Open AccessImpact of menstrual and reproductive factors on breast cancer risk in Japan: Results of the JACC study
Author(s) -
Tamakoshi Koji,
Yatsuya Hiroshi,
Wakai Kenji,
Suzuki Sadao,
Nishio Kazuko,
Lin Yingsong,
Niwa Yoshimitsu,
Kondo Takaaki,
Yamamoto Akio,
Tokudome Shinkan,
Toyoshima Hideaki,
Tamakoshi Akiko
Publication year - 2005
Publication title -
cancer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.035
H-Index - 141
eISSN - 1349-7006
pISSN - 1347-9032
DOI - 10.1111/j.1349-7006.2005.00010.x
Subject(s) - medicine , breast cancer , menarche , gynecology , demography , obstetrics , relative risk , proportional hazards model , parity (physics) , menopause , cohort study , population , cohort , cancer , confidence interval , environmental health , physics , particle physics , sociology
The incidence of breast cancer among Japanese women, a traditionally low‐risk population, has increased substantially. To evaluate the association of reproductive factors with breast cancer risk, we examined 38 159 Japanese women, aged 40–79 years, who responded to a questionnaire on reproductive and other lifestyle factors from 1988 to 1990 in the Japan Collaborative Cohort Study. During an average 7.6 years of follow‐up, we documented 151 incidents of breast cancers. Cox proportional hazards modeling was employed to estimate relative risks (RR) and 95% confidence intervals (CI). There was a significant decline in the risk of breast cancer with increasing parity among parous women (trend P = 0.01). Women with four or more parities had a 69% lower risk than uniparous women, a reduced risk was also evident among menopausal women. Breast cancer risk tended to rise with increasing age at first delivery (trend P = 0.05), the association being very apparent among menopausal women (trend P = 0.02). Compared to the women who had their first delivery before age 25, those who delayed this event until after age 34 had an RR of 2.12 (95% CI: 0.72–6.21) and 3.33 (1.07–10.3) among the overall subjects and the menopausal, respectively. There was no apparent association of breast cancer risk with age at menarche or menopause. Our study concerning reproductive risk factors suggests that breast cancer in Japan is similar to that in Western countries, and that reproductive factors, particularly the number of parity and age at first delivery, might be important in the etiology of breast cancer among Japanese women. ( Cancer Sci 2005; 96: 57–63)