Study Links Smoking to Increased Risk of Breast Cancer

Smoking can cause a significant increased risk of breast cancer, especially in women who started smoking during adolescence or who have a family history of the disease, according to a new study.

While there are known risks of tobacco smoke, there is limited conclusive evidence of its effect on the risk of breast cancer; plausible biological reasons exist, but epidemiological evidence is inconsistent, the researchers noted.

“Authors of more recent epidemiological analyses have reported modest raised risks with current or former smoking, but questions remain about the extent to which this association is a consequence confounded by alcohol use, whether risk is increased if smoking starts in adolescence or before first childbirth, and whether risk is modified by family history of breast cancer,” wrote the authors of the study.

The study, published in Breast Cancer Research, included 102,927 women from the Generations Study, a cohort study consisting of over 113,700 women age 16 years or older from the United Kingdom. The participants, recruited from 2003-2013, completed questionnaires that inquired about smoking regularity, age started and stopped, and the number of cigarette smoked per day throughout different periods in their lives.

Results of the study showed that women who had ever smoked were 14% more likely to develop breast cancer than those who had never smoked. In particular, women who started smoking before age 17 had a significant increased risk of developing breast cancer: those who began smoking before age 17 had a 24% increased risk, while those who started smoking between ages 17 and 19 had 15% increased rate.

In regard to smoking duration, the authors found that smoking for more than 10 years increased the risk of developing breast cancer by 21%, with a small increase for those who smoked for more than 30 years (22%).

Of the women who had quit smoking, there was still a 28% increased risk of developing breast cancer for those who had quit for less than 10 years. For those who quit for 10 to 19 years, there was a 21% increased risk, and those who quit for more than 30 years had a 10% increased risk.

The authors also found that the association between smoking and breast cancer was significantly larger among women who had a family history of the disease. For women with a family history of breast cancer, hazard ratios were raised if smoking started both after age 20 (56%) or before age 20 (26%), and if started more than 5 years after their first menstruation (53%).

“We found that smoking was associated with a modest but significantly increased risk of breast cancer, particularly among those who started at adolescent or pre-menarcheal ages, and that the relative risk of breast cancer associated with smoking was significantly greater for women with a family history of the disease,” concluded the authors.