能動喫煙、とくに第1子出産前の喫煙は、乳がんのリスクを中等度上昇させる。

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2011年01月26日(Wed) 15:12

Early Cigarette Smoking Associated with Breast Cancer

Young female patients who smoke may benefit from knowing that early smoking is associated
with a modest increase in breast cancer risk, according to an Archives of Internal Medicine study.

Researchers analyzing updated data from the Nurses' Health Study report that they have
confirmed their 2002 finding of a slight elevation in breast cancer risk associated with smoking.
During some 3 million person-years of follow-up between 1976 and 2006, women who smoked
more than 25 cigarettes per day for more than 35 years and began smoking before age 18 had
a hazard ratio for invasive breast cancer of 1.25, compared with never-smokers.

The effect was stronger when smoking began before the woman's first birth and before menopause.
Postmenopausal smoking was associated with a slightly decreased risk. There was no apparent
increased risk from exposure to secondhand smoke.

Cigarette Smoking and the Incidence of Breast Cancer

Fei Xue, MD, ScD; Walter C. Willett, MD, DrPH; Bernard A. Rosner, PhD; Susan E.
Hankinson, ScD; Karin B. Michels, ScD, PhD

Arch Intern Med. 2011;171(2):125-133. doi:10.1001/archinternmed.2010.503

Background 

Tobacco smoke contains carcinogens, which may increase the risk of
breast cancer (BC). Conversely, cigarette smoking also has antiestrogenic effects,
which may reduce the risk of BC. The association between smoking and BC remains
controversial.

Methods 

Prospective cohort study of 111 140 participants of the Nurses' Health
Study from 1976 to 2006 for active smoking and 36 017 women from 1982 to 2006
for passive smoking.

Results 

During 3 005 863 person-years of follow-up, 8772 incident cases of
invasive BC were reported. After adjustment for potential confounders, the hazard
ratio (HR) of BC was 1.06% (95% confidence interval [CI], 1.01%-1.10%) for ever
smokers relative to never smokers. Breast cancer incidence was associated with
a higher quantity of current (P for trend = .02) and past (P for trend = .003)
smoking, younger age at smoking initiation (P for trend = .01), longer duration
of smoking (P for trend = .01), and more pack-years of smoking (P for trend = .005).
Premenopausal smoking was associated with a slightly higher incidence of
BC (HR, 1.11; 95% CI, 1.07-1.15 for every increase of 20 pack-years),
especially smoking before first birth (1.18; 1.10-1.27 for every increase of
20 pack-years). Conversely, the direction of the association between postmenopausal
smoking and BC was inverse (0.93; 0.85-1.02 for every increase of 20 pack-years).
Passive smoking in childhood or adulthood was not associated with BC risk.

Conclusion 

Active smoking, especially smoking before the first birth, may be
associated with a modest increase in the risk of BC.

能動喫煙、とくに第1子出産前の喫煙は、乳がんのリスクを中等度上昇させる。

Author Affiliations: Obstetrics and Gynecology Epidemiology Center, Department
of Obstetrics and Gynecology (Drs Xue and Michels), and the Channing Laboratory,
Department of Medicine (Drs Willett, Rosner, Hankinson, and Michels),
Brigham and Woman's Hospital, and Harvard Medical School, Boston, Massachusetts;
and Departments of Epidemiology (Drs Xue, Willett, Rosner, Hankinson, and Michels),
Nutrition (Dr Willett), and Biostatistics (Dr Rosner), Harvard School of Public
Health, Boston.


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