Affiliations of authors: D. Wartenberg, Environmental and Occupational Health Sciences Institute, University of Medicine and Dentistry of New JerseyRobert Wood Johnson Medical School, Piscataway, NJ; E. E. Calle, M. J. Thun, C. W. Heath, Jr., C. Lally, American Cancer Society, Atlanta, GA; T. Woodruff, Office of Policy, U.S. Environmental Protection Agency, Washington, DC.
Correspondence to: Daniel Wartenberg, Ph.D., Environmental and Occupational Health Sciences Institute, 170 Frelinghuysen R., Piscataway, NJ 08854 (e-mail: dew{at}eohsi.rutgers.edu).
We thank Drs. Wells and Johnson for their interest in our study. They raise three important issues. First, both note that our classification of women's ETS exposure based only on the smoking habits of the spouse does not consider other sources of exposure and thus contaminates the referent group with ETS-exposed women. They contend that omission of nonspousal exposure obscures a real increase in risk among nonsmoking women whose husbands smoke. However, the assessment of risk based on nondomestic exposure to ETS does not change the results of our study. As noted in our article, we observed no association between breast cancer risk and self-reported exposure at work (rate ratio [RR] = 0.8; 95% CI = 0.6 to 1.0) or in other places (RR = 0.9; 95% CI = 0.7 to 1.2). Furthermore, even if 50% of the women who died of breast cancer who were married to never smokers (i.e., unexposed) had substantial continuous exposure to ETS outside the home, a scenario we believe unlikely, the overall association would still be less than that reported in the casecontrol studies. The absence of an exposure response relationship in our data also is not consistent with Dr. Johnson's calculations shown in his Table 1.
Second, Dr. Wells suggests that we should have broadened our reference category to include women married to light smokers as well as to nonsmokers. However, this approach would further increase misclassification in the referent group because the reference category would include some smoking spouses by design. Moreover, the association that Dr. Wells observes among women married for 31 or more years to a spouse who smokes (Table 1) is based on unadjusted death rates calculated from Table 5 in our article. The unadjusted estimate of RR = 1.26 (95% confidence limit [CI] = 0.99 to 1.59) for all never smokers in this subgroup becomes RR = 1.08 (95% CI = 0.83 to 1.41) when adjusted for age, and RR = 1.11 (95% CI = 0.85 to 1.45) with multivariate adjustment.
Third, Dr. Johnson notes that, in our comparison with results from the study by Hirayama (1) as reported by Wells (2) and the results from the study by Jee et al. (3), we used the estimates for women exposed to any passive smoke rather than specific exposure categories and may thus have underestimated the possible association of ETS with breast cancer mortality. However, we used the grouped data to improve the statistical stability of analyses based on small numbers. The instability of the RR estimates in the Hirayama study is illustrated among women aged 5069 years. The risk of breast cancer mortality among those with spouses who smoke 1519 cigarettes per day is 0.67 (95% CI = 0.25 to 1.81), whereas the risk for those with spouses who smoke 20 or more cigarettes per day is 1.82 (95% CI = 1.00 to 3.30) (2).
We believe that our original results accurately represent the passive smoking and breast cancer mortality experience of the cohort that we studied, showing no association. We further contend that the size and prospective design of the American Cancer Society study are strengths that enhance its credibility. Nonetheless, we recognize that our study design and assessment of exposure can be improved upon, for example by including adjustments for susceptibility and by developing more extensive smoking histories. Furthermore, other populations may show different patterns. We look forward to results of additional research that may help to clarify this controversial issue.
NOTES
These views represent those of the authors and do not necessarily represent those of the U.S. Environmental Protection Agency.
REFERENCES
1 Hirayama T. Cancer mortality in nonsmoking women with smoking husbands based on a large-scale cohort study in Japan. Prev Med 1984;13:68090.[Medline]
2 Wells AJ. Breast cancer, cigarette smoking, and passive smoking [letter]. Am J Epidemiol 1991;133:20810.[Medline]
3 Jee SH, Ohrr H, Kim IS. Effects of husbands' smoking on the incidence of lung cancer in Korean women. Int J Epidemiol 1999;28:8248.[Abstract]
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