medwireNews: A Danish population-based study has found an association between use of levonorgestrel-releasing intrauterine systems (LNG-IUSs) and an increased risk for breast cancer.
“The risk did not increase with duration of use,” report Lina Steinrud Mørch and colleagues from The Danish Cancer Institute in Copenhagen in a research letter to JAMA.
They explain that while use of LNG-IUSs “has been increasing,” the relationship “with breast cancer risk remains unclear.”
The team therefore drew on nationwide Danish registers to identify all women aged 15–49 years who initiated any LNG-IUS at doses of 52.0, 19.5, or 13.5 mg between 2000 and 2019, excluding those who had used any other hormonal contraceptives within 5 years prior to starting the LNG-IUS, as well as those with a history of postmenopausal hormone therapy or cancer.
A total of 78,595 new users were matched by birth year to the same number of nonusers of hormonal contraceptives. Over a mean follow-up of 6.8 years, 1617 participants received a breast cancer diagnosis.
Compared with nonuse of hormonal contraceptives, use of LNG-IUSs was associated with an increased risk for breast cancer, with a hazard ratio (HR) of 1.4.
Analysis by duration of use of LNG-IUSs gave HRs for breast cancer of 1.3 for 0–5 years, 1.4 for more than 5 to 10 years, and 1.8 for more than 10 to 15 years, equating to an excess of 14, 29, and 71 breast cancer diagnoses per 10,000 users, respectively.
However, there were no statistically significant differences in risk between the different durations.
The researchers note that “[t]he HR with short-term LNG-IUS use was similar to that of contraceptive pills,” at 1.3 versus 1.2.
They conclude: “Given the increase in LNG-IUS use among females at an age with some risk for breast cancer, and its likely long-term use, information about breast cancer risk should accompany discussions about benefits and risks.”
Commenting on the findings to the press, Channa Jayasena (Imperial College London, UK) described the results as “highly unexpected,” adding that “[i]t is unfortunate that this study did not compare breast cancer risk between the LNG-IUS and oral contraceptive pill.”
He also highlighted that “smoking, alcohol and obesity are much more important risk factors for breast cancer than contraceptive medications.”
But Jayasena concluded: “We always need to be vigilant to new health risks from medical treatments, and this is no exception. My advice for women is that breast cancer risk caused by LNG-IUS is not established but warrants a closer look.”
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JAMA 2024; doi:10.1001/jama.2024.18575
