title: Reproductive factors, exogenous female hormone use and breast cancer risk in Japanese: the Miyagi Cohort Study.
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.
authors.affiliation: Division of Surgical Oncology, Graduate School of Medicine, Tohoku University, Sendai, Miyagi, 980-8574, Japan.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Kawai
authors.forename: Yuko
authors.initials: Y
authors.lastname: Minami
authors.forename: Shinichi
authors.initials: S
authors.lastname: Kuriyama
authors.forename: Masako
authors.initials: M
authors.lastname: Kakizaki
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Kakugawa
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Nishino
authors.forename: Takanori
authors.initials: T
authors.lastname: Ishida
authors.forename: Akira
authors.initials: A
authors.lastname: Fukao
authors.forename: Ichiro
authors.initials: I
authors.lastname: Tsuji
authors.forename: Noriaki
authors.initials: N
authors.lastname: Ohuchi
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000453:epidemiology*; D015331:Cohort Studies; D005260:Female; D020249:Hormone Replacement Therapy; D006801:Humans; D007564:Japan; D008875:Middle Aged; D017698:Postmenopause / Q000378:metabolism; D017584:Reproductive History; D012307:Risk Factors