Reproductive factors,exogenous female hormone use and breast cancer risk in Japanese: the Miyagi Cohort Study |
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Authors: | Masaaki Kawai Yuko Minami Shinichi Kuriyama Masako Kakizaki Yoichiro Kakugawa Yoshikazu Nishino Takanori Ishida Akira Fukao Ichiro Tsuji Noriaki Ohuchi |
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Institution: | (1) Division of Surgical Oncology, Graduate School of Medicine, Tohoku University, 1-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8574, Japan;(2) Division of Community Health, Tohoku University School of Health Sciences, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575, Japan;(3) Division of Epidemiology, Department of Public Health and Forensic Medicine, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575, Japan;(4) Division of Surgery, Miyagi Cancer Center, 47-1, Nodayama, Medeshima-Shiode, Natori, Miyagi 981-1293, Japan;(5) Division of Epidemiology, Miyagi Cancer Center Research Institute, 47-1, Nodayama, Medeshima-Shiode, Natori, Miyagi 981-1293, Japan;(6) Department of Public Health, Yamagata University School of Medicine, 2-2-2, Iida-nishi, Yamagata 990-9585, Japan; |
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Abstract: | The incidence of breast cancer among Japanese women is substantially increasing. This population-based prospective cohort
study in Japan evaluated the associations of reproductive factors and exogenous female hormone use with breast cancer risk,
both overall and separately among premenopausal and postmenopausal women. A total of 24,064 women aged 40–64 were followed
from 1990 to 2003. During 309,424 person-years of follow-up, 285 breast cancer cases were documented. In overall evaluation,
nulliparity was significantly associated with an increased risk of breast cancer. There was a significant decrease in risk
with increasing parity number among parous women (trend P = 0.008). No association was observed between age at menarche or age at first birth and breast cancer risk. Neither oral
contraceptive (OC) use nor the use of exogenous female hormones other than OC was associated with breast cancer risk. The
evaluation according to menopausal status revealed that nulliparity and parity number were significantly related to breast
cancer risk only among postmenopausal women. Later age at natural menopause was associated with an increased risk of breast
cancer among postmenopausal women (trend P = 0.02). Our findings suggest that parity number and age at menopause have great effects on breast cancer risk among Japanese
women. |
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