This summary table contains detailed information about research studies. Summary tables offer an informative look at the science behind many breast cancer guidelines and recommendations. However, they should be viewed with some caution. In order to read and interpret research tables successfully, it is important to understand some key concepts. Learn how to read a research table.
Introduction: Smoking increases the risk of many types of cancer (including cancers of the lung, kidney and pancreas). Although findings on a possible link to breast cancer remain mixed, there is growing evidence that smoking may slightly increase the risk of breast cancer. More research is needed before solid conclusions can be made about a potential link between smoking and breast cancer.
Some studies have shown smoking before a first childbirth may increase the risk of breast cancer [1-3]. Others have found no link between the two .
Find information on secondhand smoke exposure (also called passive smoking) and the risk of breast cancer.
Learn more about smoking and breast cancer risk.
Learn about the strengths and weaknesses of different types of studies.
See how this risk factor compares with other risk factors for breast cancer.
Read our perspective on smoking and breast cancer risk (November 2012).*
*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date at this time.
Study selection criteria: Prospective cohort studies with at least 200 breast cancer cases and meta-analyses. Table note: Relative risk above 1 indicates increased risk. Relative risk below 1 indicates decreased risk.
Study Population(number of participants)
Relative Risk of Breast Cancer in Current Smokers Compared to Never Smokers,RR (95% CI)
Prospective cohort studies
Nurses' Health Study 
Bjerkaas et al. 
NIH-AARP Diet and Health Study 
186,150 (7,841 cases)
Canadian National Breast Screening Study 
Cancer Prevention Study II (CPS-II) 
73,388 (3,721 cases)
Women’s Health Initiative Observational Study 
California Teachers Study 
Iowa Women's Health Study 
Norwegian-Swedish Cohort Study 
Nurses' Health Study II 
Ha et al. 
Norwegian study 
Japan Collaborative Cohort Study for Evaluation of Cancer Risk 
Collaborative Group on Hormonal Factors in Breast Cancer 
Gaudet et al. 
NS = No statistically significant increase or decrease in risk
† Most participants were premenopausal
‡ Estimated from person-years of follow-up time
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