Part One - The Basics

1.  What is a brain tumor?

2.  Why are there so many different types of brain tumors?

3.  Can any part of the brain have a tumor?

4.  How common are brain tumors?

5.  What causes a brain tumor?

6.  Are brain tumors inherited?

Tables:  Occupations Associated with Increased Risk of Brain Tumors

                Genetic Syndromes Associated with Brain Tumors

Copyright © 2003 by Jones and Bartlett Publishers, Inc.

All rights reserved. No part of the material protected by this copyright notice may be reproduced or utilized in any form, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission from the copyright owner.

1.  What is a brain tumor?

The human brain is usually thought of as a single organ, a living computer that receives information from the senses and directs responses to our internal organs and muscles. Actually, the brain is only one part of the central nervous system (CNS), which also includes the spinal cord and the meninges, the three layers surrounding the brain and spinal cord.  Like the other organs of the body, the central nervous system is composed of individual cells. These cells differ in their structure and function, but all have a normal function, directed by deoxyribonucleic acid (DNA), the internal genetic material of the cell nucleus. Occasionally, the genetic material develops a mutation or error that disrupts the function of the normal cell. If this abnormal cell continues to grow, divide, and produce more abnormal cells, the mass of abnormal cells may eventually become a visible tumor. In the brain, an enlarging mass of abnormal cells that have "forgotten” their original function may disturb the surrounding normal cells in several ways:

    · The tumor may create pressure on a section of nearby normal brain, pushing the brain against the skull.

    · The tumor may obstruct the flow of blood or spinal fluid circulating in the brain.

    · The tumor may spread into the spinal fluid, creating more tumors in the brain and spinal cord. 

The word “tumor” as used above is not specified as benign or malignant or noncancerous and cancerous. For some brain tumors, there is not a perfect distinction between these terms. Whereas benign tumors are often characterized as slow-growing or unlikely to spread within the brain, some “benign” tumors cannot be removed surgically and, therefore, cause severe disability and death. Other benign tumors appear to develop further genetic damage over time and become even more rapidly growing masses, a process called malignant transformation. Malignant brain tumors tend to grow rapidly, damaging normal brain cells in the surrounding area. They may spread into other areas of the brain, spinal fluid, meninges, or spinal cord. Unlike malignant tumors of the breast, lung, colon, and other organs, malignant tumors of the brain rarely spread to other organs of the body. While "benign" tumors can be dangerous, a few malignant tumors can also be cured.

There are over 100 different types of tumors that originate in the brain, the spinal cord, or the meninges. Throughout this book these tumors will be called primary brain tumors. However, many cancers originate in other organs of the body and can spread through the blood stream to the brain, forming a tumor that is identical to the original tumor. These tumors are called metastatic or secondary brain tumors. Some patients have brain metastases many years after the diagnosis of cancer. Some patients have brain metastases even before they know they have cancer.

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 2.  Why are there so many different types of brain tumors?

To understand why there are so many types of brain tumors, it is necessary to learn some basic facts about normal brain cells. The neurons are cells that send electrical and chemical signals to other neurons. They perform the "work" of the nervous system. It is estimated that there are 1,000,000,000,000 (1 trillion) neurons, each with as many as one thousand different connections to other neurons. The glial cells, which outnumber neurons nine to one, support the neurons. Some glial cells make myelin, an insulating sheath that allows neurons to conduct electrical signals at high speed. Some glial cells separate groups of neurons from each other, and some line the spinal fluid spaces of the brain. The major types of glial cells include astrocytes, oligodendrocytes, and ependymal cells.

How a normal cell becomes genetically damaged is not known, but the damage apparently causes the cell to divide repeatedly, producing a mass of cells.  The most common brain tumor in adults is astrocytoma, which is not surprising considering that the majority of cells in the brain are astrocytes. Similarly, abnormal oligodendrocytes that grow into a tumor become oligodendrogliomas, and abnormal ependymal cells become ependymomas. All of these tumors may be either benign (as the term is used above, slow-growing) or malignant (fast-growing, destructive). The names of many types of brain tumors are derived from their normal cell or tissue of origin, with the addition of the suffix "-oma." For example, tumors involving meninges are called meningiomas; tumors of the glial cells are called gliomas, tumors involving schwann cells are called schwannomas.   

