National Cancer Institute Brain Tumor Study in Adults

National Cancer Institute
Wednesday, 20 December 2000

In 1994, researchers at the National Cancer Institute (NCI) initiated a comprehensive study on the causes of brain tumors in adults. Because the causes of brain tumors are largely unknown, the scientists are evaluating a wide range of environmental, lifestyle, and genetic factors that may increase the risk for developing brain tumors. These include:

- Cellular phone use;

- Occupational exposures, such as solvents, pesticides, and electromagnetic fields (EMFs) from electrical machinery; Family history of cancer;

- Dietary factors, including processed meats, artificial sweeteners, and vitamin and mineral supplements;

- Medical history such as allergies, head trauma and radiation exposures;

- Reproductive history and hormone use;

- Use of hair dyes; and

- Possible susceptibility genes.

The results of the brain tumor study will be published in various scientific journals over the next few years. Because of intense public interest, the first publication addresses cell phone use and brain tumor risk. As additional publications appear in the literature, the findings will be summarized at the end of this fact sheet.

Background

Statistics

Each year about 17,000 people in the United States are diagnosed with primary brain cancers. Brain and other nervous system cancers, however, make up a small percentage of the new cases of cancer in the United States – between 1 percent to 2 percent. The five-year survival for brain and other nervous system cancers from 1989 to1996 was 30 percent; this means that 30 percent of brain cancer patients survive at least five years after their tumor is diagnosed. (The survival rate does not include people with benign tumors.)

The risk of developing brain cancer increases with age. The rate for people under age 65 is 4.6 for every 100,000 people in the United States compared to 19.1 for persons 65 and older.

Long-term Trends

From 1990 to 1997, the over-all, age-adjusted incidence rates for brain cancer decreased; from 6.5 cases to 5.9 cases for every 100,000 persons in the United States. The mortality rates from 1990 to 1997 have also decreased slightly; from 4.3 deaths to 4.1 for every 100,000 persons in the United States.

Looking at long-term trends for specific age groups, it appears that among persons 70 or older, there was a higher incidence of brain cancers in 1991 to 1995 compared to 1975 to1979. This is in contrast to persons under age 70, for whom the rates were similar in both periods. The most dramatic increase was in the 85 or older group, for which the rates in the most recent five-year period were nearly three times higher than those in 1975 to 1979 (15.7 cases vs. 5.4 cases per 100,000 persons in the United States). The higher rates probably are due, at least in part, to the improvements in the ability to diagnose and treat brain tumors in elderly patients. The increased use of CT (computed tomography), MRI (magnetic resonance imaging) and stereotactic biopsy procedures (more precise methods for locating and diagnosing tumors) correlates with the increased incidence trends, and represents a more recent widespread tendency of physicians to aggressively pursue brain diagnoses in older patients.

Types of Brain Tumors

Primary brain tumors are tumors that arise in the brain, unlike tumors that begin elsewhere in the body and then spread to the brain. They are classified by the type of cell in which they develop. The most common brain tumors are gliomas. Gliomas develop in the glial cells which make up the soft, spongy tissue that supports the nerve cells in the brain. There are several types of gliomas. One type, astrocytoma, arises from small, star-shaped cells called astrocytes, and can grow anywhere in the brain or spinal cord. In adults, astrocytomas most often arise in the cerebrum, the largest part of the brain that fills most of the upper skull. Glioblastoma is an especially malignant form of astrocytoma. Gliomas are more common among men. When people say "brain cancer," they usually are referring to glioma. "Brain tumor" is a more general term and includes benign as well as malignant tumors.

Meningiomas are brain tumors which develop in the meninges, the protective membrane covering the brain directly underneath the skull. These tumors are usually benign and grow slowly. They occur most often in women between 30 and 50 years old.

Schwannomas are benign tumors that develop in Schwann cells. Schwann cells produce the myelin that covers and protects the nerve cells outside the central nervous system.

Acoustic neuromas are a type of schwannoma that occurs in the nerve between the brain and the ear. They occur primarily in adults and affect women more often than men.

Among adults, the most frequent types of brain tumors are astrocytic tumors, meningiomas, acoustic neuromas, and pituitary gland tumors. Less common types include lymphomas, vascular tumors, and tumors of the pineal gland.

Risk Factors

There are only a few well-established risk factors for brain tumors. People receiving radiotherapy (high-dose ionizing radiation) to the head during childhood are at increased risk for developing brain tumors as are people with certain rare genetic disorders such as neurofibromatosis and Li-Fraumeni syndrome.

