Previously, the International Agency for Research on Cancer's 2002 Monograph on Tobacco Smoke and Involuntary Smoking found that there was no conclusive evidence linking second-hand smoke to breast cancer. However, the California Environmental Protection Agency has since released their December 2003 report, entitled Proposed Identification of Environmental Tobacco Smoke as a Toxic Air Contaminant which clearly identifies a causal association between second-hand smoke exposure and breast cancer in humans.
"Epidemiological studies, supported by animal data, provide evidence consistent with a causal association between ETS exposure and breast cancer in humans, which appears stronger for pre-menopausal breast cancer. Studies assessing the association between passive smoking and breast cancer have generally reported a positive, and often statistically significant association." (CALEPA Report, December 2003)
Below are individual studies which argue in favour of a link between passive smoke exposure and breast cancer:
Active and passive smokeing and risk of breast cancer by age 50 among German women. Kropp, S, Chang-Claude, J. Am J Epidemiol 1 Oct 2002; 156(7): 616-26.
Carcinogenic and endocrine disrupting effects of cigarette smoke and risk of breast cancer. Band, Pierre R., et al. The Lancet. 5 October 2002; 360: 1044-1049.
Smoking and early pregnancy increases breast cancer risk. Mayor, Susan. British Medical Journal. 12 October 2002. 325: 793.
Passive and active smoking and breast cancer risk in Canada, 1994-97. Johnson KC, et al. Cancer Causes and Control. March 2000; 11(3): 211-221.
Passive Smoking exposure and female breast cancer mortality. Wartenberg D, et al. Journal of the National Cancer Institute. 2000; 92(20): 1666-1673.
Active and passive cigarette smoking and the occurrence of breast cancer. Lash, TL and Aschengrau A. American Journal of Epidemiology. 1 January 1999; 149(1); 5-12.
Relation of breast cancer with passive and active exposure to tobacco smoke. Morabia A. American Journal of Epidemiology. 1 May 1996; 143(9): 918-928
Alcohol, smoking, passive smoking and caffeine in relation to breast cancer risk in young women. Smith SJ, Deacon JM and Chilvers CE. British Journal of Cancer. 1994; 70: 112-119.