Although cigarette smoking and use of other tobacco products are considered to be the greatest single source of human exposure to certain carcinogens, they do not appear to cause brain cancer, a Yale investigation has found.
"Brain cancer incidence and mortality have been increasing in many industrialized countries," said Tongzhang Zheng, associate professor of epidemiology and environmental health at Yale School of Medicine and principal investigator of the study published in a recent issue of the journal Cancer Epidemiology, Biomarkers & Prevention. "Some have suggested that cigarette smoking and other tobacco product use may increase the risk of brain tumors because tobacco product use is considered to be the greatest source for human exposure to N-nitroso compounds, which are potent nervous system carcinogens in animal studies. Our investigation, however, did not find a positive association between cigarette smoking, or with use of other tobacco products, and risk of brain cancer."
Zheng said some studies have shown persons who smoked non-filtered cigarettes were at higher risk for brain cancer, but his investigation did not find an association. In addition, "there was no increased risk of brain cancer by various smoking characteristics, including age started smoking, years of smoking, number of cigarettes per day or life-time pack-years of smoking," he said.
The study, based on data from the state of Iowa, included 375 confirmed cases of glioma, and 2,434 population-based controls.
The aging, curing, fermentation and processing of tobacco and nicotine can give rise to carcinogenic N-nitroso compounds in tobacco products. Laboratory tests have shown ingestion of tobacco products causes brain tumors in mice.
"This is one of only a few studies to systematically examine the risk of a specific histological type of brain cancer, glioma, with use of particular types of tobacco products, including cigarettes, cigars or pipes, snuff and chewing tobacco, among both males and females," Zheng said. "Most of the earlier studies only compared smokers with those who never smoked, and lacked information on age smoking began, type of tobacco products used, duration or intensity of smoking. Very few studies have also reported the findings related to use of other tobacco products."
He said he did not know why ingestion of tobacco products would cause brain cancer in mice but not humans, but speculated that the human brain-blood barrier may limit the actual amount of N-nitroso compounds that reach the brain tissue.
Co-authors of the published findings were Kenneth Cantor of the National Cancer Institute; Yawei Zhang of the Department of Epidemiology and Public Health at Yale; Brian Chiu of the Department of Preventive and Societal Medicine at the University of Nebraska Medical Center, and Charles Lynch of the Department of Epidemiology at the University of Iowa College of Public Health.