The use of a common hormonal intra-uterine device for contraception is linked to a slightly elevated risk of breast cancer, a recent study revealed.

The researchers have found that Levonorgestrel-Releasing Intrauterine Systems (LNG-IUS) was linked to 14 extra cases of breast cancer per 10,000 women compared to those not using contraceptive medication in a study group of participants between the ages 15 and 49. However, the risk did not increase with the duration of use.

LNG-IUS contains the female hormone, levonorgestrel which when placed in the uterus slowly releases the hormone to prevent pregnancy. It is sold under Skyla, Kyleena, Liletta, and Mirena.

The researchers used data from Danish registers involving 78,595 women, with an average age of 38, who began using a levonorgestrel-releasing intrauterine system (at doses of 52 mg, 19.5 mg, and 13.5 mg) between 2000 and 2019. This study group was matched with nonusers of hormonal contraceptives. All participants were tracked until they were diagnosed with breast cancer or other cancers, became pregnant, began postmenopausal hormone therapy, emigrated, died, or until December 2022.

After an average follow-up period of 6.8 years, 1,617 participants were diagnosed with breast cancer, including 720 users of the intrauterine system.

"Although the absolute breast cancer risk is low in young women, this study found an excess risk of 14 per 10,000 females," a news release stated.

The study did not note how the risk compares with oral contraceptive pills. The findings were published in Jama Network Open.

According to Dr. Channa Jayasena, Reader in Reproductive Endocrinology, Imperial College London, who was not involved in the study, the findings were "highly unexpected". "We have always assumed that the LNG-IUS would not increase breast cancer risk due to the much lower levels of hormone exposure to the whole body. The results of this study are therefore highly unexpected," Dr. Jayasena said.

However, Dr. Jayasena noted that while the study attempted to match the two groups of women by factors like age, weight, and education, certain behaviors such as smoking were not accounted for. This could make the non-contraceptive group look healthier in comparison to the LNG-IUS group. "It is important that smoking, alcohol and obesity are much more important risk factors for breast cancer than contraceptive medications," Dr. Jayasena said.

Another expert, Dr. Mangesh Thorat, Consultant Breast Surgeon, at Homerton University Hospital, pointed out that although there is a small increase in the risk of breast cancer associated with hormonal forms of contraception, there is broad consensus among the medical fraternity that the overall benefits of hormonal contraception outweigh the harms.

"Furthermore, as the baseline risk of breast cancer is lower in younger individuals, any increase in the risk associated with the use of hormonal coil is also smaller. The risk increases with increasing age and it is reasonable for women near 40 years of age to have a discussion with their healthcare practitioner regarding non-hormonal modes of contraception," Dr. Thorat said.

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