More than 18,000 brain and spinal cord tumors will be diagnosed in the United States this year. Yet little is known about what causes brain cancer; the only established risk factor is radiation, according to the American Cancer Society.
"If we are able to help explain the cause of even 1 or 2 percent of the total number of cases, that's important," said van Wijngaarden, an assistant professor and epidemiologist in the Department of Community and Preventive Medicine at the University of Rochester.
Published in the Sept. 1, 2006, issue of the International Journal of Cancer, the study computed the risk estimates for lead exposure and brain cancer from a census sample of 317,968 people who reported their occupations between 1979 and 1981. Van Wijngaarden was looking for evidence of an exposure-response trend, or a rise in cancer incidence or mortality associated with an exposure to a toxic substance. The goal among researchers who do this type of investigation is to identify preventable, environmental risk factors that might cause the gene mutations that lead to cancer.
Each occupation was classified into categories established by the National Cancer Institute. The NCI job matrix for lead is designed to estimate the likelihood of exposure and the intensity of exposure. It rates each occupation on a scale from zero (no exposure) to three (high exposure).
Gas station attendants from the 1970s and early 1980s, for example, were estimated to have a high probability of exposure, but only medium intensity of exposure because their direct contact with leaded gasoline was not as great as the potential for contact. The jobs with the highest probability and intensity of lead exposure were painters and automobile mechanics. But firefighters, engineers, automobile assemblers, truck drivers, plumbers, welders, and printers or typesetters were all among those individuals with some likelihood of lead exposure, according to the NCI matrix.
When Van Wijngaarden applied the matrix to nearly 318,000 people and followed their cancer rates for nine years, he found 119 brain cancer deaths. The death rate among people with jobs that potentially exposed them to lead was 50 percent higher than unexposed people, and the number of deaths was larger than in many previous studies, van Wijngaarden said. Other trends that emerged were slightly higher death rates among less educated and married individuals.
Scientists have suspected for years that lead is a carcinogen, which passes through the blood-brain barrier, making the brain especially sensitive to the toxic effects of lead. Van Wijngaarden is continuing his research with a pilot study to measure the actual bone-lead levels in people who have been diagnosed with brain tumors.
"My interest is in exploring the long-term implications of lead exposure," van Wijngaarden said. "Lately, a lot of the information about lead and its toxicity has focused on children. We do know that in young people it can cause acute illness and behavioral problems. But what is under appreciated, I believe, are the chronic health effects."