Does hormonal birth control (hormonal contraception) increase the risk of breast cancer?

Hormonal Birth Control and Breast Cancer Risk

Hormonal birth control is associated with a small but significant increase in breast cancer risk, with current or recent use showing a relative risk of approximately 1.2-1.3 compared to non-users. 1, 2

Evidence on Breast Cancer Risk

• Current or recent use of combined hormonal contraceptives is associated with a 20-30% increased relative risk of breast cancer compared to non-users 1, 2
• Progestagen-only contraceptives show a similar magnitude of risk increase (RR 1.21-1.29) regardless of delivery method (oral, injected, implanted, or intrauterine) 1
• The risk appears to increase with longer duration of use, from 9% with less than 1 year to 38% with more than 10 years of use 2
• After discontinuation of hormonal contraception, the risk remains elevated for women who used hormonal contraceptives for 5 years or more 2

Risk Factors and Special Populations

• Women with a family history of breast cancer do not appear to have a significantly higher risk of breast cancer with oral contraceptive use compared to women without such history 3, 4
• For carriers of BRCA1/2 genetic mutations, studies have shown conflicting results, with some showing increased risk and others showing no significant association 3
• Meta-analyses indicate that oral contraceptive use is not significantly associated with breast cancer risk in BRCA1/2 mutation carriers 3, 4
• The risk of breast cancer is greatest in women under 34 years of age, when the overall incidence of breast cancer is at its lowest 3

Absolute Risk Perspective

• The 15-year absolute excess risk associated with 5 years of hormonal contraceptive use is estimated at:
  • 8 per 100,000 users aged 16-20 years
  • 265 per 100,000 users aged 35-39 years 1
• This translates to approximately one extra breast cancer for every 7,690 women using hormonal contraception for 1 year 2

Benefits and Risk Balance

• Oral contraceptive use significantly reduces ovarian cancer risk by approximately 50% 3, 4
• Oral contraceptive use is also associated with reduced risk of endometrial cancer 3
• Colorectal cancer risk may be reduced by about 20% among women who have ever used hormonal replacement therapy, with potentially similar benefits for hormonal contraception 3

Contraceptive Recommendations Based on Age

• For women over 40, non-hormonal methods (copper IUD) or progestin-only methods are classified as Category 1 (no restrictions) 5, 6
• Combined hormonal contraceptives are classified as Category 2 (benefits generally outweigh risks) for women ≥40 years without other risk factors 5, 6
• Combined hormonal contraceptives are contraindicated (Category 4) in smokers aged ≥35 years due to increased cardiovascular risks 5, 6

Important Considerations and Pitfalls

• The risk of venous thromboembolism (VTE) is higher among oral contraceptive users than non-users, with baseline risk of 3-9 per 10,000 woman-years compared to 1-5 per 10,000 woman-years in non-users 3
• Cardiovascular risks (myocardial infarction, stroke) are increased with hormonal contraceptive use, particularly in women with additional risk factors such as smoking, diabetes, and hypertension 3, 7
• When counseling patients, it's important to present both the relative and absolute risks to provide proper context 8
• The risk-benefit assessment should consider the woman's age, family history, genetic predisposition, and other risk factors for breast cancer and cardiovascular disease 4, 8

Conclusion

While hormonal birth control does increase breast cancer risk slightly, this must be weighed against its protective effects against ovarian and endometrial cancers, as well as its effectiveness as contraception. The absolute risk increase is small, particularly in younger women, and should be considered alongside individual risk factors when making contraceptive choices.