Menopausal hormone therapy (MHT) also known as hormone replacement therapy (HRT)
Oral or transdermal (patch)
There is convincing evidence that use of oral or transdermal oestrogen-only menopausal hormone therapy (MHT)* is associated with an increased risk of endometrial cancer. The risk increases the longer a woman uses oral or transdermal oestrogen-only MHT. The increased risk continues for at least 10 years after stopping use.
Women who use oral or transdermal oestrogen-only MHT are twice as likely to develop endometrial cancer as women who never use MHT. For this reason, oestrogen-only MHT is usually only recommended for women who have had a hysterectomy.
It is estimated that about 3% of cases of endometrial cancer in Australia are due to women using oestrogen-only MHT.
Oestrogen is one of two important female hormones. It affects how endometrial cells grow and divide and can increase the risk of endometrial cancer. The effects of oestrogen on endometrial cells are balanced by the effects of the female hormone progestogen. When a woman uses oestrogen-only MHT, her levels of oestrogen are higher than her levels of progestogen. It is this increased level of ‘unopposed’ oestrogen that can increase the risk of endometrial cancer.
There is no conclusive evidence that vaginal oestrogen-only MHT affects the risk of endometrial cancer. Only a small number of studies have been conducted and the small amount of evidence suggests no association.
*Oestrogen-only MHT is a form of hormone replacement therapy that doesn’t include a progestogen. It may be given as a pill (oral), via a patch (transdermal) or in the form or a cream, ring or pessary placed in the vagina.
Combined oestrogen–progestogen MHT
Using continuous oestrogen-progestogen MHT* may be associated with a decreased risk of endometrial cancer. However studies have given inconsistent results.
Cyclical (progestogen at least 10 days/month)
There is no conclusive evidence that using cyclical oestrogen–progestogen MHT in which progestogen is given for 10 or more days per month is associated with an increased or decreased risk of endometrial cancer. Results from studies are not consistent and studies are of limited quality.
*Oestrogen-progestogen MHT is a form of hormone replacement therapy that uses a combination of oestrogen and progestogen. The two hormones may be used on each day of the month (continuous), or progestogen may be given for only some days of the month (cyclical). Progestogens are added to oestrogen for at least 10 days per month to reduce the increased risk of endometrial cancer associated with oestrogen-only MHT.
Use of tibolone is probably associated with an increased risk of endometrial cancer.
The risk of endometrial cancer is estimated to be between 2 and 4 times higher in women who use tibolone compared to women who do not use MHT. One study suggests that the risk may increase with longer use.
Once in the body, it acts like oestrogen, progestogen, and testosterone. Studies suggest that tibolone acts more like oestrogen than progestogen on the womb. This oestrogen-like effect may be what leads to the increased risk of endometrial cancer.
* Tibolone is a synthetic form of hormone replacement therapy.