title: No increase in breast cancer risk in Japanese women taking oral contraceptives: a case-control study investigating reproductive, menstrual and familial risk factors for breast cancer.
abstract: BACKGROUND
  Low-dose oral contraceptives (OC) were approved by the Japanese Ministry of Health, Labor and Welfare in 1999, yet despite their contraceptive and non-contraceptive health benefits, only 5% of the target population use them. Fear of increased cancer risk, particularly breast cancer, is one reason for this. Due to low OC uptake and low screening participation, a paucity of data is available on the risk of OC use and breast cancer in Japanese women. The present study investigated OC use and breast cancer risk, as well as menstrual, reproductive and family factors.
  
  
  METHODS
  This was a clinic-based case-control study of women aged 20-69yrs who had undergone breast screening between January 2007 and December 2013 in central Tokyo. In all, 28.8% of the participants had experience with OC use. Cases were 155 women with a pathologically confirmed diagnosis of breast cancer. Controls were the remaining 12,333 women.
  
  
  RESULTS
  Increased age was a significant risk factor for breast cancer (p<0.001). A lower risk was found in premenopausal women presently taking OC compared to never users (OR 0.45; 95% CI 0.22-0.90) after adjusting for age, parity and breast feeding, and a family history of breast cancer.
  
  
  CONCLUSIONS
  Increased age rather than OC use had a greater effect on breast cancer risk. This risk may be decreased in premenopausal women with OC use, but further long-term prospective studies are necessary.
authors.affiliation: Tsushima Ruriko Women's Life Clinic Ginza, Kyoto, Japan E-mail : w-breast@w-wellness.com.
authors.forename: Miho
authors.initials: M
authors.lastname: Ichida
authors.forename: Akemi
authors.initials: A
authors.lastname: Kataoka
authors.forename: Ruriko
authors.initials: R
authors.lastname: Tsushima
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Taguchi
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000139:chemically induced* / Q000453:epidemiology*; D016022:Case-Control Studies; D003276:Contraceptives, Oral / Q000009:adverse effects*; D005260:Female; D005500:Follow-Up Studies; D020022:Genetic Predisposition to Disease; D006801:Humans; D008598:Menstruation; D008875:Middle Aged; D011379:Prognosis; D012098:Reproduction; D012307:Risk Factors; D013997:Time Factors; D055815:Young Adult
chemical_list: D003276:Contraceptives, Oral