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Sex

Hormonal birth control and cancer risk: reproductive cancers

There is a lot of discussion about birth control and cancer. Here’s what you should know.

by Maegan Boutot, Former Science Writer for Clue
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Top things to know

  • Prior to menopause, overall risk of reproductive cancers—breast, cervical, endometrial, and ovarian—is very low.
  • Use of estrogen-containing oral contraceptives (“the pill”) increases the risk of breast cancer and cervical cancer, but the risk of these cancers is still very low among pill users.
  • The pill decreases the risk of endometrial and ovarian cancer.
  • Other forms of hormonal birth control—like the IUD and injection—have not been studied as much as the pill.

There has been a lot of press within the last few years about the association between hormonal birth control and breast cancer. Some people may be nervous about using hormonal birth control due to this reason.

If you’re interested in using hormonal birth control, it’s important to consider not only the potential harms—like the potential increased risk of some cancers—but also the demonstrated benefits of using hormonal birth control—like the decreased risk of unintended pregnancy—before deciding which method is right for you.

In this guide, we talk about how hormonal birth control increases and decreases the risk of certain cancers.

Most of the information we have is about estrogen-containing pills. This is because estrogen-containing pills were the first form of hormonal contraception to be offered, and because many people use this method, we have lots of data.

There is far less information on progestin-only methods, like the hormonal intrauterine device (IUD), the progestin-only shot (eg. DMPA), or the implant. These methods are relatively new and fewer people use them, so there’s less information on them. Cancer is very rare among people who haven’t reached menopause. If you have only a few people using a method, you’re unlikely to have enough people with cancer diagnoses to do any statistical analyses. We try to provide information where we can.

What your healthcare provider might say

Hormonal birth control probably increases the risk of breast cancer and cervical cancer. In contrast, hormonal birth control decreases the risk of endometrial and ovarian cancer.

Major medical associations do not think that the risk of breast cancer or cervical cancer outweighs the benefits of using birth control for most people (1). Pregnancy, particularly unintended pregnancy, also carries health risks, so it’s important to consider your health priorities and your personal risk of developing certain conditions.

Here’s why it’s tricky

Below we explain some of the relative risks in the development of cancer, but hormonal birth control won’t affect everybody’s personal risk of cancer in the same way.

Some people are at very low risks of some cancers, such that a net increase or decrease in their risk probably won’t mean much. Other people are at higher risk of some cancers, and so an increase or decrease in the likelihood of developing cancer may be more important to them.

Hormonal birth control may not be a good fit for some people due to their higher-than-average personal risk of cancer.

  • People who have breast cancer or recently had breast cancer should probably not use any hormonal method of birth control (1). This includes both an estrogen-containing method like the pill and progestin-only methods like the hormonal IUD.
  • People who have immediate family members who have had breast cancer are also at increased risk of breast cancer (2) and may want to consider if they are comfortable adding a potentially small increase in risk from hormonal birth control. However, despite this increased personal risk, people with a family history of breast cancer can still use hormonal birth control—even estrogen-containing methods (1). The United States Centers for Disease Control and Prevention (1) does not consider a family history of breast cancer to be a reason to discourage use (1).

In contrast, some groups of people are at increased risk of endometrial and ovarian cancer. There is a link between using hormonal birth control and decreased risk of these cancers. Although not as common as breast cancer, uterine cancer (of which endometrial cancer is a type) is the fourth most common cancer in US women, and ovarian cancer is the 10th most common (3).

  • People with polycystic ovary syndrome (PCOS) are more than two times as likely to develop endometrial cancer (4) .
  • For people with PCOS, hormonal birth control may provide multiple benefits, such as management of their condition and decreased risk of cancer. Since everyone is different, you should speak to your healthcare provider about your personal risk of developing cancer when using and not using hormonal birth control.

Here’s the current state of research

Birth control and breast cancer

Both estrogen-containing birth control methods and progestin-only methods have been associated with increased risk of breast cancer (5-9).

In one large study published in 2017, which included all women in Denmark, it was found that people who were currently using or recently used any form of hormonal birth control were, on average as a group, about 20% more likely to be diagnosed with breast cancer as compared to people who were not using hormonal contraceptives (5).

The risk of a particular method is not necessarily 20% though. Some hormonal methods had higher risk, and some had lower. For example, this study found there was no increase in risk among implant-users or users of the progestin-only shot (5), but we need more research to confirm these results.

The association between estrogen-containing pills and breast cancer has been studied the most. The risk of breast cancer diagnosis has been found to be 20% higher among current or recent users of the pill as compared to non-users of any hormonal birth control (5-7).

The specific formulation of the pill, such as the amount of estrogen and the type of progestin, may play a role in the risk of developing breast cancer, but more research is needed (5).

Another large study suggests that current and recent users of hormonal methods are about 50% more likely to be diagnosed (8) but many of the participants in this study were using methods that had higher amounts of estrogen than most methods being used today. Although this study was published in 2017, the data were collected between 1968 and 1996, with most participants probably using birth control formulations that were on the market in the 1960s through the 1980s (8).

Two studies have found that the hormonal IUD also increases risk by about 20% (5,9).

