Breast cancer risk persists after HRT discontinuation
A recent meta-analysis of worldwide epidemiological evidence has indicated that the increased risk of breast cancer associated with hormone replacement therapy (HRT; now often referred to as menopausal hormone therapy) is higher than previous estimates have suggested (Lancet 2019;394(102040):1159–68).
The analysis, carried out by the Collaborative Group on Hormonal Factors in Breast Cancer, used data collected between 1992 and 2018 from worldwide prospective studies (both published and unpublished) that included information on the type and timing of HRT use in women who developed breast cancer.
Of the 108,647 postmenopausal women who developed breast cancer during prospective follow-up, 51% had used HRT. Among women for whom complete information was available, mean duration of HRT use was 10 years in current users and seven years in past users; the average age when starting therapy was 50 years. All types of HRT, with the exception of vaginal oestrogen, were associated with excess breast cancer risk, which increased with duration of use and was greater for combined oestrogen/progestogen preparations than oestrogen-only preparations. Moreover, after ceasing HRT, some excess risk persisted for over 10 years, with the magnitude of risk dependent on the duration of previous use, although there was little excess risk with under one year of use.
Applying these data, the study authors estimate that five years of HRT use starting at aged 50 years, in women of average weight, would increase the 20-year breast cancer incidence by about one in every 50 users of oestrogen/daily progestogen HRT, one in 70 users of oestrogen/intermittent progestogen HRT and one in 200 users of oestrogen-only preparations, assuming the associations are causal.
In response to this study, the MHRA has issued advice to prescribers to discuss the risks and benefits of HRT to current and past users, and to those contemplating use, at their next routine appointment. Women should be advised to be vigilant for signs of breast cancer, even after stopping HRT, and be encouraged to attend for breast screening when invited. The MHRA advises that HRT should only be prescribed for the relief of postmenopausal symptoms that have an adverse effect on quality of life, women should use the lowest effective dose for the shortest duration, and therapy should only be continued for as long as the benefit in alleviating symptoms outweighs the risks associated with treatment.