My wife’s having a uterine coil fitted - as an oncologist should I be worried, in view of new research?

The research published in the prestigious journal Jama has discovered a link between progesterone containing intrauterine coils with breast cancer. Although it’s already known that taking a progesterone pill could increase the breast cancer risk, up until now, a link with intrauterine devices was not firmly established.

The major study, conducted in Denmark, involved over 150,000 women followed for five to 15 years. Researchers compared the breast cancer rates amoung 78,595 women who did not have a coil fitted with a similar number who had received a coil impregnated with progesterone officially called a levonorgestrel intrauterine device releasing systems (LNG-IUS). There are several types of LNG-IUD but the brand more commonly used in the UK is called the Mirena ® coil which contains the highest levels of progesterone (levonorgestrel-52mg).

The scientists found that women who opted for a progesterone coil had a 14% higher rate of breast cancer compared to women who had not and this was statistically significant. What’s more, the longer the coil was in place the higher the risk.

This data, unfortunately, does not make the decision for women considering hormone interventions any easier. We already know that oestrogen-only pills in women with a uterus increases the uterine cancer risk, which is why women with a uterus are always offered a oestrogen/ progesterone combination. Women with a uterus considering combined oestrogen progesterone combinations also have to trade off a lower risk of uterine, no increased risk of ovarian cancer but a potentially higher risk of breast cancer.

On the other hand, women without a uterus taking a oestrogen-only pill have a lower risk of breast cancer than the combined pill but data published earlier this year suggests they have a higher risk of ovarian cancer.

Pills which vary the dose of progesterone across the month seem to be better in terms of breast cancer risk. This may explain why the intrauterine progesterone in the coil, although producing lower dose in the blood stream, still produce a higher breast cancer risk because it produces a constantly dose hormone across the month.

It must be noted that, the relationship does necessarily directly mean the progesterone caused the breast cancer. Although, likely, it could mean that women opting for the coil have other risk factors for breast cancer - although this was not found.

Nevertheless, despite this caveat, Dr Lina Steinrud Mørch, who lead the research from The Danish Cancer Institute, Copenhagen, concluded that: “Given the increase in levonorgestrel-LNG-IUS use among females, information about breast cancer risk should routinely accompany discussions about benefits and risks.”

Breast cancer, despite improvements in detection and treatment remains a major concern for women, so any factor which increases the risk should be taken seriously. In 2022, there were around 2.3 million women diagnosed with breast cancer and 666,000 deaths globally, making it the leading cause of cancer deaths among women.

Despite these risks, progesterone coils can improve the quality of life for many women, improve contraceptive options for couples, hence improve sexual relationships and avoid the risks of unwanted pregnancy. In my wife's case, reducing blood loss and shortening the length of the period would hopefully have a major impact on reducing anaemia, improve fatigue levels and discomfort.

Overall, when considering relative risks of any type of hormone therapy, it’s useful to consider other crucial lifestyle factors which can significantly reduce the risk of cancer, including:

• Taking daily physical activity and avoiding long periods of sedentary behaviour
• Quitting smoking 
• Eating less meat and particularly processed meat
• Eating more phytochemical rich herbs, fruit, nuts and veg 
• Drinking less alcohol
• Ensuring adequate vitamin D levels
• Ensuring adequate essential mineral intake
• Reducing processed sugar intake
• Looking after your gut health
• Keeping a normal weight
• Avoiding oestrogenic environmental carcinogens

Further information on how and why lifestyle and diet interacts with cancer can be found in the book How to Live.