The risk associated with low doses of ionizing radiation is less clear; radiation from diagnostic X-rays probably carries minimal risk. (Ionizing radiation, either gamma or X-rays, is high frequency radiation and can cause the breaking of molecular bonds, damaging genetic material, DNA). The molecular and health effects in humans of lower frequency, non-ionizing radiation such as that produced by cell phones or power lines, are not clear.

There have been several epidemiologic reports suggesting that nervous system cancers may be related to a variety of environmental exposures. Among the exposures are certain chemicals known as N-nitroso compounds and electromagnetic fields (EMF) from low frequency non-ionizing radiation. To date, studies concerning N-nitroso compounds (e.g., nitrosamides or nitroasmines) and brain tumors in humans are highly inconsistent. Similarly, the available EMF data are insufficient to support the conclusion that EMF from low-frequency fields such as those associated with electrical appliances or electric power lines, causes cancer.

Epidemiology studies have suggested that brain cancer occurs more frequently among workers in certain industries:

- the manufacture of synthetic rubber and polyvinyl chloride;

- the refining of crude oil and the production of petroleum-based chemicals;

- the manufacture of pharmaceuticals

- farming.

In addition, certain professional groups such as chemists, embalmers, pathologists, and artists appear to have higher than expected brain cancer rates.

However, aside from the small percentage of brain tumor cases that can be linked to exposure to high-dose ionizing radiation to the head or certain inherited genetic alterations, few specific risk factors have been convincingly linked to brain tumors.

Patient Population

The NCI study of brain tumors in adults includes 782 brain tumor cases and 799 controls from three medical institutions: St. Joseph's Hospital and Medical Center in Phoenix; Brigham and Women's Hospital in Boston; and Western Pennsylvania Hospital in Pittsburgh. The controls are people who were admitted to the same hospitals as the brain tumor cases for treatment of a variety of non-cancerous conditions. Controls were matched with cases by hospital, sex, race, age and distance of residence from hospital. Data collection began in 1994 and was completed in 1998.

The study included brain cancer patients recently diagnosed with glioma (489 cases), meningioma (197 cases) or acoust 5ic neuroma (96 cases). Patients with tumors that originated in other parts of the body and then spread to the brain were not included. The study was restricted to adults who were age 18 or older who received care at one of the participating hospitals, resided within 50 miles of the hospital, and could understand English or Spanish.

Data Collection

Data were collected through computer-assisted patient interviews. A structured personal interview was done by a research nurse to obtain information about the use of portable telephones, occupational history, including workplace exposures to chemicals and electromagnetic fields, hobbies with potential for solvent exposures, personal and family medical history, reproductive history and hormonal exposures, and use of tobacco and hair coloring products. Education, marital status, place of birth, and household income information was also collected. If the patient had died or was too ill to conduct the interviews, the spouse or another close family member answered the questions.

In addition to the personal interview, a self-administered paper questionnaire covering diet, alcohol consumption, vitamin supplements, and home use of electrical appliances was completed by each participant or a close family member.

Blood samples were collected to explore a variety of questions related to possible inherited gene mutations or polymorphisms and sensitivity to agents that cause mutations, and to assay for biological markers that may reveal past environmental exposures.

Results/Publications

There was no evidence of higher brain tumor risk among people who use hand-held cellular phones compared to those who do not use them.

The risk of developing brain tumors did not increase with increasing years of use or average minutes of use per day, nor did brain tumors among cellular phone users tend to occur more often than expected on the side of the head on which people reported using their phone. There was no evidence that the risk of any of the three major categories of tumors included in the study (glioma, meningioma, or acoustic neuroma) was increased among persons who used cellular telephones 60 or more minutes per day, or regularly for up to five years. However, if an increased risk occurs only after five or more years, or only among very heavy users, this study would not have detected it. Also, the study was done when most cellular phones were analogue phones, whereas today most people use digital phones.

Reference: Inskip P.D., Tarone R.E., Hatch E.E., Wilcosky T.C., Shapiro W.R., Selker R.G., Fine H.A., Black P.M., Loeffler J.S., Linet M.S. Cellular telephone use and brain tumors. New England Journal of Medicine 2001; 344: 79-86.

For more information, or to contact National Cancer Institute, see their website at: www.cancer.gov