Impact of menstrual and reproductive factors on breast cancer risk in Japan: Results of the JACC study

Koji Tamakoshi, Hiroshi Yatsuya, Kenji Wakai, Sadao Suzuki, Kazuko Nishio, Yingsong Lin, Yoshimitsu Niwa, Takaaki Kondo, Akio Yamamoto, Shinkan Tokudome, Hideaki Toyoshima, Akiko Tamakoshi, Mitsuru Mori, Yutaka Motohashi, Ichiro Tsuji, Yosikazu Nakamura, Hiroyasu Iso, Haruo Mikami, Yutaka Inaba, Yoshiharu HoshiyamaHiroshi Suzuki, Hiroyuki Shimizu, Yoshinori Ito, Shuji Hashimoto, Shogo Kikuchi, Akio Koizumi, Takashi Kawamura, Yoshiyuki Watanabe, Tsuneharu Miki, Chigusa Date, Kiyomi Sakata, Takayuki Nose, Norihiko Hayakawa, Takesumi Yoshimura, Akira Shibata, Naoyuki Okamoto, Hideo Shio, Yoshiyuki Ohno, Tomoyuki Kitagawa, Toshio Kuroki, Kazuo Tajima, Takashi Shimamoto, Heizo Tanaka, Shigeru Hisamichi, Masahiro Nakao, Takaichiro Suzuki, Tsutomu Hashimoto, Teruo Ishibashi, Katsuhiro Fukuda

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Abstract

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.

Original languageEnglish
Pages (from-to)57-62
Number of pages6
JournalCancer science
Volume96
Issue number1
DOIs
Publication statusPublished - 2005 Jan 1

ASJC Scopus subject areas

  • Oncology
  • Cancer Research

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    Tamakoshi, K., Yatsuya, H., Wakai, K., Suzuki, S., Nishio, K., Lin, Y., Niwa, Y., Kondo, T., Yamamoto, A., Tokudome, S., Toyoshima, H., Tamakoshi, A., Mori, M., Motohashi, Y., Tsuji, I., Nakamura, Y., Iso, H., Mikami, H., Inaba, Y., ... Fukuda, K. (2005). Impact of menstrual and reproductive factors on breast cancer risk in Japan: Results of the JACC study. Cancer science, 96(1), 57-62. https://doi.org/10.1111/j.1349-7006.2005.00010.x