Does Birth Control Increase Your Breast Cancer Risk?

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A recent study that links birth control use to an increased breast cancer risk caused a stir when news outlets splashed the findings across front pages without adequate context. The study, published in this month’s Cancer Research suggests that using certain types of birth control pills within the last year can almost triple the risk of breast cancer. That’s a scary statistic to anyone on the pill.

But don’t ditch your birth control just yet. We explain how the findings are much more nuanced than sensationalized headlines would suggest.

What the Study Found

The scientists at the Fred Hutchinson Cancer Research Center and the University of Washington in Seattle who conducted the research examined the pharmaceutical records of 1,102 women with breast cancer. The women on low-dose pills (about 20 micrograms of ethinyl estradiol) had no increased risk of breast cancer. However, those who had recently taken high-dose estrogen pills (50 micrograms of ethinyl estradiol or 80 micrograms of mestranol) were 2.7 times more likely to have breast cancer, and those who took moderate-dosed pills (30 to 35 micrograms of ethinyl estradiol or 50 micrograms of mestranol) were 1.6 times more likely.

What the Findings Really Mean

Though the numbers are shocking, it’s important to contextualize the study’s findings. For starters, high-dose estrogen pills are rarely prescribed. According to The Atlantic, only half of one percent of women were using the high-dose pills by the final phase of the study, which occurred between 2005 and 2009.

Additionally, the risk of developing breast cancer is actually quite low—there’s only a 1.5 percent chance of developing it at age 40, and a 2.38 percent chance at age 50. Increasing those odds, even by a factor of 2.7, still doesn’t mean the disease is likely to develop.

Finally, the elevated risk actually returned to a normal level after the women stopped using birth control pills—the increased risk only pertained to those who had taken the moderate- or high-dose pill within the past year.

What About IUDs?

Earlier last month, a different study in the journal of Obstetrics and Gynecology found that the levonorgestrel-releasing intrauterine system (LNG-IUS) or progesterone-releasing intrauterine device (IUD), may be associated with an increased risk of breast cancer as well. But like many other studies, the results indicated an association, not causation, and the actual total number of additional cases turned out to be quite small.

What It Means for Birth Control Prescriptions

“This new study has little to no impact on what we currently do in practice,” says One Medical’s Malcolm Thaler, MD. “The increased risk was only seen with high-dose pills, and the numbers were so small it is hard to draw any firm conclusions. Today, we almost always prescribe low-dose oral contraceptives, which the study found conveyed no increased risk at all.”

One Medical’s Kyoko Pena-Robles, MD, agrees, adding that in the absence of a family history of cancer, commonly-prescribed birth control pills are generally safe. “I have yet to recommend against the use of combined oral contraceptives. I, of course, would take a positive cancer history into consideration during counseling, especially if a patient has a personal history of estrogen receptor-positive breast cancer. However, in light of this supporting data, this reassures my current approach.”

As for the IUD, women should not let last month’s study influence their choices. “The researchers need more evidence to weed out confounding factors that may have contributed to the results,” Pena-Robles says. “This study has little merit until a more general population of LNG-IUS users is studied.”

For most women who take birth control, the benefits far outweigh the risks. Women taking the commonly prescribed low-dose pills shouldn’t let the study’s findings influence their current regimens, and women taking higher-dose pills should talk to their healthcare providers if they have concerns or questions.

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The One Medical blog is published by One Medical, an innovative primary care practice with offices in Boston, Chicago, Los Angeles, New York, Phoenix, the San Francisco Bay Area, Seattle, and Washington, DC.

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