From the Guidelines
The use of levonorgestrel-releasing intrauterine systems (LNG-IUS) may slightly increase the risk of breast cancer, but the overall risk remains low for most women, and the potential benefits often outweigh this risk. The risk of breast cancer in users of LNG-IUS appears to be slightly increased compared to non-hormonal contraceptive users, with a relative risk increase of approximately 1.2 to 1.4 times that of non-users, as suggested by a large epidemiological study 1. This risk is similar to that seen with other hormonal contraceptives and appears to diminish after discontinuation of the device. The LNG-IUS primarily works locally in the uterus, releasing much lower systemic hormone levels than oral contraceptives.
Some key points to consider:
- The potential benefits of the LNG-IUS, including highly effective contraception, reduced menstrual bleeding, and protection against endometrial cancer, often outweigh this small risk increase for many women 1.
- The slight increase in breast cancer risk is thought to be related to the hormonal effects of levonorgestrel, even at the lower systemic levels provided by the IUS, potentially promoting the growth of existing cancer cells rather than initiating new cancers.
- For women with a history of breast cancer, alternative non-hormonal contraception methods are recommended due to the potential risks associated with hormonal contraceptives 1.
- However, for women treated with tamoxifen, a levonorgestrel-containing intrauterine system (IUS) may be preferable since it has been shown to reduce tamoxifen-induced endometrial changes without increasing the risk of breast cancer recurrence 1.
In terms of morbidity, mortality, and quality of life, the benefits of using LNG-IUS often outweigh the potential risks for many women, especially those under 40 without additional risk factors. However, each woman's individual risk factors and medical history should be taken into account when deciding on a contraceptive method.
From the Research
Risk of Breast Cancer in Users of Levonorgestrel-Releasing Intrauterine Systems
- The risk of breast cancer in users of levonorgestrel-releasing intrauterine systems (LNG-IUS) has been studied in several research papers, with varying results 2, 3, 4, 5.
- A systematic review and meta-analysis published in 2020 found that LNG-IUS users have an increased breast cancer risk, with an odds ratio (OR) of 1.16 (95% CI 1.06-1.28) for all women, and an OR of 1.52 (95% CI 1.34-1.72) for women aged 50 years or older 2.
- Another study published in 2018 found that LNG-IUS use was associated with a decreased risk of ovarian and endometrial cancer, but no increased risk of breast cancer, with a relative risk (RR) of 1.03 (95% CI 0.91-1.17) for breast cancer 3.
- A nationwide cohort study published in 2016 found that LNG-IUS users had an increased risk of both ductal and lobular breast cancer, with a standardized incidence ratio (SIR) of 1.20 (95% CI 1.14-1.25) for ductal cancer and 1.33 (95% CI 1.20-1.46) for lobular cancer 4.
- A systematic review published in 2023 found that the results imply an increased breast cancer risk in LNG-IUS users, especially in postmenopausal women and with longer duration of use, but the heterogeneity of the analyzed studies and vast number of confounding factors call for further investigations 5.
- A study published in 2020 found that the combination of low-dose levonorgestrel intrauterine system with estrogen therapy gives less normal breast tissue proliferation than oral progestogens, which may have implications for breast cancer risk 6.
Factors Influencing Breast Cancer Risk
- Age: The risk of breast cancer may be higher in older women using LNG-IUS, with an OR of 1.52 (95% CI 1.34-1.72) for women aged 50 years or older 2.
- Duration of use: The risk of breast cancer may be higher with longer duration of LNG-IUS use, as found in the systematic review published in 2023 5.
- Type of cancer: The risk of breast cancer may vary by type of cancer, with an increased risk of both ductal and lobular cancer found in the nationwide cohort study published in 2016 4.
- Combination with estrogen therapy: The combination of low-dose levonorgestrel intrauterine system with estrogen therapy may give less normal breast tissue proliferation than oral progestogens, which may have implications for breast cancer risk 6.