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Endocrine Therapy for Breast Cancer

Endocrine therapy also called Hormonal therapy for hormone receptor-positive breast cancer is an adjuvant therapy. Adjuvant therapy is treatment given after surgery, chemotherapy, and/or radiation therapy to lower the chance of the cancer coming back.

Hormone 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 hormone sensitive, i.e. oestrogen receptor (ER) or progesterone receptor (PR) positive.

Hormonal therapies used to treat breast cancer are not the same as hormone replacement therapy (HRT) used to manage symptoms of menopause.

Role of hormonal therapy in breast cancer

  • Reduces the size of the tumour before surgery (as neoadjuvant treatment)
  • Prevents the recurrence of the cancer, after surgical resection
  • Delays or completely stops the growth of cancer cells

There are different hormone 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 hormonal 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.

Types of hormonal therapy for breast cancer

Anti-oestrogens

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 increased risks of blood clots, such as deep vein thrombosis (DVT) or pulmonary thrombosis (PE), stroke and uterine cancers.

Aromatase inhibitors

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:

  • Have not yet reached menopause
  • Are in the middle of menopause
  • Have temporarily stopped having menstrual periods because of chemotherapy

Aromatase inhibitors are taken as a single tablet every day, usually for 5 years. But in conjunction with Tamoxifen 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

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.

Everyone is different in how they respond to treatment. If you experience significant side effects with your hormonal therapy, feel free to talk to your GP or oncologists, you may be able to take a different dose or different brand or different medicine.

Do not let side effects stop you from getting the benefits of hormonal therapy.