What is the relationship between breast cancer and the use of hormonal contraceptives (birth control)?

From the Guidelines

The use of hormonal contraceptives is generally contraindicated in breast cancer survivors, and alternative non-hormonal contraception methods should be considered. The evidence from the 2020 eso-esmo 4th international consensus guidelines for breast cancer in young women 1 suggests that exogenous hormonal contraception may increase the risk of breast cancer, and its use is controversial. A large epidemiological study has suggested that the use of levonorgestrel-releasing intrauterine device (IUD) may increase the risk of developing breast cancer, although a meta-analysis of three randomized clinical trials did not show an increased incidence in breast cancer recurrence and cancer-induced death.

In the context of breast cancer, the risk of hormonal contraceptives outweighs the benefits, and alternative methods such as barrier methods (e.g., condoms, cervical diaphragm) or copper IUDs should be recommended. The 2010 U.S. Medical Eligibility Criteria for Contraceptive Use 1 also classifies the use of progestin-only contraceptives, including progestin-only pills, DMPA, and implants, as category 4 for current breast cancer, indicating that the risk of using these methods outweighs the benefits.

Key points to consider when counseling breast cancer survivors about contraception include:

• The risk of hormonal contraceptives in breast cancer survivors
• The importance of alternative non-hormonal contraception methods
• The need for regular breast cancer screening according to age-appropriate guidelines
• The consideration of fertility preservation strategies for young women with breast cancer.

From the Research

Breast Cancer Risk in Contraceptive Users

• The evidence suggests that the use of hormonal contraceptives may be associated with an increased risk of breast cancer, with a pooled analysis of studies finding that only current or recent users were at higher risk of breast cancer 2.
• A nationwide prospective cohort study in Denmark found that the relative risk of breast cancer among all current and recent users of hormonal contraception was 1.20 (95% confidence interval [CI], 1.14 to 1.26), with the risk increasing from 1.09 (95% CI, 0.96 to 1.23) with less than 1 year of use to 1.38 (95% CI, 1.26 to 1.51) with more than 10 years of use 3.
• Another study found that the risk of breast cancer was higher among women who currently or recently used contemporary hormonal contraceptives than among women who had never used hormonal contraceptives, and this risk increased with longer durations of use 3.
• However, the absolute increases in risk were small, with an overall absolute increase in breast cancers diagnosed among current and recent users of any hormonal contraceptive of 13 (95% CI, 10 to 16) per 100,000 person-years, or approximately 1 extra breast cancer for every 7690 women using hormonal contraception for 1 year 3.
• The risk of breast cancer associated with hormonal contraception use has been found to wane with time, and in the long term, hormonal contraception use has been found not to be associated with any increased total cancer risk 4.

Factors Influencing Breast Cancer Risk

• The risk of breast cancer appears to be increased only minimally among current oral contraceptive users, with well-designed studies showing that the incidence of thromboembolic disease is related to the estrogen dose and that the risk of thromboembolism is highest in women who smoke 5.
• The use of combined estrogen and progestin therapy has been found to increase breast cancer risk by as much as 10% per year of use, while the use of progestin-only contraceptives may also increase the risk of breast cancer 2, 3.
• The risk of breast cancer associated with hormonal contraception use may be influenced by the type and duration of use, as well as individual factors such as age and smoking status 2, 3, 5.

Comparison of Studies

• The findings of the studies are generally consistent, with most studies finding an increased risk of breast cancer associated with hormonal contraception use 2, 3, 4.
• However, the magnitude of the risk and the factors influencing it may vary between studies, highlighting the need for further research to fully understand the relationship between hormonal contraception use and breast cancer risk 2, 3, 4.