What to know about contraceptives, breast cancer risk, and ‘informed choice’

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Denver Newsroom, Mar 23, 2023 / 13:48 pm (CNA).

Some forms of contraceptive use have “a significant increase in risk of breast cancer,” a new study says, and one fertility specialist believes that women deserve to know the risks — and the alternatives.

“If it increases risk, women simply need to be informed of this. They need to be able to make an informed choice,” Dr. Marguerite Duane, MD, a family physician who specializes in women’s health and restorative and reproductive medicine, told CNA.

“Without birth control, their risk is lower. It is lower, and that is a fact,” she said. Some women may choose to take that risk, while other women with risk factors like a family history of breast cancer may choose not to.

Duane is an adjunct associate professor at both Georgetown University and Duquesne University School of Medicine. She is also executive director of the Fertility Appreciation Collaborative to Teach the Science, a group of physicians, health care professionals, and educators who provide information on natural or fertility awareness-based methods of family planning.

She responded to news coverage of a study published in the PLOS Medicine journal by Oxford researchers. The study shows a 20% to 30% relative risk for breast cancer associated with progestogen-only contraceptives, according to CNN. The study drew on data from almost 10,000 U.K. women who were diagnosed with invasive breast cancer over a 21-year period and from more than 18,000 women who were not diagnosed with breast cancer.

Progestogens, also known as progestin, are synthetic hormone drugs that mimic progesterone, a natural hormone vital for menstruation and pregnancy. Progestogen-only contraceptives are provided in various ways: an implant, a hormonal intrauterine device, a contraceptive injection, or the “minipill.”

These contraceptives differ from the most popular contraceptive, a combined oral contraceptive pill that includes estrogen.

The researchers used data from the Clinical Practice Research Datalink and combined these results with previous research on contraceptives, CNN reported. They estimated “absolute excess risks,” which means “the additional number of women who would be expected to develop breast cancer in those who used oral contraceptives compared to those who did not,” according to the March 21 news release from Oxford Population Health’s Cancer Epidemiology Unit.

They reported “a significant increase in risk of breast cancer” regardless of which contraceptive drug was used.

In high-income countries, five years of use of combined or progestogen-only contraceptives has a 15-year “excess risk” of breast cancer dependent on age, according to researchers. They estimated that for women ages 16 to 20, this excess risk means 8 in 100,000 contraceptive users will develop breast cancer, while for women aged 35 to 39 it is 265 per 100,000 users.

“This, I think, further supports the argument that there are risks associated with hormonal birth control,” Duane told CNA. “Cancer is just one of the risks. There is also a significant risk of blood clots that can lead to stroke and heart attack in women. And I will tell you, I have personally met families who have buried their daughters due to the side effects of hormonal birth control, who felt anger and frustration that they were never informed.”

Any evaluation of the elevated relative risk of breast cancer should be based on each woman’s “baseline risk,” according to Duane.

“I do not have a family history of breast cancer. So I have a lower baseline risk. I also breastfed my children for nearly 10 years. Breastfeeding is a known factor that reduces a woman's risk,” she said. “For example, I might have a risk of breast cancer of 1%, whereas a person who has a strong family history and who also smokes, which is a known risk factor for breast cancer, might have a 10% risk of breast cancer.”

A 30% risk increase for Duane might mean a risk of breast cancer rising from 1% to 1.3%, whereas another woman could see a risk increase from 10% to 13%.

While birth control proponents will argue that contraceptives are safer than pregnancy, Duane said that just because someone is not on birth control does not mean that she will be pregnant. Duane herself has been pregnant for 36 months out of 30 years in which she has not used birth control.

Kirstin Pirie, a researcher at the University of Oxford, was the lead author of the progestogen-only contraceptive study. She told CNN that excess risks must be seen in light of the “well-established benefits” of contraceptive use for women of reproductive age, including birth control and hormone regulation.

Duane objected to this description.

“Pregnancy is not a disease, and the purpose of birth control is to prevent pregnancy. So hormonal birth control is synthetic steroid hormones that are given to healthy women to essentially create a diseased state, to make them infertile,” she said. “It does not regulate hormones; to be very clear, it suppresses normal hormone production.”

“The World Health Organization [WHO] recognizes hormonal birth control, specifically combination hormonal birth control, as a class one carcinogen. It is in the same category of cancer risk as tobacco, and asbestos,” she said. “And yet, it is considered a preventive health service that should be provided for free, again, to prevent pregnancy, which itself is not a disease.”

WHO’s International Association for Research of Cancer on its website lists estrogen-progestogen oral contraceptives as among 122 carcinogenic agents. It also notes “convincing evidence” that the drug has a “a protective effect against cancer in the endometrium and ovary.”

“Natural methods of family planning or fertility awareness-based methods can be used and can be used very effectively with effectiveness rates comparable to hormonal birth control. I think that’s really important,” Duane said. “The World Health Organization recognizes fertility awareness-based methods as the only form of family planning with no medical side effects.”

Catholic ethics rejects the use of contraceptives.

John F. Brehany, executive vice president of the National Catholic Bioethics Council, warned that Catholics should not adopt a “contraceptive mentality.”

“We should understand and respect the fertility of our bodies through the lens of faith — knowing that we are part of a created order designed by the God of love and life,” Brehany told CNA. “Life and sex are best approached within God’s plan (and using medicine and technology consistent with that plan), not as a series of risk mitigation calculations.”