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3.  Can any part of the brain have a tumor?  Where do most brain tumors occur in

the brain? Are there areas of the brain where it is more dangerous to have a tumor?

Both benign and malignant tumors can occur in all parts of the body, and the brain is no exception. The central nervous system includes the three major sections of the brain, the cerebrum, the cerebellum, the brain stem; and the spinal cord (Fig. 1). The cerebrum, the largest part of the brain, is divided into right and left hemispheres, which connect across the middle at the corpus callosum. The outer surface of the hemispheres, the cortex, is often called gray matter. It is slightly gray because of the dense population of cells packed into its convolutions (the ridges on the surface). At first glance, the cerebral hemispheres seem to have only a random collection of crevices and bulges, but there are deep folds or fissures that separate each hemisphere into lobes. Each cerebral hemisphere is subdivided into the frontal lobe, the temporal lobe, the parietal lobe, and the occipital lobe. Directly under the occipital lobe at the back of the head is the cerebellum, which is also divided into two hemispheres. The brain stem is a knob-like structure that is located in front of the cerebellum and under the cerebrum. The lower end of the brain stem is continuous with the spinal cord. Two elongated, curved openings in each cerebral hemisphere, called the lateral ventricles, connect with two slit-like openings in the center of the brain, called the third and fourth ventricles (Fig. 2). Spinal fluid is produced in the choroid plexus, two spongelike tissues in the lateral ventricles. A tumor can occur in any of these parts of the brain, spinal cord, and meninges.

The symptoms of tumors vary with the location of the tumor. The grade influences how rapidly a tumor will cause symptoms. Grade refers to how much the tumor appears to resemble normal brain under the microscope. Low-grade tumors typically have few cells that are dividing at any one time. A high-grade tumor has a rapid growth rate, and the cells may appear disorganized and distorted. There are, of course, tumors that are somewhere in between these two extremes. These tumors are called intermediate-grade tumors.

The cerebral hemispheres direct motor function to the opposite site of the body, but the cerebellum, which coordinates movement, affects the same side of the body. For example, in most right-handed people the left hemisphere controls speech as well as motor function to the right side of the body, so the left hemisphere is considered the dominant hemisphere. However, some left-handed people are also considered left-hemisphere dominant because their speech center is located in the left hemisphere.

The frontal lobes of the cerebral hemispheres govern emotion, thought, reasoning, behavior, and memory. The ability to articulate speech is controlled by the dominant frontal lobe. The parietal lobes control sensory and motor information and the dominant parietal lobe is responsible for understanding written and spoken language. The temporal lobes contain both auditory and visual pathways, and interpret sounds and spoken language for long-term memory. The occipital lobes interpret visual images, as well as the meaning of written words. 

The cerebellum controls balance and coordination, affecting movements of the same side of the body. The brain stem is responsible for a number of "unconscious" activities, including breathing, heart rate, swallowing, wakefulness, and sleep. Many of the cranial nerves, the nerves that provide motor and sensory function to the eyes, mouth, tongue, neck, and shoulders arise from the brain stem. The brain stem is continuous with the spinal cord, with the boundary between the two set at the foramen magnum, the large hole at the base of the skull.

The cerebral hemispheres make up the largest mass of the central nervous system, and; most of the primary brain tumors affecting adults occur in this area. In children, primary brain tumors more often affect the cerebellum and brain stem. Spinal cord tumors are relatively uncommon in both age groups. 

The brain stem and cranial nerves are surrounded by the base of the skull, which has numerous small openings for the blood vessels and nerves that travel to and from the brain. However, the space within the skull is limited. An expanding tumor that exerts pressure on the brain stem may affect consciousness, heart rate, and breathing. Tumors in this area are also more difficult to remove without injuring the normal brain structures and blood vessels. Although all tumors can cause symptoms, tumors that directly or indirectly affect the brain stem are some of the most difficult and dangerous to treat. 

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4.     How common are brain tumors? Is it true that brain tumors are more common in children than in adults?

About 1,200,000 adults in the United States are diagnosed with cancer every year, and of those, 35,000 will have a primary brain tumor. Almost half of primary brain tumors are malignant. Primary brain tumors account for only about 2% of all cancers in adults, and with the many different types of brain tumors, some forms are very rare.

