SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. It is estimated that in the US, approximately 316,950 new cases of female breast cancer will be diagnosed in 2025, and about 42,170 women will die of the disease, largely due to metastatic recurrence.
The tumor suppressor genes such as BRCA1 and BRCA2 help repair damaged DNA and thus play an important role in maintaining cellular genetic integrity, failing which these genetic aberrations can result in malignancies. Mutations in BRCA1 and BRCA2 account for about 20 to 25 percent of hereditary breast cancers and about 5 to 10 percent of all breast cancers. These mutations can be inherited from either of the parents and a child has a 50 percent chance of inheriting this mutation, and the deleterious effects of the mutations are seen even when a second copy of the gene in an individual is normal. Women with germline BRCA1 or BRCA2 mutations face markedly elevated lifetime risks of breast cancer, estimated at up to 70%. More than half of these cancers occur before the age of 50, underscoring the importance of informed counseling regarding risk-modifying exposures. One such factor is hormonal contraception, widely used for birth control and non-contraceptive health benefits, but also a potential contributor to breast cancer risk. The present study was conducted to assess the association between use of any hormonal contraception and breast cancer risk for BRCA1 and BRCA2 mutation carriers using individual participant data from four prospective cohorts.
Study Design
A large observational analysis pooled data from four prospective cohorts across Australia, New Zealand, Europe, Canada, and the United States (kConFab FUP, BCFR, RFS, and the UPenn Registry). The study included 3,882 women with BRCA1 mutations and 1,509 with BRCA2 mutations who were followed for a median of approximately six years. Associations between hormonal contraception use and breast cancer incidence were assessed using Cox regression modeling.
Key Findings
- Hormonal Contraception use prevalence: 53% of BRCA1 carriers and 71% of BRCA2 carriers reported 1 year or more of use (median duration, 4.8 and 5.7 years, respectively). Hormonal contraceptives included birth control pills, patches, implants, injections, vaginal rings, and IUDs containing any hormones.
- Cancer incidence: During follow-up, 488 BRCA1 and 191 BRCA2 carriers developed breast cancer during median follow-up of 5.9 and 5.6 years, respectively.
- BRCA1 mutation carriers:
- Ever use of hormonal contraception was associated with a 29% increased relative risk of breast cancer (HR, 1.29; 95% CI, 1.04–1.60).
- Longer cumulative use conferred higher risk, with an estimated 3% increase in risk per additional year of use.
- Current use and recent use were not independently significant, but a dose–response relationship emerged with duration.
- BRCA2 mutation carriers: No significant association was observed between hormonal contraception use and breast cancer risk (HR for ever use, 1.07; 95% CI, 0.73–1.57). However, the relatively small number of events limits certainty.
Absolute Risk Implications
For BRCA1 carriers, small relative increases translate into substantial absolute risk shifts due to their high baseline susceptibility. For example, modeling suggested that an 18-year-old BRCA1 carrier with a family history of breast cancer would at age 58 face:
- 51.3% lifetime risk without hormonal contraception use,
- 56.6% with 5 years of use,
- 62.0% with 10 years of use,
- 67.3% with 15 years of use.
Shorter-term use was associated with minimal increases in absolute risk, whereas prolonged exposure yielded more clinically meaningful elevations.
Context and Clinical Considerations
- Findings align with evidence in the general population showing modest increases in breast cancer risk with hormonal contraception use, though the higher baseline risk in BRCA1 carriers amplifies the absolute impact.
- The lack of association for BRCA2 carriers should be interpreted cautiously due to limited statistical power.
- Importantly, while oral contraceptives reduce tubo-ovarian cancer risk, this benefit may be less relevant for BRCA1/2 carriers who undergo guideline-recommended risk-reducing salpingo-oophorectomy by ages 35–45.
- Study strengths include large BRCA1 cohort size, prospective data collection, and consistent findings across international cohorts. Limitations include observational design, potential misclassification of hormonal contraception type, and limited data beyond 15 years of use.
Take-Home Message for Oncologists
Hormonal contraceptives appear to increase breast cancer risk for BRCA1 mutation carriers, particularly with longer cumulative use, while evidence for BRCA2 remains inconclusive. When counseling patients, absolute risk estimates and individual values should guide decisions. Shorter-term use may be acceptable for some women, but prolonged use could confer risk increases that outweigh potential benefits.
Hormonal Contraception and Breast Cancer Risk for Carriers of Germline Mutations in BRCA1 and BRCA2. Phillips K-A, Kotsopoulos J, Domchek SM, et al. J Clin Oncol. 2025;43:422-431
