Use of hormonal contraceptive pills may be associated with increased risk of breast cancer
While the 20% increased risk among women using contemporary formulations of oral contraceptives is similar to that initially reported among users of older formulations, an editorial noted, the finding that breast cancer risk continues to be elevated for five years or more should be regarded as preliminary because the increase in risk would not have remained significant after adjustment.
Compared to women who have never used hormonal contraceptives, current and recent users may be at increased risk of breast cancer, a recent study found.
Researchers prospectively followed a cohort of all women in Denmark who were between ages 15 and 49 years (n=1.8 million) for a total of 19.6 million person-years. Eligible women had not had cancer or venous thromboembolism and had not received treatment for infertility. Results were published online on Dec. 7 by The New England Journal of Medicine.
A total of 11,517 cases of breast cancer were diagnosed during an average follow-up of 10.9 years. Compared to those who had never used hormonal contraception, current and recent users had a relative risk of breast cancer of 1.20 (95% CI, 1.14 to 1.26). The relative risk increased with duration of use, 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 (P=0.002). The risk remained elevated in previous users for at least five years compared to nonusers.
The estimated relative risk associated with oral combination (estrogen-progestin) contraceptives varied between 1.0 and 1.6. Current or recent users of the progestin-only intrauterine system also had a higher risk of breast cancer than women who had never used hormonal contraceptives (relative risk, 1.21; 95% CI, 1.11 to 1.33). The absolute increase in breast cancer cases among current and recent users of any hormonal contraceptive was 13 (95% CI, 10 to 16) per 100,000 person-years, or about one extra breast cancer diagnosis per year for every 7,690 women using hormonal contraception.
The authors noted limitations of the study, such as the inability to adjust for certain factors (e.g., breastfeeding, alcohol consumption, physical activity) and a lack of information on exposure to hormonal contraceptives before study entry.
The 20% increased risk among women using contemporary formulations of oral contraceptives is similar to that initially reported among users of older formulations, an accompanying editorial noted. However, the finding that breast cancer risk continues to be elevated for five years or more should be regarded as preliminary because the increase in risk would not have remained significant after adjustment, the editorial stated.
The higher risk seen in users of hormonal contraceptives “must be placed in the context of the low incidence rates of breast cancer among younger women … [and] needs to be balanced against the benefits of the use of oral contraceptives,” the editorialist wrote.