Sep. 10, 1997 LAS VEGAS, Sept. 9 -- New research shows, for the first time under real-life conditions, evidence of a cancer-causing substance in non-smokers who work in smoke-filled rooms. That substance, called NNK, was biologically processed and its metabolite detected in their urine. The study is being presented here today at a national meeting of the American Chemical Society.
"This is the first time that a metabolite of a tobacco-specific lung carcinogen has been found in the urine of non-smokers exposed to environmental tobacco smoke under field conditions," says Dr. Stephen Hecht of the University of Minnesota Cancer Center.
NNK is an abbreviation for 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone. It is the only known lung carcinogen found solely in tobacco smoke and is formed from nicotine. According to Dr. Hecht, NNK is particularly efficient at inducing adenocarcinoma in animals, a cancer of the lung periphery common in smokers. Hecht also says, "Adenocarcinoma is the type of lung cancer that's most commonly found in non-smokers who are exposed to environmental tobacco smoke." Lung cancer is normally rare in non-smokers.
The nine subjects of this study were non-smoking hospital workers caring for live-in patients in the smoking area of a Canadian veterans hospital. Their urine samples were collected three times during one day at the end of a work week. The samples were then sent to Hecht's laboratory where they were analyzed using highly sensitive equipment custom-designed to detect a human by-product (metabolite) of NNK called NNAL-Gluc.
All nine test subjects had detectable NNAL-Gluc levels. The levels were about 70 times lower than those found in smokers. However, Hecht says no NNAL-Gluc could be found in control samples (water blanks and urine from laboratory personnel not known to have been exposed to cigarette smoke). He concludes, "I feel certain that in a much larger study you would see the same kind of results."
Though risk varies widely, any contact with a carcinogen creates some chance of getting cancer and Hecht says this study "provides a link between the assumption that a person is being exposed to carcinogens and the reality that they actually are." Curtis Harris, MD, chief of the Laboratory of Human Carcinogenesis at the National Cancer Institute adds, "It certainly gives an indication that a person's been exposed. That information will be useful in further epidemiological studies to confirm the link between environmental tobacco smoke and lung cancer."
In 1993, Dr. Hecht was co-author on a New England Journal of Medicine paper that detailed similar tests on five non-smokers experimentally exposed to environmental tobacco smoke from a smoking machine while enclosed in a small chamber. That test was the first demonstration that non-smokers could take up and metabolize NNK. However, smoke exposure under those conditions was about 2-3 times higher than in the present "real-life" study.
The laboratory method used in the current study was 20 times more sensitive than that used for the New England Journal of Medicine paper. Dr. Hecht hopes to now use the new method to study larger samples of non-smokers exposed to environmental tobacco smoke.
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