Study details
In the study, researchers evaluated all types of HRT commonly prescribed in the United Kingdom over the past 20 years, including topical estrogen, vaginal pessaries, and creams. They grouped HRT use by recent (within the past 5 years) and past (5 or more years ago) and HRT duration as short term (less than 5 years) and long term (5 years or longer). Results were adjusted for a range of factors that could affect breast cancer risk, including lifestyle, smoking, alcohol consumption, other medical conditions, family history, and use of other prescribed drugs.
The analysis included 98,611 women aged 50-79 years who were first diagnosed with breast cancer between 1998 and 2019. These women were matched by age and general practice to 457,498 women who were not diagnosed with breast cancer over these years. HRT use was reported in 34% (33,703) of women with breast cancer and in 31% (134,391) of women without breast cancer.
Overall, the risk for breast cancer was increased with use of most HRT drugs (adjusted odds ratio, 1.21; 95% confidence, 1.19-1.23), compared with not using HRT drugs. The highest risk was tied to combined estrogen/progestogen HRT (adjusted OR, 1.26; 95% CI, 1.24-1.29). The lowest risk was tied to estrogen-only HRT (adjusted OR, 1.06; 95% CI, 1.03-1.10). Estrogen cream and vaginal estrogen were not associated with increased breast cancer risk.
In general, breast cancer risk was higher among recent HRT users and those receiving long-term therapy. HRT-associated breast cancer risk increased with age and declined after discontinuing treatment. Therapy of less than 1 year was not associated with increased breast cancer risk.
Women who had recently been receiving long-term combined estrogen/progestogen HRT had a 79% increased risk for breast cancer (adjusted OR, 1.79; 95% CI, 1.73-1.85), compared with never-users. Among recent long-term users of combined HRT, breast cancer risk was highest for norethisterone (adjusted OR, 1.88; 95% CI, 1.79-1.99) and lowest for dydrogesterone (adjusted OR, 1.24; 95% CI, 1.03-1.48). Women who had recently been receiving long-term estrogen-only HRT had a 15% increased risk for breast cancer compared to never-users (adjusted OR, 1.15; 95% CI, 1.09-1.21).
Among women who discontinued HRT 5 or more years ago, risk for breast cancer was no longer increased for long-term estrogen-only therapy and short-term estrogen/progestogen therapy. However, breast cancer risk remained elevated 5 years after discontinuing long-term estrogen/progestogen (adjusted OR, 1.16; 95% CI, 1.11-1.21).
HRT-associated risk for breast cancer increased with age across all durations of therapy.
Compared with never-use, recent long-term estrogen-only therapy was associated with zero extra breast cancer cases per 10,000 women-years among women aged 50-59 years and eight extra cases per 10,000 women-years among women aged 70-79.
Recent long-term estrogen/progestogen use was associated with 15 extra breast cancer cases among women aged 50-59 and 36 extra cases among women aged 70-79 per 10,000 women-years.
Past long-term estrogen/progestogen use was associated with zero extra breast cancer cases among women aged 50-59 and eight extra cases among women aged 70-79 per 10,000 women-years.
Summarizing, Dr. Vinogradova said the increased risk for breast cancer with HRT appears to be “relatively small, particularly for younger women and for any women who use HRT only for a restricted period.”
Decisions about whether to use HRT and which type to use should depend on symptom severity, patient factors, and suitability of other treatment options, she commented.
“Particularly for those women who our study has shown to be most at risk, these decisions should be made through discussions between the patient and her doctor,” she concluded. “We hope that the new and more detailed information provided by our study will facilitate such prescribing decisions.”
The study was partially funded by the School for Primary Care Research of the National Institute for Health Research, by Cancer Research UK, and by the Cancer Research UK Oxford Center. Dr. Vinogradova has disclosed no relevant financial relationships. Senior author Julia Hippisley-Cox is an unpaid director of QResearch and was a paid director of ClinRisk until 2019. The other authors have disclosed no relevant financial relationships.
A version of this story originally appeared on Medscape.com.