Smoking or inhaling secondhand smoke can increase the risk of breast cancer, according to a large study, published in the current number of Causes and control [cancer. The work may help explain why previous studies of the link between smoking and breast cancer has come up with conflicting results.
Researchers have long puzzled over the blurred relationship between cigarettes and breast cancer. Some studies have suggested that smoking may actually protect women, a finding the researchers attributed to the removal of nicotine from estrogen, often linked to breast cancer hormone. But most follow-up studies found no relationship between smoking and breast cancer; and others have shown that smoking and secondhand smoke in particular, increased the risk.
Kenneth Johnson and colleagues at the Laboratory of the Canadian government for Disease Control in Ottawa glean information on 2317 women with breast cancer and 2438 healthy women from a Canadian study monitoring Cancer. Participants answered questions about risk factors such as alcohol consumption, physical activity and age at menarche, and their lifetime exposure to tobacco smoke at home and at work. For premenopausal women, smoking or regular exposure to secondhand smoke doubled the risk of breast cancer; for postmenopausal women, these factors have increased the risk of 50% and 30% respectively
Johnson said the study may explain why studies consistently show that secondhand smoke increases the risk of breast cancer -. his is the seventh to do - while others that examined smokers have had mixed results. Maybe, he says, it is because smoking and passive smoking are almost the same risk. Most previous studies have compared active smokers to people who had never smoked; but most women in the latter group were exposed to passive smoke "so that you are really exposed to compare exposed," Johnson said. In fact, when smokers in the new study were compared to all non-smoking - regardless of whether they were exposed to secondhand smoke or not - the risk of breast cancer was equal, as in studies previous. The results suggest that some women develop breast cancer when they were exposed to a certain amount of smoke, Johnson said - no matter how it gets into their bodies
Support for this theory came in 1996, when Christine. Ambrosone, biologist at the National Center for Toxicological Research in Jefferson, Arkansas, reported that women with a slow form of an enzyme that metabolizes carcinogenic tobacco had an increased risk of breast cancer. Ambrosone Johnson said the study is solid, but cautions that researchers still need to work on many details about the link between smoking and breast cancer. "My feeling is that breast cancer is a very heterogeneous disease, so that this relationship will be complicated."
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