For decades, studies have shown that estrogen-only birth control pills — synthetic female hormones — can slightly increase one’s chances of developing breast cancer. However, less research has been done on the risks associated with progestogen-only contraceptives such as intrauterine devices and the so-called mini-pill.
A study published in the journal PLOS Medical Tuesday found that breast cancer risk is the same for all these options, regardless of whether one or two hormones are used.
Women who used or had recently used hormonal IUDs, two-hormone combinations, or progestogen-only birth control pills were at a higher risk of developing breast cancer than women who didn’t.
According to the Centers for Disease Control and Prevention , 14% of U.S. females aged 15 to 49 used oral contraceptives, while 10% used long-acting reversible contraceptives like IUDs or birth controls implants.
Gillian Reeves co-authored the study and directs Cancer Epidemiology Unit, University of Oxford.
She said that hormonal contraceptives can have an increased risk, regardless of the type. “These newer types, which haven’t been as well studied, look no different.
These findings were based upon an analysis of prescription records of women aged 50 and under in the U.K. Close to 9,500 women were diagnosed with breast carcinoma between 1996-2017, while over 18,000 weren’t.
Researchers combined their findings with 12 other studies to assess the risk of progestogens-only contraceptives. Overall, the results were similar and suggest that hormonal contraception could increase breast cancer risk by as much as 30%.
This is relative risk, however: The average woman has a 1-in-8 chance of developing breast cancer at some point in her life, so the study suggests that hormonal birth control slightly ups those odds.
Reeves stated that among women aged 35-39, the additional risk will only be 0.2% over the 15-year period. This is still a small number.
Associate professor of obstetrics at the University of North Carolina School of Medicine Rachel Urrutia said that the new findings were consistent with similar studies. She also shared her 2013 analysis that showed that breast cancer rates were up to 8% when birth control pills included a combination of two hormones.
Urrutia, however, was not involved in the new research and said it was difficult to determine with certainty if hormonal contraception increases the risk of developing cancer without conducting a randomized controlled trial.
She said, “That’s going be difficult to do for contraceptives because it’s not always possible to find people willing to take birth control pills or to avoid them.”
She also suggested that there could be other factors that may have contributed to the higher risk of breast cancer in Reeves and other studies. Urrutia stated that a family history or diet of breast cancer could also impact risk. Reeves’ study didn’t adjust for these variables.
After stopping birth control, breast cancer risk may decline
Reeves’ analysis also included a Study from 2017, which similarly identified a 20% increase in breast cancer for women who used hormonal contraception.
The study tracked 1.8 million Danish women for more than 10 year. One additional case of breast carcinoma was found for every 7,690 women who used hormonal contraception during a given year. This is in comparison to the number of women who did not use hormonal contraception.
Reeves stated that breast cancer is hormone-sensitive. Estrogen or progesterone can activate hormone receptors within cancer cells. This may stimulate growth.
She said that any medication given to a woman to disrupt her menstrual cycle could change her exposure to both sex hormones and, in turn, increase her chance of developing hormonally sensitive cancers.
Reeves said that once someone stops using hormonal birthcontrol, the majority of research suggests that breast cancer risk gradually decreases.
She stated, “We wouldn’t have expected that use 10, 15, years ago would have much effect now.”
Urrutia stated that doctors need to do more research before they can give advice to patients about the effects of birth control on their cancer risk, even if they stop using it.
According to the National Cancer Institute , some studies have shown that hormonal contraception can reduce the risk of certain types of cancer. This list includes endometrial and ovarian cancers.
Reeves stated that “the protection against ovarian cancer and endometrial carcinoma is quite a bit stronger and lasts longer — it lasts until middle age when those cancers become more common — I would think that most women will find the benefits outweigh the risks of breast cancer.”