The increase in the risk of breast cancer appears to be highest while people are currently using hormonal birth control, and appears to decrease over time after people stop using their hormonal method (5-8).

People who used hormonal birth control for many years may also be at an increased risk of breast cancer, compared to people who used it for less time. A meta-analysis, which is a type of study that re-analyzes data from many studies, found that duration of use was not associated with increased risk (7); however, a larger, more recent study using the population of Denmark found that duration of use was associated (5). This association had a very clear trend (5).

What to keep in mind when looking at research on hormonal birth control and cancer

There are a few important things to keep in mind when reading these results.

  1. Most people using hormonal birth control are at very low personal risk of breast cancer, so a 20% increase in risk does not mean a person’s overall risk is high. In the United States about 60 out of 100,000 women under 50 years old are diagnosed with breast cancer each year (10), though risk increases with age. Less than 2 in 100,000 American women ages 20-24 are diagnosed with breast cancer annually (10), whereas about 250 out of 100,000 American women age 45-49 are (10).
  2. These studies looked at breast cancer diagnoses, not breast cancer occurrence. It’s possible that people who use hormonal birth control are more likely to get screened for breast cancer, compared to people who do not use hormonal birth control—though not all researchers think this would explain the results (5,6,8).
  3. There are things a person can do to reduce their overall risk of breast cancer, such as reducing alcohol consumption and exercising (2). Engaging in healthy behaviors, even while using hormonal birth control, can help you lower your overall risk of developing breast cancer.

Birth control and cervical cancer

Use of estrogen-containing pills may increase the risk of cervical cancer (7,8,11,12). Studies do not agree on the size of the increase, or if the increase is statistically significant. Cervical cancer risk may be higher among people who have used pills for 5 or more years (7,8,11,12). The increase in risk disappears over time after discontinuation (8,11,12).

One study found that the progestin-only contraceptive shot increased risk of cervical cancer (12), but more studies are needed.

It is important to remember that cervical cancer is preventable, even among people using hormonal birth control. Almost all cervical cancer cases are caused by human papillomavirus (HPV), which is a sexually transmitted infection (7,13). If a person does not get HPV, then they are very, very unlikely to develop cervical cancer, even if they are using hormonal birth control.

Getting the HPV vaccine and using condoms, especially if you have sex with multiple partners, can prevent HPV transmission and, therefore, cervical cancer (13).

Birth control and endometrial cancer

Use of some forms of hormonal birth control decrease the risk of endometrial cancer.

Current users of estrogen-containing pills have half as much risk (50%) as those who never used hormonal methods (8,14,15). Former-users of the pill also have a reduced risk after discontinuation (8,14).

There has been less research on progestin-only birth control, but some studies have found reduced risks too. One study from 2014 found that people with heavy menstrual bleeding who used the hormonal IUD had half the risk of developing endometrial cancer (9). Users of the progestin-only shot have been found to be at reduced risk (16,17,19), and progestin-only pills might also reduce risk (17,18), though more research is needed.

Theoretically, users of progestin-only methods should be at a reduced risk, because it is thought that the synthetic progestins prevent the development of endometrial cancer (17,20).

The hormonal IUD and an oral form of the progestin found in the contraceptive shot have actually been used to treat some forms of endometrial cancer and endometrial hyperplasia, or abnormal cell growth (20,21).

Birth control and ovarian cancer

Use of hormonal birth control decreases the risk of ovarian cancer (8,9,22-26). Hormonal birth control is thought to reduce the risk of ovarian cancer by suppressing ovulation (27). The process of ovulation causes damage to the ovaries (27), which, over time, can cause the development of cancer.

Combined-hormonal methods—like the pill, patch, and ring—have consistently been shown to decrease risk (8,22,23). Progestin-only methods—like the contraceptive shot, hormonal IUD, and implant—are generally found to decrease risk (9,26), though one study found that this decrease was not statistically significant (23).

As with endometrial cancer, current users of hormonal contraception had the greatest reduction in risk, but former users may also be less likely to develop ovarian cancer for years after discontinuation (8,23-25). People who use hormonal birth control for multiple years appear to benefit more than people who use these methods for less time (19,23-26).

Behaviors or life events that prevent ovulation, like use of some hormonal birth control methods, pregnancy, and breastfeeding, are associated with a decrease in the risk of ovarian cancer (19,26,27).

This theory may also explain why combined hormonal birth control methods are more likely to show a significant association than progestin-only methods. Combined hormonal methods prevent pregnancy primarily by suppressing ovulation (19). Progestin-only methods sometimes suppress ovulation, but it depends on the type of method—and sometimes on the person (19). For example, the contraceptive injection ("the shot") prevents pregnancy by suppressing ovulation, whereas the hormonal IUD primarily prevents pregnancy through thickening cervical mucus and interacting with sperm function (19). This may be why studies don’t always agree on the size of the reduction in risk of progestin-only methods.

Clue can help you track your menstrual cycle characteristics and the changes in your body over the course of your cycle, which may be helpful in assessing if hormonal birth control is right for you.

Download Clue to track your menstrual cycle and birth control use

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