A BRAIN tumor has long been the most terrifying of malignancies, feared for its lethality and its position at the source of all thought and emotion. And now experts say the incidence of brain cancer may be on the rise.New studies of epidemiological data from this country and abroad indicate that the rise is especially dramatic among the elderly, but scientists say that even among the young, the rate of at least one rare form of brain cancer is surging.
Other studies suggest that certain jobs may predispose workers or their children to brain cancer, and some researchers believe electromagnetic fields from power lines and power stations can help promote the growth of brain tumors, although many experts fiercely dispute the theory.
Experts Are Concerned
”Wherever I go, people ask me whether there’s an increase in brain tumors,” said Dr. Paul L. Kornblith, chairman of the neurosurgery department at the Albert Einstein College of Medicine and Montefiore Medical Center in New York. ”And an awful lot of people in my field have the impression that there is a greater incidence than there was before. They are concerned about it.”
Scientists emphasize that there is by no means an epidemic of brain cancer. They say the incidence of brain cancer remains very low for the population as a whole, accounting for about 1.5 percent of all malignancies. For most age groups, the rate of the two most common and deadly brain tumors, the gliomas and the astrocytomas, has been relatively stable for at least 20 years.
Experts stress that trends in brain cancer are especially difficult to sort out, largely because the technology for diagnosing brain tumors has sharply improved over the last 15 years. With the aid of advanced imaging methods like CAT scans and magnetic resonance imaging, or MRI, doctors are now able to diagnose brain cancers that in the past might have mistakenly been described as strokes, senile dementia or other neurological disorders.
”If we agree that we are diagnosing a greater number of patients with brain tumors than before, a lot of that could be explained by the increased sensitivity of diagnostic tools,” said Dr. Edward H. Oldfield, chief of surgical neurology at the National Institute of Neurolgical Disorders and Stroke. ”When the CAT scan was introduced in the early 70’s there was a big jump in the detection of brain tumors, and the MRI has an even greater sensitivity for detecting small tumors.”
Studies Track Increase
Yet recent studies indicate that certain patterns in brain cancer trends cannot be dismissed as a result superior diagnosis.
In one study, a new analysis of data collected by the National Cancer Institute’s nationwide cancer surveillance program, researchers at the National Institute on Aging in Bethesda, Md., have determined that among people over the age of 75, the incidence of brain tumorsmore than doubled from 1968 to 1985, the last year for which statistics are available. For people over 80, the rate of increase was even more shocking, soaring by 300 percent to 400 percent over the 17-year period, or by as much as 23 percent a year. ”Better diagnosis can explain some of the rise,” said Dr. Stanley I. Rapoport, chief of the laboratory of neuroscience at the Institute and the main author of the new report, which is to be published in The Journal of the National Cancer Institute. ”But something else is going on as well. Brain cancer in the elderly deserves more attention.”
Further confirming the Rapoport results, scientists at the National Research Council in Washington, the Karolinska Institute in Stockholm and other institutions recently compared mortality figures from about 1968 to 1987 for the United States, Britain, Italy, France, West Germany and Japan. They found that among people 65 and older, deaths from brain tumors rose in all nations at up to 200 percent for the period.
”There’s a stunning increase in mortality” from brain tumors, said Dr. Devra Lee Davis, an author of the paper, which is to appear in the December issue of The American Journal of Industrial Medicine. ”It holds true for all countries, a very sharp increase in a relatively short period of time.”
Dr. Davis said the increases in the six countries have continued long after the introduction of better imaging technology, indicating that improved diagnosis alone cannot explain the persistent rise.
Another Possible Cause
Among all age groups, the rate of a rare type of tumor, central nervous system lymphoma, which accounts for less than 5 percent of brain malignancies, has climbed 300 percent in 10 years. Experts say some of the rise is a result of AIDS, which makes people more susceptible to the malignancy. But others speculate that Epstein-Barr virus, which is becoming increasingly prevalent in the general population, may also be a cause.
