| Summary: | Introduction
The role of cigarette smoking on breast cancer risk remains
controversial, due to its dual carcinogenic-antiestrogenic action.
Methods
In the population-based multi-case-control study (MCC-Spain), we
collected epidemiological and clinical information for 1733 breast cancer cases
and 1903 controls, including smoking exposure. The association with breast
cancer, overall, by pathological subtype and menopausal status, was assessed
using logistic and multinomial regression models.
Results
Smokers had higher risk of premenopausal breast cancer, particularly if they
had smoked ≥30 years (AOR=1.75; 95% CI: 1.04–2.94), although most estimates
did not achieve statistical significance. In contrast, among postmenopausal women,
smoking was associated with lower risk of breast cancer, mainly in overweight and
obese women. The strongest risk reductions were observed among postmenopausal
women who had stopped smoking ≥10 years before cancer diagnosis, particularly
for HER2+ tumors (AOR=0.28; 95% CI: 0.11–0.68); p for heterogeneity = 0.040).
Also, those who had smoked <10 pack-years (AOR=0.68; 95% CI: 0.47–0.98) or
10–25 pack-years (AOR=0.62; 95% CI: 0.42–0.92) during their lifetime were
at a reduced risk of all breast cancer subtypes (p for heterogeneity: 0.405 and
0.475, respectively); however, women who had smoked more than 25 pack-years
showed no reduced risk.
Conclusions
Menopausal status plays a key role in the relationship between tobacco
and breast cancer for all cancer subtypes. While smoking seems to increase the
risk in premenopausal woman, it might be associated to lower risk of breast cancer
among postmenopausal women with excess weight.
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