Jan. 6, 2004 -- A new study indicates that active smoking may play a much larger role in increasing breast cancer risk than previously thought.
The research shows women who smoke have a much higher risk of developing breast cancer compared with women who have never smoked.
Researchers say tobacco smoke contains a number of known carcinogens (cancer-causing agents), and by-products of cigarette smoke have been found in the breast fluid of smokers. But studies on the link between breast cancer and smoking have produced inconsistent results because they did not separate the effects of contributing factors such as passive or secondhand smoke exposure, age of breast cancer diagnosis, family history of breast cancer, and if the woman was a smoker at the time she was diagnosed with breast cancer.
Smoking Raises Breast Cancer Risk
In the study, published in the Jan. 7 issue of the Journal of the National Cancer Institute, researchers looked at breast cancer risk among 116,544 women in the California Teachers Study who reported their smoking status.
Between 1996 and 2000, 2,000 of the women developed breast cancer. The prevalence of breast cancer among current smokers was 30% higher than the women who had never smoked -- regardless of whether the nonsmokers had been exposed to secondhand or passive smoke.
In fact, breast cancer risks among people who never smoked that reported exposure to secondhand in the household were not greater than those found among never smokers without such exposure.
Among current smokers, the risk of breast cancer was significantly higher among those who started smoking before age 20, who began smoking at least five years before their first full-term pregnancy, and who had smoked for longer periods of time or smoked 20 or more cigarettes per day.
Current smoking was associated with a higher risk of breast cancer among women with no family history of breast cancer, but not among those with a family history of the disease.
Researchers say their results indicate that active smoking may play an important role in increasing the risk of breast cancer and merit further research into the connection.