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Title More evidence on HRT and breast cancer
Date 30 July 2020
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The first publication of the Women's Health Initiative trial in 2002, raised alarm about risks of HRT, with an increase in breast cancer in women who took HRT particularly concerning. Despite the fact that many publications since have often shown reassuring findings, many women and healthcare professionals have continued to be concerned about using HRT because of this risk.

In 2019 data from observational studies again caused alarm by stating that the risk with all types of HRT, apart from vaginal estrogen, was greater than previously believed and that breast cancer mortality was increased in women who took HRT See the news item here

The latest publication reports on long term follow up from the Women's Health Initiative randomised trials and is likely to provide more reliable information than that from the previously reported observational studies. In total, 27,347 postmenopausal women aged 50 to 79 were enrolled into the studies from 1993 to 1998 and were followed up until end of December 2017.

For women who had had a hysterectomy, 10,739 were randomised to take estrogen only HRT or placebo. The women who took estrogen only had a statistically lower breast cancer incidence and lower breast cancer mortality than those who took placebo.

16,608 women who still had a uterus (had not had a hysterectomy), were randomised to HRT containing estrogen and progestogen (combined HRT) or placebo. Women who took combined HRT had a statistically increased breast cancer incidence but no increase in breast cancer mortality.

These findings are in keeping with the NICE guideline published in 2015. The small increased risk of breast cancer in women taking combined HRT is believed to be due to the combined HRT promoting the growth of breast cancer cells which are already present, rather than causing the breast cells to become cancerous.

Unless women have had a hysterectomy, combined HRT is recommended rather than estrogen only, since the addition of progestogen is required to prevent estrogen stimulating the uterine lining. The WHI trial used a particular type of estrogen (conjugated equine estrogen) and one specific progestogen (medroxyprogesterone acetate). It is possible that different types of estrogen and progestogen may not have the same effects.

The confirmation of no increased breast cancer mortality from either estrogen only or combined HRT, should provide reassurance both to women and healthcare professionals.

Every woman should be able to make an informed choice about whether or not to take HRT, and for how long. Information about breast cancer risk should be balanced individually against benefits which include symptom control, reduced cardiovascular risk when HRT is started within ten years of the menopause and improved bone health with reduced risk of osteoporosis and osteoporotic fracture.

See joint statement from Royal College of Obstetricians and Gynaecologists and British Menopause Society

Reference: Association of Menopausal Hormone Therapy With Breast Cancer Incidence and Mortality During Long-term Follow-up of the Women's Health Initiative Randomized Clinical Trials

Rowan T.Chlebowski, MD,PhD1; Garnet L. Anderson, PhD2; Aaron K. Aragaki, MS2
JAMA. 2020;324(4):369-380. doi:10.1001/jama.2020.9482

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