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Oral contraceptives and breast cancer risk in the International BRCA1/2 Carrier Cohort Study (IBCCS)


The marked reduction of the risk of breast cancer following a prophylactic oophorectomy illustrates that endogenous hormones play an important role in the etiology of breast cancer among BRCA1/2 mutation carriers, as they do in the general population. In the general population the use of oral contraceptives has been associated with a slightly increased risk. Little is so far known about the safety of oral contraceptives among BRCA1/2 carriers, who have much higher premenopausal background rates of breast cancer.


A retrospective cohort study was performed using an international cohort of 1601 BRCA1/2 mutation carriers. A time-dependent proportional hazard Cox regression was used, stratified for birth cohort, gene, country of residence and relatedness. All analyses were adjusted for prophylactic oophorectomy and number of full-term pregnancies. To reduce possible testing bias, the analyses were weighted to achieve the rate of breast cancer within the cohort as a priori estimated for BRCA1/2 mutation carriers.


We found a slightly increased risk of breast cancer for BRCA/12 mutation carriers who ever used oral contraceptives, with an adjusted hazard ratio of 1.47 (95% confidence interval = 1.16-1.87). The risk increase did not vary according to various aspects of oral contraceptive use, such as time since stopping, duration of use, age at start, and calendar year at start. In addition, the risk increase was similar for BRCA1 and BRCA2 mutation carriers.


Use of oral contraceptives seems to be associated with a slightly increased relative risk of breast cancer among BRCA1/2 mutation carriers, comparable with the general population. However, due to the high background rates of breast cancer among BRCA1/2 carriers, oral contraceptive use may result in a considerable absolute excess risk of breast cancer, if the association is causal.


This work was supported by NIH Award CA81203, Cancer Research UK, the INHERIT BRCAs research program, the Fondation de France and the Ligue Nationale Contre le Cancer, and the Dutch Cancer Society.

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Rookus, M., Brohet, R., Andrieu, N. et al. Oral contraceptives and breast cancer risk in the International BRCA1/2 Carrier Cohort Study (IBCCS). Breast Cancer Res 7 (Suppl 2), P1.10 (2005).

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  • Breast Cancer
  • Breast Cancer Risk
  • Oral Contraceptive
  • Mutation Carrier
  • Birth Cohort