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Both progestin-only and combined hormonal contraceptives may increase the risk of breast cancer, a study finds. MYCHELE DANIAU/Getty Images
  • Progestin-only birth control pills are a common form of hormonal contraceptive, yet knowledge on their association with breast cancer risk was limited. In a new study, researchers investigated the link between hormonal contraceptive use and breast cancer risk.
  • They found that progestin-only contraceptive use increases breast cancer risk similarly to combined contraceptive use.
  • They say that physicians should weigh the benefits and risks to patients of hormonal contraceptive use. Experts say the findings are broadly in line with known risks, which overall are small.

Between 2017 and 2019, around 65% of women aged 15- 49 used some sort of contraception, and 14% of them used the pill. Contraceptive pills come in two forms: the progestin-only pill and the combined pill containing both progestin and estrogen-based ingredients.

Progestin, or progestogen, is a synthetic version of progesterone, a naturally occurring hormone.

A meta-analysis from 1996 found that people taking combined contraceptives have a slightly increased risk for breast cancer within 10 years of usage.

In recent years, progestin-only methods of contraception — including pills, injectables, implants, and intrauterine devices (IUDs) — have become more popular. In England, drug prescriptions increased from 1.9 million in 2010 to 3.3 million in 2020.

Until now, however, there has been limited research on the impact of progestin-only contraceptives on breast cancer risk.

Recently, researchers investigated the link between hormonal contraceptive use and break cancer risk.

Like combined pills, they found that progestin-only contraceptives slightly increase breast cancer risk.

The study was published in PLOS Medicine.

For the study, the researchers analyzed health records from a UK primary care database. They included data from 9,498 women aged under 50 years old with breast cancer and 18,171 women without.

Altogether, 44% of women with breast cancer and 39% of those without had a prescription for hormonal contraceptives. About half of these were for progestin-only preparations.

Ultimately, the researchers found that combined contraceptive pill use increased breast cancer risk by 23%.

They also found that oral progestin-only contraceptive pills increased breast cancer risk by 29%.

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Other progestin-only formulations, including injectables, implants, and intrauterine devices (IUDs), increased breast cancer risk by 18%, 28%, and 21%, respectively.

The researchers added that five years of oral contraceptive use was linked to breast cancer incidence in 8 per 100,000 users aged 16 to 20 years old and an incidence of 265 per 100,000 users aged 35- 39 years old.

Dr. Irene M. Kang, medical director of women’s health medical oncology at City of Hope Orange County, not involved in the study, told Medical News Today:

“All medications have risks and benefits, which is why discussing concerns with your provider is essential. Negative effects of oral contraceptives include strokes, heart attacks and blood clots. Research has shown that oral contraceptives can impact an individual’s risk of certain types of cancer – in some cases upwards, and in some cases, such as ovarian and endometrial cancers, downwards – through changing the levels of estrogen and progesterone. Additional benefits are family planning and more regulated menstrual cycles.”

Dr. Lilian Harris, a medical oncologist at Novant Health Cancer Institute, not involved in the study, agreed that hormonal contraceptives have risks and benefits:

“For example, they can protect against pelvic inflammatory disease and help with menstrual pain, […] fibroids, endometriosis and acne. They have also been shown to decrease the risk of […] uterine cancers. Conversely, there are also potential risks with any medication. For oral contraceptives, these risks can range from nausea, headaches, and breast tenderness to […] increased risk for breast cancer.”

The researchers concluded that current or recent progestin-only contraceptives are linked to a slight increase in breast cancer risk.

They say that such risks must be balanced against the benefits of contraceptives in childbearing years.

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When asked about the study’s limitations, Dr. Kang noted that due to the study design, it only explains short-term risk associations as opposed to long-term risk.

Dr. Kristina Shaffer, breast surgical oncologist at Novant Health Cancer Institute, not involved in the study, also told MNT:

“In addition, the study included premenopausal women, an age group where breast cancer incidence is lower, meaning that other factors may have been driving the slightly higher risk demonstrated in the study. For example, while the study did account for some of the factors known to be related to breast cancer risk, it did not account for family history, genetic predisposition, or history of atypical breast cells which are well-established to impact breast cancer risk.”

MNT also spoke with Dr. Parvin Peddi, board certified medical oncologist and director of Breast Medical Oncology for the Margie Petersen Breast Center at Providence Saint John’s Health Center and Associate Professor of Medical Oncology at Saint John’s Cancer Institute in Santa Monica, CA, not involved in the study.

“[The] main take home message is that this study finds that women do not need to choose a progesterone only containing birth control medication because of perceived lower risk of birth cancer.”

– Dr. Peddie

“On the other hand, it’s important to note that the absolute increased risk of breast cancer from any of these medications is quite low and this study should not dissuade women from using hormone-containing birth controls,” Dr. Peddie explained. “Risk of breast cancer was seen in less than 0.5% of women age 35-39 years old due to use of these medications and in even fewer women who used these medications at a younger age.”

Dr. Schaffer agreed that while the increase in risk may sound high at 20-30%, it is relatively small.

“For instance, if the risk of a 30-year-old female developing breast cancer is 5%, then a relative increase of 20% would bring her risk to 6%. And this is why the study concludes that there is a slight increase in breast cancer risk,” she explained.

Dr. Kang also noted:

“As with all cancers, your breast cancer risk increases with age, and in this case, also with the length of time that hormonal contraceptives are used. If you are at a higher risk for breast cancer, switching to a hormone-free birth control may be a more beneficial option for you. If you are diagnosed with breast cancer, seek care from an expert who specializes in your type of cancer.”

“Finding breast cancer early is one of the most important factors in successful treatment of this disease — and that’s why self-exams and screenings are so vital,” Dr. Kang concluded.