Researchers from the Mayo Clinic have reported that women who have smoked 100 or more cigarettes in their life have a significantly increased risk of developing breast cancer. The details of this study were published in the September-October 2009 issue of The Breast Journal.
Although both active and passive smoking are known to increase the risk of lung cancer, findings for breast cancer have been mixed. A recent review of published studies suggests that both active and passive smoking may increase the risk of breast cancer—particularly premenopausal breast cancer. The following observations were made from this review of 19 studies:
Passive smoking increased the risk of breast cancer by 27%.
Among premenopausal women, passive smoking increased risk of breast cancer by 68%.
Active smoking increased the risk of breast cancer by 46%.
The Mayo Clinic’s study was a case control study that involved 1,225 women who developed breast cancer and 6,872 who did not in the first year after an initial visit to the Mayo Clinic Breast Clinic between 1993 and 2003. The women completed surveys regarding personal lifestyle habits and were considered smokers if they had smoked 100 or more cigarettes in their lifetime.
The results indicated that women who were former or current smokers had a 25% increased risk of developing breast cancer (P=0.004). They also found that hysterectomy was associated with a 43% reduction in risk of breast cancer. Oral contraceptives and exogenous hormones increased the risk of breast cancer by twofold.
Comments: This study confirms previous studies suggesting that smoking can play a major role in breast cancer etiology.
 Croghan IT, Pruthi S, Hays JT, et al. The role of smoking in breast cancer development: An analysis of a Mayo Clinic cohort. The Breast Journal. 2009; 15: 489-495.