Hormone-blocking therapy and metastatic breast cancer

Some breast cancers need female hormones (oestrogen and/or progesterone) to grow and reproduce. Hormones – particularly oestrogen – can encourage the growth of breast cancer that tests positive for hormone receptors. This type of breast cancer is called hormone receptor-positive breast cancer. 

In most cases treatment for hormone-receptor-positive metastatic breast cancer will start with hormone-blocking therapy given in the form of oral tablets. This treatment aims to deprive the breast cancer cells of the hormones they need to grow. 

How it works 

Hormone-blocking therapy is designed to either lower the level of oestrogen in your body or stop the oestrogen from stimulating the cancer cells. Your doctor may recommend this treatment if your tumour is hormone receptor-positive. 

How it's given 

Once started, each treatment is continued until it is no longer effective or side effects are sufficiently troublesome to prevent its use. Often a sequence of these treatments may control the cancer for a number of years. 

There are also now several targeted therapies that can be added to extend the length of control by hormone-blocking therapies and improve outcomes. Treatment will usually start with hormone-blocking therapy (oral tablets) with or without one of the targeted therapies called CDK 4/6 inhibitors. 

Occasionally, if there is concern that your cancer may cause serious problems for you in the near future, you may be advised that a course of chemotherapy should be given first to gain control of the cancer quickly. One example of this is if you have numerous symptoms from your cancer, liver metastases, or calcium levels above normal. Once chemotherapy is completed, people are usually able to proceed with hormone-blocking therapies.

Available therapies 

Some of the hormone-blocking therapies available currently include: 

• Anti-oestrogens – tamoxifen, fulvestrant (Fulvestrant Sandoz, Faslodex), toremifene (Fareston citrate)  
• Aromatase Inhibitors – anastrozole (Arimidex, Anastrozole FBM), letrozole (Femara, Letrozole FBM), exemestane (Aromasin)  
• Progestins – medroxyprogesterone acetate (Provera), megestrol (Megace)
• Ovarian suppression or ablation – goserelin (Zoladex). 

Considerations 

Which hormone-blocking therapy is right for me?

The hormone-blocking treatment recommended for you will depend on a number of factors, including: 

• what breast cancer hormone-blocking therapies you have taken previously – for instance, following a prior early breast cancer diagnosis 
• whether you were still taking a breast cancer hormone-blocking therapy when metastatic breast cancer was diagnosed 
• whether you are premenopausal (i.e. still having periods) or have had a hysterectomy and blood tests show your ovaries are still producing oestrogen 
• whether you are postmenopausal (i.e. your periods have stopped) and your ovaries are no longer producing oestrogen. 

If you have had a hysterectomy, you may need a blood test to determine whether you are premenopausal or postmenopausal.

If your breast cancer was metastatic when you were first diagnosed (e.g. de novo metastatic breast cancer), the main factor influencing the choice of hormone-blocking therapy is whether you are premenopausal or postmenopausal. If you have been using hormone replacement therapy or a hormonal contraceptive, then this will need to be permanently stopped. 

Side effects 

People taking hormone-blocking therapy for metastatic breast cancer may experience a range of side effects, including:

• Some aromatase inhibitors (AIs, e.g. Arimidex) can cause joint pain and stiffness. 
• The aromatase inhibitors can also lead to bone loss. If you are being treated with an AI you may be referred for bone mineral density tests to monitor your bone mineral density levels, particularly if you are at risk of developing osteoporosis. Bone mineral density tests are usually done using DEXA (dual X-ray absorptiometry) imaging test. A bone mineral density test is different from the bone scan that you may have to check whether your cancer has spread to other parts of your body. You may also have your vitamin D levels checked. For more information about bone health and vitamin D, read our bone health page. 
• Anti-oestrogen therapies and AIs may cause hot flushes, vaginal dryness and reduced libido. 
• Progestins may cause nausea and can also increase appetite, which can lead to weight gain. 
• Other side effects of hormone-blocking therapy may include fatigue, poor sleep, memory changes (poor short-term memory) and mood changes (anxiety and depression). 

You may experience some or none of these side effects. Talk to your treating team about any side effects you experience as there are often ways to manage them.  

Occasionally, you may need to stop a treatment because of side effects. In this case, there is usually another hormone-blocking therapy you can try. 

Note: Hormone-blocking therapy is sometimes confused with “hormone replacement therapy” (HRT), but they are completely different treatments.