Does smoking raise risk of breast cancer? - Boston Globe (blog)

The study, published Monday in the Archives of Internal Medicine, found that smoking, whether currently or in the past, only increased lifetime breast cancer risk by about 6 percent. That's pretty small considering that smoking increases lung cancer risk by 1,000 to 2,000 percent or that daily vigorous exercise reduces breast cancer risk by about 30 percent.

Even the researchers, who are affiliated with the Harvard School of Public Health, say the potential effect of smoking on breast cancer risk is "modest." Strangely, exposure to passive smoke didn't increase breast cancer risk, despite other findings showing that it increases other health risks.

And the researchers also found that while smoking appeared to raise the risk of breast cancer in young women, it seemed to have a small protective effect in postmenopausal women -- too small to even be considered statistically significant.

Of course, this small protection, if it wasn't due to random chance, is vastly outweighed by the certain health risks caused by smoking. So, no, postmenopausal women should not take up smoking or think it's okay to continue for its dubious protective effects against breast cancer.

I asked a statistician what she thought of the study and she told me the finding was "marginal" and not big enough to make any sort of impact on clinical practice. (She preferred to remain anonymous since she works at the Harvard School of Public Health.) For example, doctors probably aren't noticing an uptick in breast cancer diagnoses among their patients who smoke like they do with lung cancer diagnoses. And women smokers don't need to get more frequent breast cancer screenings.

Also, it's important to keep in mind that this finding was from an epidemiological study -- the well known and highly respected Harvard Nurses' Health study, which has followed more than 100,000 nurses for three decades. That means other factors could have confounded the results. Smokers may lead vastly different lives than nonsmokers, so perhaps something else in their lifestyle could have been responsible for the small increase in breast cancer. While the researchers were able to account for certain factors like family history of breast cancer, alcohol consumption, and birth control pill use, they couldn't account for all factors, including exercise and diet.