Hormone-blocking therapy

Hormone-blocking or hormone-reducing therapy is offered to most people with hormone receptor-positive (HR+) breast cancer.

It is also called ‘endocrine therapy’.

Treatment is different for each person. Your medical oncologist can explain why they are recommending particular treatments for you.

Read about Hormone-receptor positive breast cancers.

How hormone-blocking therapy works

Hormone-blocking and hormone-reducing drugs stop breast cancer cells from getting the hormones they need to grow. Different types of therapies do this in different ways. They may:

• block the effects of oestrogen on breast cancer cells. The drugs attach to the oestrogen receptors on breast cancer cells so oestrogen cannot enter the cells and help them grow
• lower the level of oestrogen the body produces in tissues (muscles, fat cells and the adrenal glands), so less oestrogen is circulating in the body.

For early breast cancer and DCIS

For people with early breast cancer or DCIS, hormone-blocking treatment aims to:

• reduce the risk of the breast cancer coming back (‘recurrence’)
• reduce the risk of a new breast cancer developing in the same or other breast.

Usually for early breast cancer you take a daily tablet for 5 to 10 years. For DCIS, some people are recommended endocrine therapy for 5 years.

For metastatic breast cancer

For people with metastatic breast cancer, the aim is to reduce the risk of the cancer getting worse by helping shrink or slow the growth of the cancer.

It may be a few months before your doctor can tell whether a particular therapy is working.

You will continue each treatment until:

• it is no longer effective, or
• side effects become too hard to tolerate.

If it stops working after a time, there are usually other therapies or treatments to try.

These treatments can sometimes control the cancer for a number of years.

Read about Hormone-blocking therapy for metastatic breast cancer.

How it is given

Endocrine therapy can be a tablet or an injection.

For people with early breast cancer, the recommendation is usually a daily tablet for at least 5 years. This starts after you finish other treatments (surgery, chemotherapy and/or radiotherapy).

Research shows that taking hormone-blocking therapy for up to 10 years may further lower the risk of breast cancer returning. Some people are now recommended 10 years of hormone-blocking treatment.

Doctors sometimes recommend hormone-blocking therapy before surgery (called neoadjuvant treatment). This may be to reduce the tumour first, or if surgery has to be delayed.

Types of hormone-blocking therapy

There are different types of hormone-blocking therapy drugs.

The main types are:

• Anti-oestrogens
• Aromatase inhibitors
• Ovarian suppression or removal.

Your medical oncologist or surgeon will consider several factors before they recommend a drug. These factors include:

• the type and subtype of cancer
• whether you are pre or post-menopausal.

Anti-oestrogens

Drugs that target oestrogen receptors are commonly used to treat HR+ breast cancer. Anti-oestrogens can be used to treat women of any age, regardless of whether they’ve reached menopause.

It may also be used in women after menopause if aromatase inhibitors are not suitable (for example, if they have poor bone density).

Tamoxifen (Nolvadex) is a common hormonal therapy for early breast cancer. It was the first hormone-blocking treatment used in breast cancer in the 1970s.

Aromatase inhibitors

Aromatase inhibitor drugs reduce the amount of oestrogen in the body by blocking the enzyme 'aromatase'. This aims to slow or stop the cancer from growing. 

These therapies include:

• anastrozole (Arimidex)
• letrozole (Femara)
• exemestane (Aromasin).

Aromatase inhibitors are only effective for women who:

• have gone through menopause
• are premenopausal and using a medication such as goserelin (Zoladex) to stop ovarian function.

They are commonly used after surgery to lower the risk of recurrence.

Ovarian suppression or removal

Treatments targeting the ovaries are only prescribed to women who are premenopausal. These treatments stop the ovaries from making oestrogen, which ‘feeds’ hormone receptor positive breast cancer.

The purpose of this treatment is to put you into an early menopause. This may be temporary or permanent.

You may have ovarian suppression treatment and a hormone-blocking tablet.

• Goserelin (Zoladex) is a common temporary treatment given by monthly injections under the skin.
• Another option for pre-menopausal women is surgery to remove ovaries (‘oophorectomy’). This is permanent.
• Rarely, radiation to the ovaries is used to shut down the ovaries permanently.

Side effects

You may have side effects from hormone-blocking drugs, such as:

• symptoms of menopause (hot flushes, night sweats, heart palpitations, weight gain)
• anxiety
• problems sleeping
• fatigue
• aches and pains in your joints.

The side effects are different for each type of hormone-blocking therapy. For most women, these symptoms ease over time.

Findings of past clinical trials

Clinical trials have been important in showing us the benefits of hormone-blocking therapies. Previous research has found:

• Women who took a hormone-blocking therapy for 5 years were less likely to have a breast cancer recurrence than women who did not. Even after 5 years, women who were no longer taking hormone-blocking therapies were still much less likely to have a recurrence. The benefits of hormone-blocking therapies are ongoing and last well beyond the 5 years you take them.
• For some women, taking tamoxifen or an aromatase inhibitor for 10 years provides even further protection against breast cancer recurring. Your medical oncologist can discuss whether this could benefit you.