‘Small Increase’ in Breast Cancer With Levonorgestrel IUD?

TOPLINE: 
The use of a levonorgestrel-releasing intrauterine system (LNG-IUS) is associated with an increased risk for breast cancer. An analysis by Danish researchers found 14 extra cases of breast cancer per 10,000 women using this type of an intrauterine device (IUD) vs women not using hormonal contraceptives.
METHODOLOGY:
The investigators used nationwide registries in Denmark to identify all women aged 15-49 years who were first-time initiators of any LNG-IUS between 2000 and 2019.
They matched 78,595 new users of LNG-IUS 1:1 with women with the same birth year who were not taking hormonal contraceptives.
Participants were followed through 2022 or until a diagnosis of breast cancer or another malignancy, pregnancy, the initiation of postmenopausal hormone therapy, emigration, or death.
The investigators used a Cox proportional hazards model to examine the association between the continuous use of LNG-IUS and breast cancer. Their analysis adjusted for variables such as the duration of previous hormonal contraception, fertility drugs, parity, age at first delivery, polycystic ovarian syndrome, endometriosis, and education.
TAKEAWAY:
Compared with the nonuse of hormonal contraceptives, the continuous use of LNG-IUS was associated with a hazard ratio for breast cancer of 1.4 (95% CI, 1.2-1.5).
The use of a levonorgestrel IUD for 5 years or less was associated with a hazard ratio of 1.3 (95% CI, 1.1-1.5). With 5-10 years of use, the hazard ratio was 1.4 (95% CI, 1.1-1.7). And with 10-15 years of use, the hazard ratio was 1.8 (95% CI, 1.2-2.6). A test for trend was not significant, however, and “risk did not increase with duration of use,” the study authors wrote.
IN PRACTICE:
“Women should be aware that most types of hormonal contraceptive are associated with a small increased risk of breast cancer. This study adds another type of hormonal contraceptive to that list,” Amy Berrington de Gonzalez, DPhil, professor of clinical cancer epidemiology at The Institute of Cancer Research in London, England, said in comments on the research. “That has to be considered with the many benefits from hormonal contraceptives.”
Behaviors such as smoking could have differed between the groups in the study, and it has not been established that LNG-IUS use directly causes an increased risk for breast cancer, said Channa Jayasena, PhD, an endocrinologist at Imperial College London, London, England.
“Smoking, alcohol and obesity are much more important risk factors for breast cancer than contraceptive medications,” he said. “My advice for women is that breast cancer risk caused by LNG-IUS is not established but warrants a closer look.”
SOURCE:
Lina Steinrud Mørch, MSc, PhD, with the Danish Cancer Institute in Copenhagen, Denmark, was the corresponding author of the study. The researchers published their findings online on October 16 in JAMA.
LIMITATIONS: 
Unmeasured confounding was possible, and the lack of a significant dose-response relationship “could indicate low statistical precision or no causal association,” the researchers noted.
DISCLOSURES:
The study was funded by Sundhedsdonationer.
This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.
 
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