The Use of Hormone Replacement Therapy and Risk of Breast Cancer: What You Need to Know

The risk of breast cancer associated with hormone replacement therapy (HRT) has been a topic of concern and discussion for both healthcare professionals and women. However, it is important to note that the perceived risk of breast cancer with HRT is often exaggerated and may influence decisions about its use. While HRT does carry some risk (3% increase), it is comparable to other lifestyle factors such as lack of exercise (3% increase), obesity (9% increase) and alcohol consumption (6% increase).

One reason for the negative attention surrounding HRT is the way it has been portrayed in the media. Reports often emphasise the risks of HRT, while studies that show no adverse effects receive little attention. This unbalanced reporting can lead to a misinterpretation of the actual risks involved. It is crucial to provide a more comprehensive perspective by discussing the benefits of HRT alongside its potential risks and considering the context of other lifestyle risk factors for breast cancer.

Numerous observational studies have been conducted to evaluate the association between HRT and breast cancer outcomes. The findings from the Collaborative Group on Hormonal Factors in Breast Cancer, the Women's Health Initiative Study, and the Million Women's Study have heavily influenced clinical advice and prescribing habits. These studies identified a duration-dependent association between HRT and the risk of breast cancer diagnosis, with the risk increasing after five years of exposure. However, it is important to note that the overall risk conferred by HRT is relatively small, equivalent to the impact of delayed menopause.

The Women's Health Initiative Study and the Million Women's Study confirmed that the risk of breast cancer with HRT is greater with combined therapy compared to unopposed therapy. While the estimated risk is consistent with previous clinical studies, the results of these studies led to a significant decrease in HRT prescribing worldwide. Unfortunately, the emphasis on risk ratios and percentage change in risk in these studies led to misinterpretation and negative publicity. Presenting findings using absolute excess or attributable risk could have provided a clearer understanding of the actual risk.

With up to five years of use, exposure to any unopposed oestrogen is associated with minimal or no increased risk of breast cancer. The type or route of oestrogen administration does not seem to impact the risk significantly, except for implants where there is a lack of clinical data. Long-term use of combined HRT (oestrogen + progesterone) may potentially increase the risk, but further confirmation is needed.

The National Institute for Health and Care Excellence (NICE) has published menopause guidance that includes an evaluation of the short-term outcomes of HRT for the treatment of menopausal symptoms on breast cancer outcomes. The guidance recommends individualised counselling, accounting for non-modifiable factors that determine baseline breast cancer risk and exposure to modifiable lifestyle risk factors.

While modifying risk factors can have a positive impact on reducing breast cancer diagnosis for the population as a whole, it is important to recognise that it is not possible to predict at an individual level who will benefit or not. Most women exposed to known risk factors, including HRT, are never diagnosed with breast cancer during their lifetime. Therefore, discussions about HRT should take into account the overall risk-benefit ratio, especially for women at population risk for breast cancer, where the benefits of HRT in terms of all-cause mortality reduction outweigh the potential risks.

In summary, for women with a low underlying risk of breast cancer, the benefits of HRT in the short term for symptom relief outweigh the potential harm. The risk of breast cancer associated with HRT is equivalent to or less than that of other lifestyle risk factors, like lack of exercise, alcohol use and obesity). It is important not to discuss the potential risk of breast cancer with HRT in isolation but to consider its other short- and long-term benefits and risks. Individualised counselling, accounting for baseline breast cancer risk and exposure to modifiable lifestyle risk factors, is crucial for making informed decisions about HRT use.

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