Study: Progestin birth control may slightly increase breast cancer risk

Relevance: Medium-High

Strength of Science: High

Research Timeline: Post Approval

Relevance Rating Details

What is this study about?

This study found that birth control that contains only the hormone progestin slightly increases a person’s risk of developing breast cancer. The researchers found that the increased risk is similar for different forms of progestin birth control (pill, shot, patch or intrauterine device) and decreases over time after you stop using the birth control. This small increase in risk is similar to the slightly increased risk associated with birth control methods that include both estrogen and progestin.

Why is this study important?

Hormonal birth control is very effective. Contraceptive pills, shots, implants and intrauterine devices (IUDs) use progestin only or a combination of the hormones estrogen and progestin.

Previous studies have found that recent use of birth control using a combination of estrogen and progestin slightly increases the risk of breast cancer. However, this increased risk declines after people stop using this type of birth control. Ten years after stopping this type of birth control, breast cancer risk is no longer increased.

When choosing birth control, people often weigh the pros and cons of each method. A person’s cancer risk may influence their decision. Until now, doctors did not know how birth control containing progestin only affects breast cancer risk. The new information from this study will be useful to people choosing what kind of birth control to use.

Study findings

This study looked at the prescription history for hormonal birth control among people with breast cancer. In this study, hormonal birth control includes:

• a pill containing estrogen and progestin
• a pill containing progestin only
• a progestin injection
• a progestin implant
• a progestin-releasing intra-uterine device (IUD)

Researchers looked at recent birth control use among almost 10,000 people who were diagnosed with breast cancer under the age of 50. These people were compared to almost 20,000 other people without breast cancer (controls). The controls were close to the same age, had no history of breast cancer and were patients of the same general practice.

The researchers also looked at prior studies. Some of these included participants in a wider age range and only looked at the use of progestin-only birth control.

The key findings

• Current or recent use of birth control with either combined birth control (estrogen and progestin) or progestin alone leads to a small increase in breast cancer risk.
  • For example, the risk of breast cancer in women ages 35-39 who took either combined birth control or progestin alone birth control increased from 2% to 2.2% in the 15 years including and after birth control use.
• The increased risk for breast cancer quickly declines after stopping progestin-only birth control, as it does with the use of combined birth control. 
• The increase in risk was similar across birth control methods (pills, shots, implants or IUDs).

What does this mean for me?

If you have an average risk for breast cancer and you already use or are thinking about using hormonal birth control, understand that it may slightly increase your breast cancer risk while you take it and for a short time after you stop taking it.  

When you talk with your doctor about birth control, weigh the risks and benefits of your options. Consider your age and other risk factors. Hormonal birth control has many benefits. It is very effective and is known to reduce the risk of some health issues, including certain gynecologic cancers. It does not, however, protect against sexually transmitted diseases.

Another form of progestin-containing birth control will be available soon. Recently the FDA approved a progestin-based over-the-counter birth control pill - the OPill. This is expected to be available in early 2024 according to its manufacturer. Read the FDA approval here.

Reference

Fitzpatrick D, Pirie K, Reeves G, et al., Combined and progestogen-only hormonal contraceptives and breast cancer risk: A UK nested case-control study and meta-analysis. PLOS Medicine; 2023; 20(3). Published online March 21, 2023

Disclosure: FORCE receives funding from industry sponsors, including companies that manufacture cancer drugs, tests and devices. All XRAYS articles are written independently of any sponsor and are reviewed by members of our Scientific Advisory Board prior to publication to assure scientific integrity.

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posted 7/10/2023

Strengths and limitations

This research had some strengths and limitations. 

Strengths

• This study included data from a very large number of people.
• Prescription information came from the medical record, rather than people’s memories.

Limitations

• Because the information used for each person was from a specific period of time, rather than a complete prescription history, researchers could not determine how long birth control was used. They could only draw limited conclusions about long-term risk.
• Some of the other studies included in this research relied on people’s memories of using birth control after they were diagnosed with breast cancer.
• This study did not look at other risk factors for breast cancer—including genetics, family history or lifestyle. Therefore, the conclusions from this study may not apply to women at high risk for breast cancer due to an inherited mutation, family history or other factors.
• Although this study looked at research from around the world, most of the data was provided by studies of individuals from countries where people have a higher income and greater access to medical care.