In the United States, 8,600 children ranging from birth to age 14 are diagnosed with cancer each year. Brain tumors account for about 20% of all cancers in children (about 1,800 cases). However, the risk of developing a brain tumor increases with age. A person is four times more likely to develop a brain tumor at age 55 than at age 12, and ten times more likely to develop a brain tumor at age 75 than at age 35. The national cancer registry has reported a steady increase in the incidence of brain tumors over the last 20 years, particularly in the elderly population. Part of this increase appears to be related to the improved detection of brain tumors with computed tomography (CT) and magnetic resonance imaging (MRI) scans.

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5.     What causes a brain tumor?

Because there are so many different types of brain tumors, each originating from the different types of cells within the brain, spinal cord, or meninges, it is impossible to determine a cause for most brain tumors. There are, however, known risk factors for the development of some types of tumors.

Cigarette smoking has not been clearly associated with an increased risk for the development of primary brain tumors, but smoking is an important cause of metastatic brain tumors, particularly those that originate from lung cancer. Of the 170,000 lung cancer patients diagnosed each year in the United States, about one-third will develop one or more tumors in the brain -- more than 55,000 people! 

There are some primary brain tumors that affect men more commonly than women and vice versa, but the reasons for these differences are not known. There are also some studies suggesting that workers in certain occupations have a higher incidence of brain tumors. Table 1 lists occupations that have been associated with an increased risk of brain tumors.  The increased risk is expressed as an odds ratio (OR).  The odds ratio is found by dividing the odds of being in a specific occupation and having a brain tumor, by the odds of being in the occupation but not having a brain tumor. For many occupations studied, there was no known exposure to a potential cancer-causing chemical. Some researchers have suggested that patients with professional or highly paid jobs have better access to medical care, which may result in a greater number of brain tumors diagnosed.  However, it is interesting to note that in Sweden, where there is universal access to free medical care, some occupations are still observed to have a higher risk of brain tumors. These include medical professionals, biologists, agricultural research scientists, and dentists.

Table 1. Occupations Associated with Increased Risk of Brain Tumors

Patients who have previously had radiation therapy to the brain, skull, or scalp are at risk for developing brain tumors many years later. Several studies have investigated other sources of radiation, such as electromagnetic fields, power lines, and cell phones.  However, studies have not yet proven that these sources cause brain tumors.

Head injury, hair dye, and drug use have also been studied, but it has not been shown conclusively that these factors cause primary brain tumors. Food additives and preservatives and chemicals in drinking water have been studied in a number of countries. For example, eating preserved, smoked, or pickled meat and fish appears to correlate with an increased risk of brain tumors. In addition, two studies have shown that the risk of brain tumor decreases when individuals eat more fruits and vegetables. However, other studies of dietary influence on the development of brain tumors have been inconclusive. 

In summary, though many factors have been studied for a possible link to the development of primary brain tumors, few are considered definite risk factors.

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6.     Are brain tumors inherited?

There are some genetic diseases that are clearly associated with the development of specific brain tumors. Fortunately, most of these are rare. Whereas only about 5% of brain tumor patients have a family member with the same or a very similar brain tumor, about 19% of all brain tumor patients have a close family member with another type of cancer. This suggests that the tendency to develop genetic damage that causes abnormal cell growth may be inherited, but the tendency to develop a specific tumor may not be inherited. 

Table 2 lists genetic syndromes that have been associated with brain tumors.  A brain tumor may contain one or multiple mutations, but that does not mean that the abnormal gene containing the mutation will be inherited by the patient’s children.  Only those abnormal genes that are present in the reproductive cells (eggs and sperm) are inherited. In many of the syndromes listed, more than one type of cancer has been described.  In Turcot’s syndrome, for example, all patients who inherit the gene will develop colon cancer if untreated. Because of more widespread genetic testing, many families who are affected by one of the genetic syndromes shown below are aware of their increased cancer risk.

Table 2.  Genetic Syndromes Associated with Brain Tumors

Sporadic mutations (those that develop spontaneously and are not present in the reproductive cells) account for more than 95% of all brain tumors.  However, some of the same mutations described in inherited brain tumors also occur in tumors arising spontaneously.  The p53 mutation, for example, is found in over 50% of all human cancers.  For reasons that are unclear, younger patients with glioblastoma are more likely to have a p53 mutation than older patients.

