title: Leisure-time physical activity and breast cancer risk defined by estrogen and progesterone receptor status--the Japan Public Health Center-based Prospective Study.
abstract: OBJECTIVE
  The study aims to investigate the association between leisure-time physical activity and breast cancer risk in consideration of tumor estrogen-receptor/progesterone-receptor status.
  
  
  METHODS
  We conducted a population-based prospective cohort study among 53,578 women in the Japan Public Health Center-based Prospective Study. Leisure-time physical activity was assessed by self-reported questionnaires. A Cox proportional hazards regression model was used to derive relative risks and 95% confidence intervals.
  
  
  RESULTS
  From 1990-1993 to the end of 2007, 652 cases were identified. The breast cancer rates (per 100,000 person-years) in the sedentary groups (≤3 days/month) was 84 in overall, 97 in premenopausal and 75 in postmenopausal women. We observed a statistically significant inverse association between leisure-time physical activity and breast cancer risk (relative risk(≥3 days/week vs. ≤3 days/month)=0.73; 95% confidence interval 0.54-1.00; p(trend) 0.037), particularly in estrogen receptor+progesterone receptor+ (relative risk 0.43; 0.19-1.00; p(trend) 0.022), and this inverse trend was apparent among postmenopausal women (relative risk 0.25; 0.06-1.06; p(trend) 0.041). An inverse trend was also observed between daily total physical activity and postmenopausal estrogen receptor+progesterone receptor+ risk (p=0.046). Among body mass index ≥25 kg/m(2) group, leisure-time physical activity was associated with decreased risk (relative risk(≥1 day/week vs. ≤3 days/month)=0.65; 0.43-0.97; p(trend) 0.033).
  
  
  CONCLUSIONS
  Active participation in leisure-time physical activity may contribute to a decrease in breast cancer risk, particularly for postmenopausal estrogen receptor+progesterone receptor+ tumors.
authors.affiliation: Epidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, 5-1-1 Tsukiji, Tokyo, 104-0045, Japan.
authors.forename: Reiko
authors.initials: R
authors.lastname: Suzuki
authors.forename: Motoki
authors.initials: M
authors.lastname: Iwasaki
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Yamamoto
authors.forename: Manami
authors.initials: M
authors.lastname: Inoue
authors.forename: Shizuka
authors.initials: S
authors.lastname: Sasazuki
authors.forename: Norie
authors.initials: N
authors.lastname: Sawada
authors.forename: Taiki
authors.initials: T
authors.lastname: Yamaji
authors.forename: Taichi
authors.initials: T
authors.lastname: Shimazu
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Tsugane
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis; D015992:Body Mass Index; D001943:Breast Neoplasms / Q000737:chemistry / Q000453:epidemiology / Q000209:etiology*; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D007899:Leisure Activities; D008593:Menopause; D009043:Motor Activity; D016016:Proportional Hazards Models; D011446:Prospective Studies; D011960:Receptors, Estrogen / Q000032:analysis*; D011980:Receptors, Progesterone / Q000032:analysis*; D012307:Risk Factors
chemical_list: D014408:Biomarkers, Tumor; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone