A UVA Heart & Vascular Center Initiative

Setting the Record Straight: The Link Between Breast Cancer and Oral Contraceptives

Posted December 19, 2017

If you are one of the millions of women using hormonal contraceptives, recent headlines may have caused you to rethink your birth control. But … before you abandon the Pill or trade in your IUD, be sure to do a little bit of legwork and get the whole story. To jumpstart your research, we spoke to University of Virginia Cancer Center oncologist Patrick Dillon, MD, about the recent study findings that put this topic back in the spotlight.

Is it true that doctors have known for some time that hormonal contraceptives increase a woman’s risk of developing breast cancer?
Yes, there were three historical studies prior to the most recent one, which appeared in the New England Journal of Medicine earlier this month. The important thing to note with all of these studies, including the one that just came out of Denmark, is that they were observational studies, not prospective randomized studies, so they do not show cause and effect.

How is this study different from those done in previous years?
Namely, the formulations of hormonal therapies have changed compared with contraceptives used in the past. There are new progestins used and lower doses of estrogen, so the hope was that the breast cancer risk would be lower with newer hormonal contraceptives, but the exact same breast cancer risks were observed in this newer study. So this study really is not expected to be practice changing.

What were the results of the study?
The study revealed that women who were using or had used hormonal contraceptives had a 20 percent higher relative risk of developing breast cancer compared to those who never used them. This included women using birth control pills and intrauterine devices (IUDs) that release hormones.

Twenty percent seems significant.
This is a relative risk increase, which means a comparison. It does not mean that a woman taking hormonal contraceptives has a 20 percent risk of breast cancer. In fact, in this study there were only 13 additional breast cancers per 100,000 patients. That’s a pretty low risk. In women under the age of 35, there were just two additional cases per 100,000 women. Overall, this results in one extra breast cancer diagnosed for every 7,690 women using hormonal contraception for one year. And some of these women had other risk factors for breast cancer that weren’t accounted for. They may have been obese or had a family history of breast cancer – we are unable to account for these cofactors in this study.

What is the takeaway from these study findings?
This study is a good reminder that it’s important to be aware of the risks of all medications. Hormonal contraceptives do raise your risk for breast cancer slightly. They also increase the risk of blood clots for women who smoke. But keep in mind that there are benefits to these drugs as well, so you have to weigh the pros and cons.

Contraceptives have been shown to lower a woman’s risk for endometrial, ovarian and colon cancers. They also have advantages for women with menorrhagia or painful, heavy periods, and mood issues. Indeed, the rates of hysterectomy done for reasons of uncontrollable bleeding have substantially dropped since the inception of hormonal contraception and innumerable lives have been saved because of this. In many cases, the benefits far outweigh the risks. Women should talk to their doctor about their personal risk factors and health concerns before deciding on a contraceptive. Those women who are already at an increased risk for breast cancer may want to choose an alternative birth control method. It’s a personal decision and women should be sure they have done their research.


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