CORRESPONDENCE

RESPONSE: Re: Active Smoking, Household Passive Smoking, and Breast Cancer: Evidence From the California Teachers Study

Peggy Reynolds, Susan Hurley, Debbie Goldberg
CTS Steering Committee

Affiliations of authors: Environmental Health Investigations Branch, California Department of Health Services, Oakland, CA (PR); Public Health Institute, Oakland, CA (SH, DG).

Correspondence to: Peggy Reynolds, PhD, Environmental Health Investigations Branch, California Department of Health Services, 1515 Clay St., Suite 1700, Oakland CA 94612 (e-mail: preynold{at}dhs.ca.gov)

We thank Dr. Johnson for his thoughtful comments regarding our analysis of active smoking and passive household smoking and breast cancer in the California Teachers Study (CTS). To further evaluate the influence of active smoking with respect to a first full-term pregnancy, Dr. Johnson suggested presenting our risk estimates among nulliparous women only and also stratified by the number of years of pre-partum smoking. In response, we have conducted these analyses and present the results below. As can be seen in Table 1, the patterns of risk estimates for active smoking among nulliparous women are similar to those reported for the full sample of women in our original analysis (1).Table 1 also shows our risk estimates for parous women stratified by how long a woman smoked before her first full-term pregnancy. These analyses are suggestive of a stronger smoking effect among women with longer smoking histories before their first pregnancy. However, the number of cases among women who smoked for less than 5 years pre-partum was small. When we restricted the analyses to postmenopausal breast cancers, the results were essentially the same (data not shown). The difference in risk estimates between those who smoked pre-partum for shorter compared to longer periods of time are not as dramatic as those reported by Johnson et al. in their recent research (2).


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Table 1. Adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for invasive breast cancer associated with active smoking history among members of the California Teachers Study (CTS).*

 
With respect to our passive smoking analysis, which was limited to summary indicators of household sources, we agree with Dr. Johnson that it would be valuable to take a comprehensive look at passive smoking that includes quantitative measures from all sources. Our rationale for using household passive smoking measures only was twofold. First, household passive smoking is the metric that appears most often in the literature on passive smoking exposure. Thus, our results can be compared with those from a large body of literature. Second, the detailed passive smoking data collected subsequent to the baseline questionnaire are available for only a subset of the cohort, whereas the summary indicators of household passive smoking are available for the entire cohort.

A recent descriptive analysis of the detailed passive smoking exposures in this cohort (3) suggested that, until the 1980s, the household was the major source of passive smoking exposures. Furthermore, the household was by far the most common setting for exposures experienced during childhood. If early-life exposures are most important in determining breast cancer risk, as the results of our active smoking analysis suggest, then it is likely that the summary measures of household passive smoking exposures that we used capture the majority of the passive smoking exposures of importance to breast cancer risk. Nevertheless, Dr. Johnson is correct in surmising that this cohort may have experienced significant occupational exposure to passive smoking. In fact, during the 1980s, the workplace replaced the home as the primary source of passive smoking exposures in this cohort (3).

Extremely detailed information on lifetime passive smoking exposures in the CTS is now available, and we hope to analyze these data in the near future. These data will allow us to consider quantitative measures of passive smoke exposures from household, occupational, and other settings and for various time frames during a woman’s life, which may be especially important. We also look forward to comparing these results with those from the Canadian study (2).

REFERENCES

1 Reynolds P, Hurley S, Goldberg DE et al. Active smoking, household passive smoking, and breast cancer: evidence from the California Teachers Study. J Natl Cancer Inst 2004;96:29–37.[Abstract/Free Full Text]

2 Johnson K, Pan S, Mao Y. Smoking before the first full-term pregnancy: a critical window for breast cancer risk? Presented at the 12th World Conference on Tobacco or Health, Helsinki, Finland, Aug 3–8, 2003 [abstract 300]. Geneva (Switzerland): Union Internationale Contre le Cancer (UICC); 2003.

3 Reynolds P, Goldberg DE, Hurley S, The California Teachers Study Steering Committee. Prevalence and patterns of environmental tobacco smoke exposures among California teachers. Am J Health Promot 2004;18:358–65.[ISI][Medline]



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