Women taking the next puff of a cigarette might consider this: smoking 100 or more cigarettes may substantially increase their odds of developing breast cancer, researchers report.

Previous studies linked regular exercise, limiting alcohol intake, and avoiding postmenopausal obesity as lifestyle changes that can reduce women’s odds of developing breast cancer, notes Dr. Ivana T. Croghan and colleagues in The Breast Journal.

The current study provides new evidence that “a woman smoker can reduce her risk of breast cancer by stopping smoking as soon as possible,” Croghan commented to Reuters Health via email.

Croghan’s group compared smoking history and other breast cancer risk factors among 1,225 women who developed breast cancer and 6,872 who did not during the first year after their initial visit to the Mayo Clinic Breast Clinic.

Surveys completed during this visit indicated just over 10 percent were current smokers, almost 9 percent were former smokers, and 81 percent had never smoked, Croghan, with the Mayo Clinic Nicotine Research Program in Rochester, Minnesota, and associates report.

In addition to the link with smoking, women who had used oral contraceptives for 11 years or longer had a whopping 200 percent increase in the odds of developing breast cancer. Women who used postmenopausal hormone therapy showed 81 percent increased odds, while aging raised the odds of developing breast cancer by 2 percent per year.

On the flip side, Croghan and colleagues report that having a hysterectomy decreased women’s odds by 35 percent. Also, they did not see a compounding increase in risk for breast cancer among women with more than one risk factor.

Croghan noted that prior investigations with contradictory results regarding smoking and breast cancer risk did not consistently define smoking as current, former or never. The current study defines anyone who ever smoked more than 100 cigarettes at any time as having a history of smoking. Those who smoked less were considered never-smokers.

Croghan’s group suggests further investigations using similar smoking definitions to assess how pre- and post-menopausal duration of smoking, amount smoked, and exposures to second-hand smoke might alter a woman’s odds of developing breast cancer.

SOURCE: The Breast Journal, September/October 2009