Brain tumors still rare; cellphone link is unproven
Senator Edward M. Kennedy's recent diagnosis with malignant glioma, a rare brain cancer that is usually rapidly fatal, is renewing questions about whether brain cancer is on the rise - and whether cellphones have anything to do with it.
The number of people with the disease is essentially holding steady, doctors say, but the diagnosis of Kennedy and other famous individuals such as attorney Johnnie Cochran, who died from a glioma in 2005, may give the impression of a rapid rise.
There has been a slight increase compared with 30 years ago, largely due to better diagnostic tools, epidemiologists say, and the fact that brain cancer risk increases with age, and Americans are growing older. The risk of using cellphones remains controversial.
"We've had amazing new technologies, starting in the early 1980s with computerized tomography and in the late '80s and '90s the MRI," said Dr. Otis Brawley, chief medical officer of the American Cancer Society. "All of a sudden we started looking and found more and more tumors."
According to the American Cancer Society, the incidence of brain cancer - the number of cases per 100,000 people - rose from 6 in 1975 to 7 in 1985, and then declined to 6.5 in 2005.
In 2008, the cancer society expects more than 20,000 individuals to be diagnosed with all forms of brain tumors, and approximately 13,000 people will die from it. Glioblastoma, the deadliest form of brain cancer, is by far the most common type, and the incidence rate shoots up at age 65, according to the Central Brain Tumor Registry of the United States. Incidence is substantially higher for whites than for any other group, and men fare worse than women in all racial and ethnic groups, though researchers don't know why.
"The sad part of it all - I've been studying brain tumors my whole career - [is] the numbers are so small, it's really difficult for any one center to be able to conduct a research study that's going to be conclusive" about causes or treatments, said Melissa Bondy, a professor of epidemiology at M.D. Anderson Cancer Center in Houston and a member of the Brain Tumor Epidemiology Consortium, a large group of researchers planning to pool data and conduct genetic studies.
Brain tumors are an "orphan disease" because of the small numbers, with limited funding for research, she said.
Studies of brain tumors in families suggest a genetic susceptibility to gliomas, though the genetic causes have yet to be clarified, according to the brain tumor consortium.
People exposed to high-dose radiation and possibly high-dose chemotherapy, such as treatment for childhood cancers, are one of the few established environmental causes of glioma, and genetic factors may determine the degree of risk from these exposures, according to the consortium. A study of Israeli children who underwent radiation for a scalp condition showed an association between ionizing radiation and brain tumors. A high incidence of meningioma, a slow-growing tumor, was shown for atomic bomb survivors in Nagasaki and Hiroshima.
Dental X-rays, electromagnetic fields, herpes viruses, and a virus called SV40, carried by monkeys, are all potential causes under investigation. One study showed allergies and asthma may protect against tumors.
The association between cellphone use and malignant brain tumors remains unclear, Bondy said. A Danish study published two years ago in the Journal of the National Cancer Institute followed 420,095 cellphone users for 20 years and found no connection.
However, a new meta-analysis - a study grouping the results of several studies together - published this month in the International Journal of Oncology did find a connection between heavy mobile phone use and gliomas, as well as acoustic neuroma, a type of benign tumor that can lead to hearing loss. Meta analyses can be flawed, because they pool studies of varying design and quality.
Results from INTERPHONE, another research project, coordinated by the International Agency for Research on Cancer, will combine investigations from 13 European Union countries. So far, country-specific results have been mixed.
"I think it's very questionable that cellphones are causing brain tumors," Bondy said. "Don't you think by now, if there is such a risk, we'd start to see an increase?"
