BMS consensus statement

Introduction

This is an important and controversial topic. The risk of breast cancer diagnosis associated with hormone replacement therapy (HRT) is often assumed by health care professionals and the lay public alike to be very high, which may adversely influence decisions about its initiation and continuance. This is despite the fact that most women will not be diagnosed in their lifetime and any risk conferred by HRT is comparable or less than that of other postmenopausal lifestyle risk factors for breast cancer (e.g. obesity, alcohol). The impact of HRT on breast cancer diagnosis is often discussed in isolation of its benefits and there is no or little simultaneous reference to the other lifestyle risk factors for breast cancer, to provide context when counselling women about its use. This consensus statement provides an overview of the association between HRT and breast cancer outcomes in women at low and higher risk of breast cancer. It has been updated in light of a recent meta-analysis in 2019 by the Collaborative Group on Hormonal Factors in Breast Cancer (CGHFBC) and publication in 2020 of the long-term outcomes from the placebo-controlled, randomised Women’s Health Initiative study (WHI).

Key points

1. In women with a low underlying risk of breast cancer (i.e. most of the population), the benefits of HRT for up to 5 years’ use for symptom relief will exceed potential harm.

• Unopposed estrogen is associated with no, or little change, in risk but this may be influenced by age at initiation
• There is no evidence of a dosage effect with estrogen
• Vaginal estrogen is not associated with an increased risk
• Combined HRT can be associated with an increased risk, which appears duration dependent
• Whilst risk with continuous combined HRT may be greater that with sequential HRT, the difference in risk is small and may be offset by protection against endometrial cancer
• Avoidance of synthetic progestogens in combined preparations may minimise risk
• Risk is limited to lean women
• Risk associated with HRT (including past users) is less than other lifestyle risk factors for breast cancer
• In women with POI, years of HRT exposure should be counted from the age of 50
• Communicating risk in terms of absolute excess risk with framing, minimises misinterpretation.

2. In women at high risk, or breast cancer survivors:

• There is no additive effect of HRT exposure in women at elevated personal risk due to a family history or high-risk benign breast condition
• Vaginal estrogen can be used in women taking tamoxifen but generally not aromatase inhibitors
• If the use of HRT or vaginal estrogen is considered, this should only be for the management of estrogen deficiency symptoms after discussion with the woman’s breast specialist team.