University of Copenhagen, Denmark
Øjvind Lidegaard is a Clinical Professor with expertise in Obstetrics & Gynaecology in University of Copenhagen, Denmark.
Background: We know little about the risk of breast cancer in users of newer types of hormonal contraception and in users of hormone intrauterine devices.
Methods: We assessed associations between hormonal contraception use and invasive breast cancer risk in a nationwide prospective cohort study following all women in Denmark aged 15–49 years without previous cancer, venous thromboembolism, or infertility treatment. Nationwide Registers provided individually updated information about use of hormonal contraception, breast cancer diagnoses, and information on potential confounders.
Results: Among 1.8 million women followed on average for 10.9 years with a total of 19.6 million person-years, 11,517 breast cancers occurred. Compared to never users, the relative risk of breast cancer among all current and recent users was 1.2 (95% CI 1.1-1.3), increasing from 1.1 (1.0-1.2) with less than one year of use to 1.4 (1.3-1.5) with more than ten years of use. There was little evidence that the risk varied by type of progestogen in the combined formulations. Current or recent users of the progestin-only intrauterine system also experienced an increased relative risk of breast cancer of 1.2 (1.1-1.3).
The overall absolute mean increase in breast cancers among current and recent users of any hormonal contraceptive for all ages was 13 (10-16) per 100,000 person-years; approximately one extra breast cancer for every 7690 women using hormonal contraception for one year; the absolute risk difference increased by age.
Conclusion: Breast cancer risk was increased among current and recent users of contemporary hormonal contraception and increased with longer durations of use; however, absolute increases in risk were small, and the same products protects against ovarian cancer.