Oral contraceptive use and risk of breast cancer among women with a family history of breast cancer: A prospective cohort study

Stephanie A.N. Silvera, Anthony B. Miller, Thomas E. Rohan

Research output: Contribution to journalArticle

37 Scopus citations

Abstract

Family history of breast cancer is an established risk factor for breast cancer. In addition, there is evidence that oral contraceptive use may be associated with a moderate increase in breast cancer risk. The three cohort studies that have investigated the relationship between oral contraceptive use and breast cancer risk among women with a family history of breast cancer have yielded mixed results, possibly due to the relatively small sample sizes employed and/or differences in the selection of covariates for inclusion in multivariate models. Therefore, we examined the association between oral contraceptive use and breast cancer risk in a large cohort study in Canada. The cohort consisted of the 27,318 women in the Canadian National Breast Screening Study who reported a family history of breast cancer on enrolment into the study. Linkages to national mortality and cancer databases yielded data on deaths and cancer incidence, with follow-up ending between 1998 and 2000, depending upon the province. During a mean of 16.0 years of follow-up, we observed 1707 incident cases of breast cancer among women with any history of breast cancer of which 795 cases occurred among women with a mother, sister, and/or daughter with breast cancer. Among women with any family history of breast cancer, ever use of oral contraceptives was associated with a 12% reduction in risk of breast cancer (95% confidence interval [CI]=0.73-1.07), and there was an inverse trend with increasing duration of use of borderline statistical significance (p trend=0.03). Although we also observed a 25% lower risk of breast cancer associated with oral contraceptive use of greater than 84 months versus never use among women with a first degree relative with breast cancer, this finding was not statistically significant (95% CI=0.47-1.19, p trend=0.48). Our data raise the possibility that relatively long duration of oral contraceptive use may be inversely associated with risk among women with a family history of breast cancer.

Original languageEnglish
Pages (from-to)1059-1063
Number of pages5
JournalCancer Causes and Control
Volume16
Issue number9
DOIs
StatePublished - 1 Nov 2005

Keywords

  • Breast neoplasm
  • Family history
  • National Breast Screening Study
  • Oral contraceptives
  • Prospective cohort

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