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Hormone replacement therapy (HRT)

Doctors sometimes prescribe hormone replacement therapy (HRT) to relieve symptoms of menopause. Hormone replacement therapy may also be called hormone therapy (HT) or menopausal hormone therapy (MHT). Many studies have looked at HRT and the health risks linked to its use, including certain cancers. The evidence about the risks and benefits of HRT comes from large clinical trials, such as the Women’s Health Initiative (WHI) done in the USA and the British Million Women Study.


Menopause occurs naturally as women age. It is the transition from a womans childbearing years to her non-childbearing years. Menopause is caused by reduced levels of the hormones made by the ovary, mainly estrogenestrogenA female sex hormone that causes the female sex characteristics to develop (such as breasts) and is necessary for reproduction. and progesteroneprogesteroneA female sex hormone that prepares the uterus (womb) for pregnancy and the breasts for lactation following childbirth.. This change in hormone levels may cause:

  • hot flashes
  • sleep disturbances
  • mood swings

Menopause often happens when a woman is in her early 50s, but when it begins and ends can vary a lot among women. Menopausal symptoms typically continue for several years until menstrual periods stop completely. Women with cancer may enter menopause early as a side effect of chemotherapy or other cancer treatments.

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Types of HRT

The 2 main types of HRT that may be used to relieve menopausal symptoms are:

  • combined HRT –  contains a combination of estrogen plus progestin (a synthetic form of progesterone)
    • The combination of an estrogen and progestin (estrogen-progestin therapy or EPT) is often used because estrogen alone can increase the risk of uterine (endometrial) cancer, and progestin appears to decrease this risk.
  • estrogen only
    • Estrogen only (estrogen alone) therapy does not contain progestin and is mainly used for women who have had their uterus removed by surgery (hysterectomy). Women who have had a hysterectomy are not at risk for uterine cancer.

HRT comes in many doses and forms including a pill, nasal spray, injection into the fatty tissue under the skin (subcutaneous implant), vaginal ring, cream, skin patch or gel.

Bioidentical hormones

Some hormone products can be bought without a prescription and may be referred to as bioidentical hormones. Bioidentical hormones are made from plant sources and are basically the same as hormones made by our bodies. Supporters of the products say that they are safer or more natural, but there is no scientific evidence that bioidentical hormones are less risky or more effective than prescribed hormones.

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Combined HRT and cancer

Although combined HRT may protect against osteoporosis (loss of bone density), research shows that the risks of long-term use of combined HRT outweigh the health benefits for most women.

  • The International Agency for Research on Cancer (IARC) states that there is sufficient evidence that post-menopausalpost-menopausalThe time after menopause. women taking combined HRT have an increased risk for breast cancer.
    • Studies show that the increased risk for breast cancer begins within 5 years of starting combined HRT. The risk of breast cancer increases the longer combined HRT is used.
    • Combined HRT use is linked to increased breast density, which is a known risk factor for breast cancer.
    • The risk of breast cancer decreases after HRT is stopped. It is thought that the risk returns to that of a woman who has never used HRT (average risk) within a few years of stopping HRT.
    • It is not known whether the risk for breast cancer differs depending on the type, dose or how the HRT is given.
    • A 2010 Canadian study showed a considerable decrease in breast cancer incidence among post-menopausal women from 2002–2004. This decline in breast cancer corresponded with a drop in HRT use during this time period.
  • There is a very small increased risk for ovarian cancer in women who take combined HRT. The increased risk also occurs after 5 or more years of taking combined HRT, however the evidence has not been consistent across the studies.
  • It is unlikely that combined HRT increases the risk of colorectal cancer.

Studies have also shown there is an increased risk for other health problems such as heart attack, stroke and blood clots with combined HRT use.

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Estrogen-only therapy and cancer

There are also cancer risks associated with estrogen-only therapy (ET) for treating menopausal symptoms.

  • The International Agency for Research on Cancer (IARC) states that there is sufficient evidence that estrogen-only therapy causes cancer of the uterus and ovary.
    • The risk of uterine and ovarian cancer increases with the length of time that ET is used.
    • ET also increases the risk for atypical endometrial hyperplasia, a precancerous condition of the uterus.
    • The risk of uterine cancer lessens with time, but it may continue for more than 10 years after taking ET.
    • The risk of uterine cancer from estrogen-only therapy is reduced by adding progestin to the therapy and appears to depend on the number of days each month that progestin is taken. However, it’s unclear whether adding any amount of progestin reduces the risk completely.
  • Some studies have reported a small increase in breast cancer risk with ET use.
  • ET may decrease the risk of colorectal cancer.

Studies have also shown ET use increases the risk of other health problems, such as stroke and blood clots.

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HRT use after cancer

If you have a history of cancer and are thinking about taking HRT, you should know the risks associated with it.

  • Some women with a history of breast cancer may be advised not to take HRT because of a possible relationship between estrogen and recurrent breast cancer. This link is not fully understood and there have been conflicting results from studies that test the effects of HRT on women with breast cancer.
  • Although women at increased risk for breast cancer are usually advised not to take HRT, it may be an option for some women if they have proper counselling and follow-up.
  • Some women with a history of uterine cancer may be advised not to take HRT, especially women who have had higher stage and higher grade uterine tumours.

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Reducing your risk

Women should avoid combination HRT for any reason other than to relieve severe menopausal symptoms that have not responded to any other treatment. Talk to your doctor about your menopausal symptoms and HRT to determine the best course of action for you.

  • How severe your menopausal symptoms are and your medical history should be considered when deciding if you should take HRT.
  • If you and your doctor decide that HRT is right for you, it should be used for the shortest period of time and lowest dose possible to control your menopausal symptoms.
  • Report any abnormal vaginal bleeding to your doctor.

You may decide not to take HRT and try other ways to relieve your menopausal symptoms.

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