Active smoking, passive smoking, and breast cancer risk: findings from the Japan Collaborative Cohort Study for Evaluation of Cancer Risk.
BACKGROUND
Evidence is lacking regarding the relationship between cigarette smoking and breast cancer in Japanese women. We examined the association between breast cancer incidence and active and passive smoking in the Japan Collaborative Cohort Study for Evaluation of Cancer Risk.


METHODS
Our study comprised 34,401 women aged 40-79 years who had not been diagnosed previously with breast cancer and who provided information on smoking status at baseline (1988-1990). The subjects were followed from enrollment until December 31, 2001. Cox proportional-hazards models were used to estimate the hazard ratio (HR) and 95% confidence interval (CI) for the association between breast cancer incidence and tobacco smoke.


RESULTS
During 271,412 person-years of follow-up, we identified 208 incident cases of breast cancer. Active smoking did not increase the risk of breast cancer, with a HR for current smokers of 0.67 (95% CI: 0.32-1.38). Furthermore, an increased risk of breast cancer was not observed in current smokers who smoked a greater number of cigarettes each day. Overall, passive smoking at home or in public spaces was also not associated with an increased risk of breast cancer among nonsmokers. Women who reported passive smoking during childhood had a statistically insignificant increase in risk (HR: 1.24; 95% CI: 0.84-1.85), compared with those who had not been exposed during this time.


CONCLUSIONS
Smoking may not be associated with an increased risk of breast cancer in this cohort of Japanese women.
Lin
Yingsong
Y
Department of Public Health, Aichi Medical University School of Medicine, Aichi, Japan.
Kikuchi
Shogo
S
Tamakoshi
Koji
K
Wakai
Kenji
K
Kondo
Takaaki
T
Niwa
Yoshimitsu
Y
Yatsuya
Hiroshi
H
Nishio
Kazuko
K
Suzuki
Sadao
S
Tokudome
Shinkan
S
Yamamoto
Akio
A
Toyoshima
Hideaki
H
Mori
Mitsuru
M
Tamakoshi
Akiko
A
D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology*; D015331:Cohort Studies; D015897:Comorbidity; D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D008875:Middle Aged; D016017:Odds Ratio; D011159:Population Surveillance; D016016:Proportional Hazards Models; D012107:Research Design; D018570:Risk Assessment; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology*; D014028:Tobacco Smoke Pollution / Q000706:statistics & numerical data*; D016387:Women's Health
D014028:Tobacco Smoke Pollution