Tobacco Info

From Tobacco Info No. 5 - April 2011
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Both active and passive smoking cause breast cancer

Studies on the potential link between smoking and breast cancer have arrived at varied conclusions in the past. In addition, they were few in number and, in most cases, out of date.

New research published in January adds more evidence that smoking is a cause of breast cancer.  The study entitled Cigarette Smoking and the Incidence of Breast Cancer, published in the Archives of Internal Medicine, followed 111,140 nurses from 1976 to 2006 for active smoking. Authors Xue, Willett et al. found that smoking, especially smoking before the first birth, may be associated with a modest increase in the risk of breast cancer.

These results are further confirmation of the findings of an expert panel convened by four Canadian agencies, the Public Health Agency of Canada, the Ontario Tobacco Research Unit, Physicians for a Smoke-Free Canada (PSC) and the Canadian Partnership Against Cancer, to comprehensively examine the weight of evidence from epidemiological and toxicological studies and understanding of biological mechanisms with regard to the relationship between tobacco smoke and breast cancer. They found that active smoking and exposure to second-hand smoke (SHS) increase the risk of breast cancer.

Authors Johnson, Miller, Collishaw et al. concluded that “the association between active smoking and breast cancer is consistent with causality. Furthermore, the association between SHS and breast cancer among younger, primarily premenopausal women who have never smoked is consistent with causality. There are 20 known or suspected mammary carcinogens in tobacco smoke and recognized biological mechanisms that explain how exposure to these carcinogens could lead to breast cancer.”

An article entitled Active smoking and second-hand smoke increase breast cancer risk: the report of the Canadian Expert Panel on Tobacco Smoke and Breast Cancer summarized the panel’s 75-page report. The article was published by the journal Tobacco Control in January, 2010. The full report is available on the Ontario Tobacco Research Unit’s website.

Study findings

The mandate of the 11-member panel, made up of six Canadian experts and five from the US, was to provide an up-to-date synthesis of current knowledge and studies on exposure to tobacco smoke and breast cancer. The panel focused on the extensive research in the area, as well as examining active smoking and exposure to SHS and the association of these factors with premenopausal breast cancer.

The researchers found that smoking increases the risk of breast cancer in all women, with an average 50 to 70% increase in risk, depending on how much women smoke. Furthermore, exposure to second-hand smoke increases the risk of breast cancer in younger, primarily premenopausal women, by 40 to 50%.

“Even moderate exposure to passive smoking, such as living or working with a smoker early in life, increases a woman’s risk of breast cancer when she is in her 30s, 40s and 50s,” said panellist and University of Toronto public health expert Dr. Anthony Miller.

In addition, the panel claims that one in seven women in Canada will develop breast cancer in their lifetime and that one in five will develop the disease if they are an active smoker.

“An estimated 80 to 90% of women have been exposed to tobacco smoke in adolescence and adulthood,” said panel chairman Neil Collishaw of Physicians for a Smoke-Free Canada. “Those women face an increased risk of breast cancer because of that exposure.”


The panel made a number of recommendations and observations as a result of their findings. The first is that more research is needed in order to consolidate and amalgamate the available knowledge of the relationship between breast cancer and tobacco smoke.

The second is that there is a need for a more comprehensive health communication strategy, in particular for younger women. “A call for more education, communication and increased public awareness about the dangers of tobacco are key features of the WHO Framework Convention on Tobacco Control,” wrote the authors.

Furthermore, in light of these findings, Collishaw urged Canadian Health Minister Leona Aglukkaq to “consider including warnings on the risks of exposure to tobacco smoke for breast cancer... when the next set of revised warnings is publicly proposed” in a letter to the minister back in April 2009.  No warning on breast cancer is among those recently proposed by the government (January 2011), but breast cancer may be included as a topic for health warnings in the future.

“The most effective way of providing this information to every smoker is to make sure it is printed on every brand of cigarettes,” said Dr. Atul Kapur, PSC’s president. “Tobacco package warnings are highly effective because they are low-cost and high reach. Package warnings are delivered to smokers on virtually every occasion that the product is used.”

By Joe Strizzi