BMC Cancer Research article Case-control study of tobacco smoke exposure and breast cancer risk in Delaware Dana E Rollison*1, Ross C Brownson2, H Leroy Hathcock3 and Craig J Newschaffer4,5 BioMed Central Open Access Address: 1Division of Cancer Prevention & Control, H Lee Moffitt Cancer Center & Research Institute; Tampa, FL, USA, 2Department of Community Health and Prevention Research Center, Saint Louis University School of Public Health, St Louis MO, USA, 3Delaware Division of Public Health, Dover, DE, USA, 4Department of Epidemiology and Biostatistics, Drexel University School of Public Health, Philadelphia, PA, USA and 5Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA Email: Dana E Rollison* - dana.rollison@moffitt.org; Ross C Brownson - brownson@slu.edu; H Leroy Hathcock - Leroy.Hathcock@state.de.us; Craig J Newschaffer - cnewscha@drexel.edu * Corresponding author Published: 2 June 2008 BMC Cancer 2008, 8:157 doi:10.1186/1471-2407-8-157 This article is available from: http://www.biomedcentral.com/1471-2407/8/157 Received: 5 December 2007 Accepted: 2 June 2008 © 2008 Rollison et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background: Tobacco smoke exposure may be associated with increased breast cancer risk, although the evidence supporting the association is inconclusive. We conducted a case-control study in Delaware, incorporating detailed exposure assessment for active and secondhand smoke at home and in the workplace. Methods: Primary invasive breast cancer cases diagnosed among female Delaware residents, ages 40–79, in 2000–2002 were identified through the Delaware cancer registry (n = 287). Delaware drivers license and Health Care Finance Administration records were used to select age frequency- matched controls for women <65 and ≥ 65, respectively. Detailed information on tobacco smoke exposure was obtained through telephone interviews. Results: A statistically significant increased risk of breast cancer was observed for ever having smoked cigarettes (odds ratio = 1.43, 95% confidence interval = 1.03–1.99). However, there was no evidence of a dose-response relationship between breast cancer risk and total years smoked, cigarettes per day, or pack-years. Neither residential nor workplace secondhand smoke exposure was associated with breast cancer. Recalculations of active smoking risks using a purely unexposed reference group of women who were not exposed to active or secondhand smoking did not indicate increased risks of breast cancer. Conclusion: These findings do not support an association between smoking and breast cancer. Background More than 180,000 cases of breast cancer are expected to be diagnosed in the U.S. in 2008 [1]. While several repro- ductive and genetic risk factors for breast cancer have been well established in the epidemiologic literature, these fac- tors account for less than half of all breast cancer and are not modifiable [2]. Exposure to tobacco smoke is a poten- tially modifiable factor that may be associated with increased breast cancer risk, although evidence supporting the association is inconclusive. Page 1 of 9 (page number not for citation purposes)