Hormone-blocking therapy

Hormone-blocking therapies are drugs used to treat hormone receptor-positive breast cancer. 

Around two-thirds of breast cancers are hormone receptor-positive, which means that they need female hormones (oestrogen and/or progesterone) to grow and reproduce. Most people with hormone receptor-positive breast cancer will be offered hormone-blocking therapy (sometimes called endocrine therapy). 

Tamoxifen is one of the best-known hormone-blocking therapy medications. It can be used to treat pre and post-menopausal people. Aromatase inhibitors such as anastrozole, letrozole and exemestane are also hormone-blocking therapies, however they are only suitable for people who have completed menopause (post-menopausal). 

Note: Hormone-blocking therapy used to treat breast cancer is not the same as hormone replacement therapy (HRT) used to manage the symptoms of menopause. 

How it works 

Hormone-blocking therapy works by depriving breast cancer cells of the hormones such as oestrogen that they use to grow. Different hormone-blocking medicines do this in different ways.

Hormone-blocking therapy is designed to either lower the level of oestrogen in your body or block the effects of oestrogen on breast cancer cells. 

Hormone-blocking therapy is usually given after early breast cancer treatments such as surgery, radiotherapy or chemotherapy (called adjuvant therapy). It has been found to be very effective in reducing the risk of the breast cancer coming back (recurrence), or of a new breast cancer developing in the same or other breast. Hormone-blocking therapy may also be used to shrink a tumour before surgery (neoadjuvant therapy).

For people with hormone receptor-positive metastatic breast cancer, hormone-blocking therapy is used to help shrink or slow the growth of their cancer. It is usually taken for as long as it works. When a particular hormone-blocking therapy stops being effective, your treating doctor may usually recommend a different one. 

How it is given

Hormone-blocking therapy is given as an oral medication. For people with early breast cancer, it is usually recommended that it is taken daily for at least five years after the completion of your other breast cancer treatments (surgery, chemotherapy and/or radiotherapy). Research shows that taking hormone-blocking therapy for up to 10 years may further reduce the risk of breast cancer returning. Some people are now recommended 10 years of hormone-blocking treatment.  

For people who are pre-menopausal, ovarian suppression treatment may be given in combination with oral hormone-blocking therapy. This may be necessary as oestrogen is mainly produced in the ovaries prior to menopause. Ovarian suppression can be in the form of monthly injections or surgery. 

Side effects 

Hormone-blocking therapy can have side effects, including: 

• Menopausal symptoms such as hot flushes, night sweats, heart palpitations, weight gain, mood swings and reduced libido 
• Anxiety 
• Sleep disturbance 
• Fatigue. 

Aromatase inhibitors can cause joint stiffness and pain as well as thinning and weakening of the bones. This can result in bone fractures and osteoporosis. Your doctor may recommend that you have a bone mineral density scan, called a DXA or DEXA scan, before starting your treatment. You may also have your calcium and Vitamin D levels checked. Sometimes you may be prescribed a bone strengthening medication to protect your bones from fractures.  More information is available on the bone health page . 

If you are finding side effects of hormone-blocking therapy difficult to manage, talk to your medical oncologist. They may be able to give you some advice to help you manage side effects, or switch you to one of the other hormone-blocking therapy drugs.