Tobacco Smoke
CATEGORY: IARC known, NTP known, Endocrine disruptor
USED IN: Cigarette smoke, secondhand smoke
Tobacco smoke contains PAHs, which may explain a potential link between increased breast cancer risk and both active and passive smoking. Tobacco smoke contains hundreds of other chemicals (Cal-EPA, 2005), including three known human carcinogens (polonium-210, a radioactive element; benzene; and vinyl chloride), as well as toluene, 1,3-butadiene and the nitrosamine NNK, all of which are known to cause mammary tumors in animals. NNK is a tobacco-specific carcinogen that has been shown to increase tumor cell proliferation and carcinogenic transformation of healthy breast epithelial cells (Chen, 2007; Mei, 2003; Siriwardhana, 2008).
Researchers at Japan’s National Cancer Center recently reported the results of a study involving 21,000 women ages 40 to 59. They found that both active and passive smoking increase the risk of breast cancer in pre-menopausal women (Hanaoka, 2005).
A large study of California teachers revealed an increased risk of breast cancer among smokers, particularly those who began smoking during adolescence, who smoked at least five years before their first full-term pregnancy, or who were long-time or heavy smokers (Reynolds, 2004). Several earlier studies also suggest that women who begin smoking cigarettes as adolescents face increased risks of breast cancer (Band, 2002; Calle, 1994; Gram, 2005; Johnson, 2000; Marcus, 2000). Similarly, results from the Canadian National Breast Screening Study indicated that increased incidence of breast cancer was associated with longer duration of smoking, number of cigarettes per day smoked, cumulative exposure to cigarette smoke, and beginning smoking prior to a woman’s first full-term pregnancy (Cui, 2006).
Until recently, we had more evidence linking secondhand smoke than active smoking to breast cancer risk. Current evidence suggests that both exposures increase breast cancer risk by about the same amount, even though women who are exposed to secondhand smoke receive a much lower dose of carcinogens than do active smokers (Ambrosone, 1996; Morabia, 1996). One possible explanation for this is that smoking damages the ovaries, thereby lowering estrogen levels. Researchers hypothesize that the lower level of estrogen decreases breast cancer risk, while at the same time carcinogens in cigarette smoke increase a smoker’s risk of breast cancer. Women exposed to secondhand smoke, on the other hand, may not get a large enough dose of smoke to depress estrogen levels.
A 2007 report from the Air Resources Board of California’s Environmental Protection Agency concluded that regular exposure to secondhand smoke is “causally related to breast cancer diagnosed in younger, primarily pre-menopausal women, and the result is not likely explained by bias or confounding” (Miller, 2007). A recent overview of the scientific literature confirmed the conclusion that where effects of environmental tobacco smoke on breast cancer risk are found, it is only significant for pre-menopausal women with the disease (Lee, 2006).
In addition to the chemicals addressed in more detail above, there are scores of industrial chemicals, products of combustion, dyes and pharmaceutical chemicals that have been linked to the induction of mammary tumors in animal models (Rudel, 2007). Many of these are listed in the relevant tables in the section of this document titled “From Science to Action.”
