A study appearing in the Archives of Internal Medicine links smoking before menopause, especially prior to giving birth, to a modest increase in the risk of developing breast cancer. The study, authored by Fei Xue, M.D., Sc.D., of Brigham and Woman’s Hospital and Harvard Medical School, Boston, found development of breast cancer was associated with a higher quantity of current and past smoking, smoking for a longer period of time, younger age at smoking initiation, and more pack-years (number of packs per day multiplied by number of years) of smoking. The researchers also saw evidence that smoking after menopause might be associated with a slightly decreased breast cancer risk. Exposure to passive smoking in childhood or adulthood was not associated with an increase in breast cancer risk.
As it turns out, Michael J. Thun, M.D. American Cancer Society vice president emeritus of Epidemiology, chaired a recent review effort put together by the International Agency for the Research of Cancer (IARC) on the issue of passive smoke and cancer. Here’s what he had to say.
“The small but consistent relationship with active smoking observed in the current study is consistent with the results from other cohort studies. In fact, preliminary results from the current study were known to members of a working group that reviewed this issue for the International Agency for the Control of Cancer (IARC) in October 2009. IARC classified the evidence that active smoking caused breast cancer as ‘limited,’ and concluded that the evidence for secondhand smoke could not be classified.
“The review by IARC is one of two by scientific consensus groups within the last three years that have reviewed the evidence regarding whether tobacco smoke (active and/or passive smoking) causes breast cancer. In addition to the IARC review, another report recently republished in Tobacco Control summarizes the conclusions of a group that met in Canada in November 2008. It concluded that the relationship between active smoking and both pre- and post-menopausal breast cancer is ‘consistent with causality,’ and also that the relationship between secondhand smoke and breast cancer in younger, primarily pre-menopausal women is ‘consistent with causality.’ This descriptor is from the language used by the California EPA Air Resources Board: the CalEPA term ‘consistent with causality’ means exactly the same thing as the IARC term: ‘Limited evidence.’
“It is appropriate to inform women that there is some evidence that tobacco smoke, both active and passive, may increase breast cancer risk, but this evidence remains inconclusive. What is certain is that tobacco smoke, whether inhaled by smokers or from secondhand smoke, has been proven to cause many harmful effects, including cancer, heart disease, and adverse reproductive effects, and that this evidence is incontrovertible. This is why the American Cancer Society helps to lead the fight to reduce exposure to tobacco smoke in the United States and globally.”
UPDATE 5:40 pm ET: Our colleague Dr. Len Lichtenfeld of the American Cancer Society weighs in with his response on Dr. Len’s Cancer Blog.