Association of active and passive smoking with risk of breast cancer among postmenopausal women: a prospective cohort study

Abstract

Objective To examine the association between smoking and risk of invasive breast cancer using quantitative measures of lifetime passive and active smoking exposure among postmenopausal women.

Active and passive cigarette smoking and breast cancer risk: Results from the EPIC cohort

“…In addition, only three countries out of the ten participating in EPIC asked questions about passive smoking exposure during childhood and questions about passive exposure in adulthood were limited to the time of recruitment into the study. As the comprehensiveness of the passive smoking measures has been shown to have a major impact on the magnitude of the passive smoking effect observed, 4,7,8,14,17 the measures of passive smoking exposure available in the EPIC cohort are likely to have underestimated risk associated with passive exposure and might also have diluted the active smoking risks, if some passive smokers were incorrectly classified as "unexposed." Indeed, cohort studies with better passive smoking exposure measure observed higher risk estimates in the most passively exposed women 8,23 and higher risks were also observed in premenopausal women than in postmenopausal women in studies where lifetime exposure to passive smoking was considered.…”

“…12 The relationship between smoking and breast cancer was also analyzed according to the hormone receptor status or the histological subtype of the tumor, with conflicting results. 8,[30][31][32] In this analysis, we found a slightly higher risk for ER1PR1 than for ER2PR2tumors among current active smokers. This is in line with the results published recently by Luo et al 8 and could imply that an estrogenic environment is necessary to allow carcinogenesis in cells that have been mutated by tobacco carcinogens.…”

“…When only residential exposure was available, little effect of passive smoking was shown. 19,26 When both lifetime occupational and residential exposures 23 or more quantitative measures of passive smoking exposures 8 were evaluated, an increased risk was observed. The results published on data from the Nurses' Health Study, however, did not show any increased risk with passive smoking exposure either at work or at home, but their evaluation of passive smoking exposure remained incomplete.…”

“…19 Our finding that breast cancer risk is particularly high in women who started smoking before their FFTP is in agreement with previous results from cohort studies, which demonstrated an increase in risk in women who began smoking early in life. [5][6][7][8][9][10][11]17,26,28,29 This later result, though, might be confounded by smoking duration as women who started smoking early also tend to smoke for a longer duration. In addition, residual confounding by age at first birth is also possible as women with a later first birth, and therefore a higher breast cancer risk, have more chance to have started smoking before FFTP.…”

“…2 Most epidemiological studies concluded to a weak positive association and suggested that there may be an increased risk with heavy smoking, smoking of long duration, smoking before a first full-term pregnancy (FFTP) and passive smoking. [3][4][5][6][7][8][9][10][11] A number of reports also raised the hypothesis that this increase may be stronger in women with high levels of estrogens. 12,13 Previously published reviews of the literature that included measures of passive smoking concluded that passive smokers (and particularly premenopausal women) may be at increased risk of developing breast cancer when compared to women never regularly exposed to tobacco smoke in any form.…”