Endocrine therapy is another form of systemic therapy. It is designed to either lower the level of oestrogen in your body or to stop the oestrogen from stimulating the cancer cells. Your doctor will recommend this treatment if your tumour is endocrine sensitive, i.e. oestrogen receptor (ER) or progesterone receptor (PR) positive.
Endocrine therapies used to treat breast cancer are not the same as endocrine replacement therapy (ERT) used to manage symptoms of menopause.
Role of endocrine therapy in breast cancer
There are different endocrine therapies for women who are pre-menopausal and those who are post-menopausal due to the different levels of oestrogen produced throughout these stages.
All endocrine therapies can cause menopausal symptoms. These include hot flushes, vaginal dryness, reduced libido (sex drive) and mood changes. The severity of these symptoms varies between women and between different treatments. These side effects often improve after treatment stops.
Anti-oestrogens work by stopping oestrogen in the body from attaching to cancer cells. One of the most well known anti-oetrogens is tamoxifen. Tamoxifen can be used to treat women of any age, regardless of whether they have reached menopause. Tamoxifen is taken as a single tablet every day, usually for 5 years. But, it can be up to 10 years.
Additional rare side effects include increase risks of blood clots, such as deep vein thrombosis (DVT) or pulmonary thrombosis (PE), stroke and uterine cancers.
Aromatase inhibitors (AIs) work by blocking oestrogen production, but only work for post-menopausal women. Examples of aromatase inhibitors include anastrozole (Arimidex®), letrozole (Femara®) and exemestane (Aromasin®).
Aromatase inhibitors are not suitable for women who:
Aromatase inhibitors are taken as a single tablet every day, usually for 5 years. But, it can be up to 10 years. If you are being treated with an AI, you may be referred to check your vitamin D level and for bone mineral density (BMD) tests to monitor your bone mineral density levels, particularly if you are at risk of developing osteoporosis.
Side effects of aromatase inhibitors include stiffness and pain in bones or joints (arthralgia) and increase risk of osteoporosis, which may increase the risk of bone fractures.
Ovarian suppressions work by stopping the ovaries from making oestrogen. Drugs like goserelin (Zoladex®), given as monthly injection, stop the ovaries from making oestrogen temporarily. They only work while the woman is taking the drug.
Drugs that stop the ovaries from working also cause menopause, but this usually only lasts while taking the drugs. However, the effects of these drugs may be permanent if a woman is close to her natural menopause when she starts treatment.
Oestrogen production can be stopped permanently by removing the ovaries surgically (oophorectomy) or giving radiotherapy to the ovaries. Ovarian treatments are only suitable for women who have not yet reached menopause.
Surgery to remove the ovaries or radiotherapy to the ovaries causes permanent menopause. Women who have these treatments can no longer have children naturally.