 M.L.'s comment:

It was June 28, 2000 when I found out that I had a brain tumor. That day was supposed to be just like any other day, but when my alarm went off I woke up feeling like I had the flu, and I just wanted to go back to sleep. I remember I didn't sleep well the night before. I just kept tossing and turning. I felt like I never really went to sleep all night. I hadn't ever had a migraine, much less a headache, but when I finally did get up I knew something wasn't right.

It was 6 a.m. and I was in the shower getting ready to go to work. I remember feeling just awful, as if I were going to faint. My husband, Duane, was out of town, so I couldn't ask him for help, and he wasn't there to see if I was acting strangely. When I got out of the shower all I could think about was how tired I was and that I wanted to go back to bed. I just thought that I needed more sleep because I had worked late at the office the night before. 

I called my secretary, Cissie, and told her how I was feeling. She said that I had left her a few notes the night before and she mentioned that they were a bit incoherent (this didn't really surprise me because frequently my notes can be incoherent). Cissie told me that I needed to get some more sleep and that she would take care of everything, so I dried my hair and went back to bed.

When I woke up again it was 9 a.m. and I knew I needed to get to the office. I drove myself to the office because I still thought that I just had the flu or something. To this day I don't remember making that drive. Thank goodness I made it there without getting into an accident.

I arrived at the office around 10 a.m. When Cissie saw me, she knew immediately that something was wrong. At the time, Cissie had been working with me for about four years so she knew me quite well. I was supposed to have lunch with my friend, Beth, that day and she had already called to confirm our lunch. Cissie knew Beth, and when she called, Cissie had explained to her what was going on with me. Cissie had already asked Beth to come over early because she just had an instinct that something was seriously wrong. 

Beth immediately came to pick me up. She took me to the emergency room at the hospital that was fortunately just a few blocks away. Once I was in the emergency room, everything became a blur! Later, I was told that I underwent a series of tests, including a CT scan and an MRI. After many tests and lots of questions, the doctors determined that I had an abnormality on the left side of my brain. I was admitted to the hospital and was started on anti-seizure medication. The doctors were concerned that I may have had a mild seizure the night before, and they wanted to prevent a possible recurrence. I remember Beth told me that she had called my husband to tell him what had happened to me. Then she told me to just go back to sleep, which is what I did for most of the day.

Duane was away on a motorcycle trip, but he was only about 5 hours away. Beth told him that I had been admitted to the hospital and that the doctors had found "something on my brain." She told him to get to the hospital as quickly as possible. When he got to the hospital he collapsed at my bedside in tears, terrified that he would never see me the way that I was BEFORE he went out of town. He later told me that he thought I had suffered a stroke. He was so afraid that he would find me lying in bed unable to speak. He also told me that the motorcycle ride to the hospital was the longest 5 hours of his life. 

Later that day, the doctors told us that the tests had revealed a mass in the left frontal lobe. It appeared to be a "glial-type" brain tumor. However, they indicated that the tumor was located in an area of my brain where it could be surgically removed.

At this point, it was time to let my family know what had happened to me over the last several hours. Unfortunately, that task was left to my husband, Duane. He immediately called my parents in Knoxville, Tennessee. Although this was extremely shocking news, my father, a retired orthopedic surgeon, and my mother, a former Navy nurse, understood exactly what they had been told. My parents then informed the rest of my family (three older brothers and one older sister), all of whom live in Knoxville, Tennessee. I'm the youngest of five children and I live 1,000 miles away from the rest of the family. I can imagine how difficult it must have been for them. 

I was kept in the hospital for a few days. Then I was allowed to go home to "enjoy" the 4th of July weekend. I returned to the hospital the morning of July 6th so that my neurosurgeon could remove the mass in my brain. For the week or so between diagnosis and surgery, I really don't remember too many details. I was probably in some state of shock; however, when my neurosurgeon told me that I had a brain tumor, the reality set in. That was when it became very clear to me that the world as I had known it had changed forever, and my journey of living with a brain tumor began.

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Copyright © 2003 by Jones and Bartlett Publishers, Inc.

All rights reserved. No part of the material protected by this copyright notice may be reproduced or utilized in any form, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission from the copyright owner.