitary gland near the hypothalamus. They are usually benign; however, they are sometimes considered malignant because they can press on or damage the hypothalamus and affect vital functions. These tumors occur most often in children and adolescents.
  • Germ cell tumors arise from primitive (developing) sex cells, or germ cells. The most frequent type of germ cell tumor in the brain is the germinoma.
  • Pineal region tumors occur in or around the pineal gland, a tiny organ near the center of the brain. The tumor can be slow growing (pineocytoma) or fast growing (pineoblastoma). The pineal region is very difficult to reach, and these tumors often cannot be removed.
  • Colloid cysts are cysts containing gelatinous material in the brain. Because of their location, these cysts can cause obstructive hydrocephalus and increased intracranial pressure. They account for approximately 1% of all intracranial tumors. Symptoms can include headache, vertigo, memory deficits, diplopia and behavioral disturbances.
  • Chordoma is a rare malignant tumor that arises from notochord remnants. Chordomas account for 1 to 4% of all bone tumors. They occur in older adults with the highest prevalence in the fifth to seventh decade. The ratio of male to female is two to one.

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Tumor Grade

Some brain tumors are referred to by grade - from low grade (grade I) to high grade (grade IV). The grade of a tumor refers to the way the cells look under a microscope. Cells from higher grade tumors are more abnormal looking and generally grow faster than cells from lower grade tumors; higher grade tumors are more malignant than lower grade tumors.

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Tumor-Specific Statistics

Metastatic brain tumors are the most common brain tumor, with an annual incidence more than four times greater than that of primary brain tumors. The cancers that most commonly metastasize to the brain are breast and lung cancers.

  • Meningiomas represent 24% of all primary brain tumors, making meningiomas the most common primary brain tumor.
  • Glioblastomas represent 23% of all primary brain tumors.
  • Astrocytoma and pituitary tumors each represent 8% of all primary brain tumors.
  • Nerve sheath tumors (such as acoustic neuromas, vestibular schwannomas, neurilemmomas) represent 6% of all primary brain tumors.
  • Anaplastic astrocytomas and lymphomas each represent 4% of all primary brain tumors.
  • Oligodendrogliomas represent 3% of all primary brain tumors.

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Support

Led by Karen Shires, RN, OCN, the Brain Tumor Support Group at Emory provides a comfortable setting for patients, families, friends and caregivers to share their experiences, learn about current therapies, hear interesting speakers who provide information about all aspects of diagnosis and treatments.

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Sources:
American Brain Tumor Association
The Brain Tumor Society
National Cancer Institute (NCI)
National Brain Tumor Foundation
Wikipedia.org