Active and passive cigarette smoking and the occurrence of breast cancer

Using a case-control design, the authors studied female residents of five M assachusetts towns between 1983 and 1986. The objective was to measure the associations between breast cancer occurrence and exposure to active and pa ssive cigarette smoke. Until recently, exposure to tobacco smoke has not be en thought to cause breast cancer. Novel perspectives on measuring the asso ciation of tobacco smoke with the occurrence of breast cancer and studies o f genetically susceptible populations argue for further investigation. In t his study, the authors found that ever-active smokers had an odds ratio of 2.0 (95 percent confidence interval (CI) 1.1-3.6) when compared with never- active, never-passive smokers. Women who smoked only before their first pre gnancy (odds ratio = 5.6, 95 percent CI 1.5-21) and women who quit smoking 5-15 years before their index year (odds ratio = 3.9, 95 percent CI 1.4-10) were at the highest risk. Passive-only smokers had an odds ratio of 2.0 (9 5 percent CI 1.1-3.7) when compared with never-active, never-passive smoker s. Among those women who were exposed to passive smoke before age 12 years, the odds ratios were 4.5 (95 percent CI 1.2-16) for passive-only smokers a nd 7.5 (95 percent CI 1.6-36) for ever-active smokers. Women who were first exposed to passive smoke after age 12 years had lower, although still elev ated, odds ratios. The pattern of associations between exposure to cigarett e smoke and the occurrence of breast cancer comports with a model of breast carcinogenesis.