Mirena IUD Side Effects May Increase Risk of Breast Cancer: Study

New research suggests that side effects of IUD birth control implants, such as Mirena and Skyla, which release the progestin levonorgestrel, may increase the risk of breast cancer.

Mirena and Skyla are intrauterine devices (IUD), sometimes referred to as intrauterine systems (IUS), which are implanted into the uterus to provide long-term birth control protection against pregnancy.

In a study published ahead of print in the medical journal Obstetrics & Gynecology, Finnish researchers report that while levonorgestrel-releasing IUDs do appear to protect against some types of malformations and other cancers, women who receive the implants to treat heavy periods may face a greater risk of breast cancer.

Researchers looked at data on women from ages 30 to 49, who used levonorgestrel-releasing intrauterine systems (LNG-IUS) from 1994 to 2007

for menorrhagia, which involves an abnormally heavy and prolonged menstrual period at regular intervals. The data was collected from the National Reimbursement Registry and the Finnish Cancer Registry.

In the U.S., Bayer sells both of the LNG-IUS systems on the market, the Mirena IUD and the Skyla IUD. Levonorgestrel is a second-generation progestin commonly used in birth control products, including many birth control pills.

The study found 2,781 cases of cancer among women using a levonorgestrel IUD. For most cases, the rate of cancer dropped significantly when a woman used a LNG-IUS. Cases of endometrial adenocarcinoma were cut in half, and there were only 60% of the expected cases of ovarian cancer. Pancreatic cancer rates were also cut in half by women using a LNG-IUS, and rates of lung cancer dropped 32%.

However, researchers saw a nearly 20% increase in the risk of breast cancer with levonorgestrel IUDs. Based on the rate among the general population, researchers expected to find 1,292 breast cancer cases, instead they found 1,542.

“The levonorgestrel-releasing intrauterine system may have a protective effect against endometrial malignant transformation. Using the levonorgestrel-releasing intrauterine system for treatment of menorrhagia during reproductive years was associated with a lower incidence of endometrial, ovarian, pancreatic, and lung cancers than expected,” the researchers concluded. “Levonorgestrel-releasing intrauterine system use was associated with a higher than expected incidence of breast cancer.”

Mirena IUD Problems

Mirena is the best selling IUD in the United States. However, only a few variations of the long-term birth control implants are on the market, including Mirena and Skyla, as well as the ParaGard, which does not release levonorgestrel.

Bayer currently faces several thousand Mirena lawsuits, involving allegations that the drug maker failed to adequately warn about potential side effects of the IUD birth control. Most of the cases involve women who suffered severe internal injuries after Mirena IUD migrated out of place, resulting in perforations of the uterus and other complications.

Bayer has maintained that it intends to defend the migration injury cases, arguing that information about the risk of perforation was included on the warnings provided with the IUD. However, plaintiffs in that litigation maintain that the previous warnings were vague and misleading, suggesting that the risk of injury only exists at the time of insertion. Most of the complaints involve women who found that the Mirena migrated spontaneously, often long after the IUD was successfully placed in the uterus.

In the federal court system and New Jersey state court, coordinated proceedings have been established, centralizing the cases before one judge to avoid conflicting pretrial rulings, duplicative discovery and to serve the convenience of the parties, witnesses and the courts.

Given the similar factual allegations raised in the cases, a series of Mirena bellwether trials are expected to begin in the second half of 2015, designed to help the parties gauge how juries may respond to certain evidence and testimony that is likely to be repeated throughout the litigation.

If Bayer continues to refuse to make any Mirena settlement offers following a series of bellwether trials in the MDL, the drug maker could face hundreds of individual trials throughout the United States.