Aromatase inhibitors

Aromatase inhibitors (AIs) are a type of hormonal therapy that reduce the levels of oestrogen in the body. They work by blocking the production of oestrogen in body tissues. For many postmenopausal women it is helpful to have an aromatase inhibitor as part of hormonal therapy treatment| . AIs may be given on their own or in combination with the drug tamoxifen| .

There are three AIs currently in use:

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

Many women can take aromatase inhibitors without any problems, but some may experience mild to moderate side effects, including hot flushes, feelings of sickness, joint pains and vaginal dryness.

How do they work?

To understand how AIs work, it helps to know a little about the way oestrogen is made.

In women who have not had their menopause (premenopausal women), the main source of oestrogen is the ovaries. In women who have had their menopause (postmenopausal women) oestrogen is made by a process known as aromatisation. This is an activity in which sex hormones (androgens) produced by the adrenal glands are turned into oestrogen in the fatty tissue of the body. A chemical in the body called aromatase makes this happen.

Aromatase inhibitors block the process of aromatisation, and so reduce the amount of oestrogen in the body. This means that the hormone receptors are exposed to less oestrogen and the cancer cells receive fewer signals to grow. AIs are currently only suitable for post-menopausal women, although research is being carried out into using them in pre-menopausal women who have been put into a temporary menopause by using medicines such as Zoladex®. Your doctor can give you more information on this or you can talk to our nurses| .

When are they given?

Aromatase inhibitors and early breast cancer

Several studies have looked at the effectiveness of AIs in primary (early) breast cancer when compared with tamoxifen. The results have been encouraging, and the three main aromatase inhibitors are now licensed to treat post-menopausal women with ER-positive early breast cancer.

Aromatase inhibitors and advanced breast cancer

Aromatase inhibitors have been used to treat women with advanced (secondary or metastatic| ) breast cancer since the mid-1990s, and their use in this situation is well established. This information is about AIs for early breast cancer, but if you would like information about their use in advanced breast cancer you can contact our nurses| .  

How are they taken?

Arimidex, Aromasin and Femara are all taken as tablets once a day. They should ideally be taken at around the same time every day.

Deciding which hormonal therapy to use

Your doctor will discuss the different types of hormonal therapy with you and will outline the possible side effects. Together you can decide which one is right for you. NICE (National Institute for Clinical Excellence) published its recommendations for the treatment of early and localised breast cancer in February 2009. This includes information on aromatase inhibitors.

NICE recommends anastrozole or letrozole as the first line hormonal therapy for postmenopausal women with early breast cancer if their cancer has a more than low-risk of coming back. Aromatase inhibitors can also be used in people who aren’t able to take tamoxifen, or for whom tamoxifen causes severe side effects.

NICE recommends that women who have already had 2–3 years treatment with tamoxifen can be offered exemestane or anastrozole.

For women who had cancer in their lymph nodes when they first had surgery, and who have already had 5 years of tamoxifen, NICE recommends offering treatment with letrozole for another 2–3 years.