Hormone therapy, also called endocrine therapy or hormone- blocking therapy, is used to treat hormone receptor positive cancers (ER+ and/or PR+). The aim of hormone therapy is to slow or stop the growth of hormone receptor positive cancer cells.
There are different ways to reduce the level of female hormones in the body. The choice will depend on your age, the type of breast cancer and − for women − whether you have reached menopause.
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Tamoxifen is known as an anti-oestrogen drug. It works by stopping cancer cells from responding to oestrogen. Treatment with tamoxifen is usually started after surgery, radiation therapy or chemotherapy. It is commonly taken as a daily tablet for 5–10 years. It can be given to women of any age, regardless of whether they have reached menopause, and to men.
Your doctor will probably recommend using contraception while taking tamoxifen, as the drug may be harmful to a developing baby. In women, tamoxifen can cause menopausal symptoms, although it does not cause menopause. In men, the side effects can include low sex drive (libido) and erection problems.
You may also be at an increased risk of blood clots – see your doctor immediately if you have any swelling, soreness or warmth in an arm or leg. If you are having further surgery or travelling long distances, you may need to stop taking tamoxifen beforehand to lower the risk of blood clots. You can start taking it again when surgery or travel is completed.
A rare side effect is a higher risk of uterine cancer in postmenopausal women, so see your doctor if you notice any unusual vaginal bleeding.
You will probably not experience all of these side effects. Side effects usually improve as treatment continues and after it has finished. Your doctor and breast care nurse can give you information about ways to manage the side effects of tamoxifen.
Aromatase inhibitors help prevent the growth of hormone sensitive cancer cells by reducing the amount of oestrogen the body produces. They are recommended only for postmenopausal women, who are already producing smaller amounts of oestrogen. Before starting treatment with an aromatase inhibitor, you will have a bone density scan to check your bone health. Examples of aromatase inhibitors include anastrozole, exemestane and letrozole. They are taken daily as a tablet, usually for 5–10 years.
Side effects of aromatase inhibitors may include joint and muscle pain, bone thinning and weakening (osteoporosis), vaginal dryness, low mood, hot flushes and weight gain. For women with arthritis, aromatase inhibitors may worsen joint stiffness and pain. Exercise or medicines from your doctor may help with this.
For women who have not reached menopause, there are treatments that can stop the ovaries from producing oestrogen, either temporarily or permanently. These are sometimes recommended as an additional treatment for women taking tamoxifen.
Temporary ovarian treatment
Also known as ovarian suppression, this treatment includes the drug goserelin (brand name Zoladex), which stops oestrogen production. The drug is given as an injection by a nurse or your GP once a month for 2–5 years to bring on a temporary menopause. Side effects are similar to those of permanent menopause.
Permanent ovarian treatment
Ovarian ablation is treatment that permanently stops the ovaries from producing oestrogen. It usually involves surgery to remove the ovaries (oophorectomy). Ovarian ablation will bring on permanent menopause. This means you will no longer be able to become pregnant. If you may want to become pregnant in the future, ask your doctor for a referral to a fertility specialist before treatment starts.
For more on this, see Fertility and Cancer.