Cigarette smoking boosts breast cancer risk

A new study led by researchers at Harvard School of Public Health suggests that cigarette smoking can increase risk of breast cancer. 

The study, published recently in Archive of Internal Medicine, showed every increase of 20 pack-years before having first birth was associated with an 18 percent increased risk of breast cancer. 

Cigarette smoke is known to contain many carcinogens and has been considered to be a major disease for lung cancer.  But conversely, cigarette smoke also contains antiestrogenic substances which may potentially reduce the risk of breast cancer. 

The study led by Fei Xue MD, ScD and colleagues was intended to examine the association between smoking and breast cancer risk. 

For the study, the researchers looked at data from participants of the Nurses' Health Study and identified 8772 incident cases of invasive breast cancer during 3,005,863 person-years of follow-up. 

Women who ever smoked were 6 percent more likely than those who never smoked to be diagnosed with breast cancer, Xue et al found after they adjusted their analysis for potential confounders.  The increased risk was statistically significant. 

At higher risk for breast cancer were women those who had been a heavy smoker currently or in the past, those who started smoking at younger ages, those who smoked for a long period, and those who had more pack-years of smoking. 

Twenty pack-years of premenopausal smoking was correlated with a 11 percent increased risk of breast cancer compared with those who never smoked and 20 pack-years of smoking prior to having first birth was associated with a 18 percent increased risk. 

However, there was not increased risk associated with postmenopausal smoking and exposure to passive smoking did not seem to increase breast cancer.

The researchers concluded "Active smoking, especially smoking before the first birth, may be associated with a modest increase in the risk of BC (breast cancer)." 

Breast cancer is expected in one in seven American women in their lifetime.  Each year, more than 175,000 women are diagnosed with the disease in the U.S. and about 50,000 die because of the disease, according to the National Cancer Institute.

David Liu, Ph.D. and editing by Denise Reynolds