To the Editor.
—The recently reported Nurses' Health Study found no evidence for a positive association between dietary fat intake and breast cancer incidence.1 This study may not refute the hypothesis, however. A possible confounding factor is cigarette smoking. Approximately 22% to 25% of nurses smoke.2 Smoking may decrease the risk for breast cancer development, an observation of some, but not all, studies.3 Smoking has definite antiestrogenic effects decreasing the age of menopause and reducing the risk for developing endometrial cancer.4 Another antiestrogen drug, tamoxifen, reduces the risk for developing contralateral breast cancer in patients receiving surgical adjuvant tamoxifen therapy5 and is currently undergoing trial as a breast cancer prevention drug. These considerations suggest that the Nurses' Health Study data concerning the relationship of dietary fat to breast cancer risk be reanalyzed to include participants' smoking status. Smoking status information is available.4
Cohen MH. Breast Cancer Risk From Diet, Tobacco, and Alcohol. JAMA. 1993;269(14):1791. doi:10.1001/jama.1993.03500140042028