Although smoking cigarettes has been linked to a variety of chronic health problems — including heart disease, stroke and several types of cancer — health experts have found no relationship between a woman's status as a smoker and her breast cancer risk. Over the past 40 years, dozens of studies, large and small, have found no indication that smoking cigarettes either increases or decreases the likelihood of a woman developing breast cancer.
Why this is the case is not clear. When researchers look at the relationship between smoking and other cancers, the results are dramatic: Smoking has been highly correlated to lung cancer risk, for example. Cigarettes contain many known carcinogens, and the chemical byproducts of smoking have been found in breast tissue and breast milk. So why is there no apparent connection with breast cancer?
Researchers theorize that smoking might equally increase and decrease risk because smoking acts against the production of estrogen, a hormone that plays a leading role in breast cancer. Women who smoke also are less likely to have endometrial cancer, which is related to estrogen, and tend to start menopause earlier. In theory, the anti-estrogenic effects of smoking could counter the cancer-causing effects of some of the chemicals in cigarettes.
The Surgeon General's Report in 2006 on exposure to secondhand smoke acknowledged that there is no evidence that smoking or secondhand smoke cause breast cancer but emphasized that women should not smoke because of all the other cancers and negative health outcomes that have been linked to smoking.
Despite the overall lack of data connecting smoking behavior and breast cancer, there are some small groups of women for whom cigarette smoking or exposure to secondhand smoke might increase breast cancer risk:
- Women who started smoking in their teens and who have smoked for more than 20 years might be at increased risk for breast cancer when compared with women who have smoked less than 100 cigarettes in their lifetime, according to data from the Erie County Smoking Study, reported in the January/February 2002 issue of Chemical Health and Safety. Though a handful of studies have supported this conclusion, other studies using data from large populations have not found an increased risk of breast cancer among lifetime smokers when compared with nonsmokers.
- Nonsmoking women who married young (before age 17) to men who smoked have an increased risk of a breast cancer diagnosis.
- Women who smoke and whose immediate female relatives have had three or more diagnoses of breast cancer or ovarian cancer among them are at increased risk for a breast cancer diagnosis.