Beyond the risk of primary tumors originating in brain tissue, malignancies that have spread to the brain from elsewhere in the body are rising rapidly. ”The longer people are surviving from cancers of the breast, lungs and other organs, the more chance they have that some of their tumor cells will metastasize to the brain,” said Dr. William R. Shapiro, chairman of neurology at the Barrow Neurological Institute of St. Joseph’s Hospital in Phoenix. Doctors emphasize that even among the elderly, the risk of brain cancer is low, and that any rise in occurrence is modest compared, for example, with the steep climb in malignant melanoma and lung cancer among women.
But they say brain cancer merits attention as an especially virulent disease for which there often is no treatment. The most prevalent types of brain tumors grow rapidly, spreading tumorous fingers into surrounding tissue and often killing within a year of diagnosis.
”Brain cancer is an awful, depressing cancer,” said Nigel H. Greig of the National Institute on Aging, a co-author of the Rapoport paper. ”It has one of the worst prognoses of all cancers. It’s almost invariably fatal. It’s lagged behind other cancers in chemotherapy and treatment, and survival time has not improved.”
For that reason, experts say, it is worth trying to determine why brain cancer seems to be rising among older groups, and to eliminate whatever risk factors can be identified. Dr. Davis says that to understand why brain tumors are on the rise in the elderly, researchers must consider the past.
”You must look at those aspects of the world that changed 30 or 40 yers ago, because the latency period for brain cancer is that long,” she said.
Speculating on such aspects, she points out that several decades ago, many more people worked in industrial, blue-collar jobs than do now, and that factories are often full of hazardous chemicals, running the gamut of the periodic table. ”There’s no question that proportionally more people used to work in dirtier places,” she said.
The high proportion of factory workers may partly explain why brain tumors are now showing up in many industrial nations. Assuming the workplace is now cleaner than it was, Dr. Davis said, the incidence of brain cancer may begin to drop in the future. But she believes that other chemicals in the environment, like pesticides, will compensate for any improvements in the workplace.
Dr. Davis believes that poor diet may be part of the reason for the rise in brain cancer. In the past, she said, people tended to pickle their meats and fish with suspected carcinogens like nitrites, and they ate few fresh vegetables and fruits, which contain anti-oxidants and other compounds thought to act as anti-cancer agents. Other researchers note that in the past, doctors and dentists were more cavalier in using X-rays and other forms of high-energy, or ionizing, radiation, now known to mutate DNA and wreak destruction in cells.
A number of researchers are now investigating the possibility that even low-energy, or non-ionizing, radiation, may somehow promote the growth of brain tumors. They contend that electromagnetic fields from power lines, power stations and even common household appliances can be a health hazard. But many experts dispute those assertions. They say that, unlike ionizing radiation, which strips apart atoms and damages DNA, electricity is non-ionizing and is not thought to mutate genetic material. Nevertheless, some experts suggest electromagnetic fields could subtly increase the risk of cancer, particularly high-voltage currents and alternating currents generated by large power stations and substations.
Writing in a recent issue of The New Yorker, the journalist Paul Brodeur discussed an apparent cluster of brain tumors on a street in Guilford, Conn., near a power substation. In a report in May, the Environmental Protection Agency said that there was a possible link between cancer and low-level electromagnetic fields, but that there still was not enough evidence to conclude that the fields directly caused cancer. In one study, Dr. David A. Savitz, an epidemiologist at the School of Public Health at the University of North Carolina in Chapel Hill, and colleagues considered all cases of childhood cancer from 1976 to 1983 in the Denver area.
Samples Are Small
They concluded that children who live near power lines that expose them to powerful electromagnetic fields had a 50 percent greater chance of developing brain tumors than those who did not live near power lines. But they said the samples were small and other potential health hazards in the environments considered had not been ruled out. Many experts insist the studies are inconclusive and contradictory. ”People are being very much alarmed over something for which there is no real evidence whatsoever,” said Dr. Eleanor R. Adair of the John B. Pierce Laboratory at the Center for Research in Health and the Environment, an affiliate of Yale University. ”Electricity has been around for a long, long time, and people’s life expectancy has nearly doubled since the invention of the light bulb.”