1. ¹Cancer Research UK Epidemiology Unit, Richard Doll Building, University of Oxford, Old Road Campus, Headington, Oxford OX3 7LF, UK
2. ²Department of Preventive Medicine, Norris Comprehensive Cancer Center, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA
3. ³Department of Health, E Floor, Government Office for the East Midlands, The Belgrave Centre, Stanley Place, Talbot Street, Nottingham, NG1 5GG, UK
4. ⁴Nuffield Department of Obstetrics and Gynaecology, University of Oxford, Womens Centre, Level 3, John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
5. ⁵Cancer Research UK Section of Epidemiology, Brookes Lawley Building, Institute of Cancer Research, Sutton, Surrey SM2 5NG, UK
6. ⁶Department of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK
7. ⁷Unit of Health Care Epidemiology, Department of Public Health, Old Road Campus, Headington, Oxford OX3 7LF, UK

Correspondence: Dr AW Roddam, E-mail: andrew.roddam@ceu.ox.ac.uk

Received 12 March 2007; Revised 24 May 2007; Accepted 25 May 2007; Published online 19 June 2007.

Abstract

Active smoking has little or no effect on breast cancer risk but some investigators have suggested that passive smoking and its interaction with active smoking may be associated with an increased risk. In a population based case–control study of breast cancer in women aged 36–45 years at diagnosis, information on active smoking, passive smoking in the home, and other factors, was collected at interview from 639 cases and 640 controls. Women were categorised jointly by their active and passive smoking exposure. Among never smoking controls, women who also reported no passive smoking exposure were significantly more likely to be nulliparous and to be recent users of oral contraceptives. Among those never exposed to passive smoking, there was no significant association between active smoking and breast cancer, relative risk (RR) of 1.12 (95% confidence interval (CI) 0.72–1.73) for past smokers and RR of 1.19 (95% CI 0.72–1.95) for current smokers, nor was there an association with age started, duration or intensity of active smoking. Compared with women who were never active nor passive smokers, there was no significant association between passive smoking in the home and breast cancer risk in never smokers, RR of 0.89 (95% CI 0.64–1.25), in past smokers, RR of 1.09 (95% CI 0.75–1.56), or in current smokers, RR of 0.93 (95% CI 0.67–1.30). There was no trend with increasing duration of passive smoking and there was no heterogeneity among any of the subgroups examined. In this study, there was no evidence of an association between either active smoking or passive smoking in the home and risk of breast cancer.