Understanding combined oral contraceptives and breast cancer risk

In a recent interview, Mitchell Creinin, MD, director of the Complex Family Planning Fellowship at the University of California Davis Health, discussed the association between combined oral contraceptive (COC) use and breast cancer risk.

For decades, COCs only contained the estrogen ethinylestradiol (EE). However, the amount of EE included in COCs has decreased over time, with the aim of decreasing venous thromboembolism (VTE) risk.

Data has indicated the risk of VTE is not impacted when shifting extremely low doses, but irregular bleeding risk increases when decreasing dosages at this level. This has led irregular bleeding to be the most common reason for discontinuation among COC users.

While an association has been established between COC use and increased breast cancer risk, the details of this association are unclear. The literature available primarily focuses on COCs containing EE, which is the main source of breast cancer risk. As COCs incorporate new estrogens such as estradiol and estetrol, those risks may not be present.

Literature has found the risk of breast cancer increases 20% to 30% from COC use. However, these studies primarily evaluate breast cancer risk over a 10-year period. Lifetime breast cancer and breast cancer mortality risk does not increase from COC use, with breast cancer risk decreasing to normal levels after discontinuation of an EE-containing COC.

As an example, Creinin discussed how the risk of breast cancer would be impacted in the average patient aged 30 years old. The baseline risk in this patient would be approximately 0.49%, increasing to approximately 0.64% from COC.

This indicates a minimally increased risk. Though the risk may increase in older patients, regular screening for breast cancer is recommended in these populations, providing additional support.

Creinin noted the significant benefits of COC use for pregnancy prevention, bleeding abnormality treatment, menstrual-related symptoms, and other conditions. Blood clot risk and concerns over breast cancer have been identified as common risk factors, but clinicians can explain the minimally increased breast cancer risk to their patients.

Additional information about this topic is included by an article written by Creinin alongside Seema A. Khan, MD, titled, “Contemporary understanding of breast cancer risk with combined oral contraceptives.”