title: Risk of breast cancer in relation to reproductive factors in Denmark.
abstract: The effect of reproductive factors on breast cancer risk was evaluated in a population-based case-control study, including 1,486 breast cancer cases diagnosed over a one-year period in Denmark. They were identified from the files of the nationwide trial of the Danish Breast Cancer Co-operative group and the Danish Cancer Registry. The control group was an age-stratified random sample of 1,336 women from the general population. Data on risk factors were collected by self-administered (mailed) questionnaires. Significantly increased relative risks (RR) were associated with never being pregnant (RR = 1.47), an early terminated first pregnancy (RR = 1.43), and having a natural menopause after the age of 54 (RR = 1.67). Trends of decreasing risk were observed by increasing parity and age at menarche. These findings were independent of age at first full-term pregnancy which overall was not related to breast cancer risk, though a weak association appeared in women less than 50 years at diagnosis. The study confirmed that pregnancies must continue to term to offer protection against breast cancer.
authors.affiliation: Danish Cancer Society, Institute of Cancer Epidemiology, Copenhagen, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Ewertz
authors.forename: S W
authors.initials: SW
authors.lastname: Duffy
mesh_terms: D000028:Abortion, Induced; D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology*; D003276:Contraceptives, Oral; D003718:Denmark; D005260:Female; D006801:Humans; D008572:Menarche; D008593:Menopause; D008875:Middle Aged; D010298:Parity; D011247:Pregnancy; D012098:Reproduction; D012307:Risk Factors
chemical_list: D003276:Contraceptives, Oral