Studies have shown that unopposed oestrogen increases the risk of both endometrial hyperplasia and of endometrial endometrial carcinoma - by a factor of eight. The effects are usually apparent 2 years after treatment.).
However, it has been shown that the inclusion of 7-10 days of progestagen in the 28 day cycle reduces the increased risk; however the addition of progestogen does not eliminate the risk of endometrial cancer associated with HRT use (1).Observational studies suggest that there are about 20 extra cases of endometrial cancer per 1000 women treated with oestrogen-progestogen combination, compared with the estimate of 42 extra cases of endometrial cancer with oestrogen-only therapy (1).
The MHRA has summarised the risks of HRT with respect to breast, endometrial and ovarian cancer (2):
Summary of HRT risks and benefits* during current use and current use plus post-treatment from age of menopause up to age 69 years, per 1000 women with 5 years or 10 years use of HRT (2)
Reference:
- Current Problems in Pharmacovigilance (2002), 28, 1-3.
- MHRA (August 2019). Hormone replacement therapy and risk of breast cancer
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