Letrozole (Femara)

Letrozole is also called Femara. It is a type of hormone therapy drug called an aromatase inhibitor, and is used to treat breast cancer.

Many breast cancers are stimulated to grow by the female sex hormones oestrogen and progesterone. These breast cancers are called hormone sensitive or hormone receptor positive and can be treated with drugs that block the effects of these hormones.

Women who have had their menopause don’t produce oestrogen from their ovaries. But they still produce a small amount by turning other sex hormones called androgens into oestrogen. Androgens are made by your adrenal glands, the small glands above your kidneys. Androgens need an enzyme called aromatase to turn them into oestrogen. This change happens mainly in fatty tissue, muscle and the skin. Aromatase inhibitors stop (inhibit) aromatase, so it can’t change the androgen into oestrogen. These drugs are only suitable for women who've had their menopause.

You take letrozole as a tablet, once a day.

It is very important that you take tablets according to the instructions your doctor or pharmacist gave you. Whether you have a full or empty stomach, for example, can affect how much of a drug gets into your bloodstream. You should take the right dose, not more or less. And never stop taking a cancer drug without talking to your specialist first.

There is general information about hormone therapies in the cancer treatment section.

We've listed the side effects associated with letrozole below. You can use the links to find out more about each side effect. Where there is no link, please go to the cancer drug side effects section or click on search at the top of the page.

More than 10 in every 100 women have one or more of these.

• Hot flushes and sweats – this happens in about 3 out of 10 women treated (30%)
• Painful joints – this affects about 1 out of 5 women treated (20%)
• Tiredness or fatigue – about 1 in 5 women treated (20%) get this side effect

Between 1 and 10 in every 100 people have one or more of these.

• Skin rashes – these are usually mild. You should let your doctor know if you have a rash. This happens in about 1 in 10 (10%) women having this treatment
• Headaches – in about 1 in 10 women (10%)
• Dizziness occurs in around 1 in 10 women (10%)
• Feeling or being sick – this is usually mild and can be easily controlled by anti sickness tablets, or if necessary injections. It affects about 1 in 10 women (10%)
• Fluid retention causing ankle and or finger swelling – this affects about 1 in 10 women (10%)
• Loss of appetite or indigestion
• Hair thinning
• Diarrhoea – if this happens it is usually mild. You should drink plenty of fluids. If it gets severe or persistent you could become dehydrated, so you should tell your doctor or nurse
• Constipation occurs in some people
• Vaginal dryness
• Lower interest in sex (reduced libido)
• Sadness or depression
• A cough and breathlessness – this affects less than 1 in 10 (10%) of women 
• Increased levels of cholesterol in the blood – this is usually only slightly increased. You will have regular blood tests to check the levels
• Loss of bone density – this is caused by a lack of oestrogen over a long period of time. When your bones are less dense they may break more easily. You should have a DEXA scan to check your bone density before you start treatment
• Vaginal bleeding – this mainly happens when women have changed from one type of hormone therapy to another during the first few weeks of treatment. You should tell your doctor or nurse if the bleeding continues. This affects fewer than 1 in 20 (5%) women treated

The side effects above may be mild or more severe. A side effect may get better or worse through your course of treatment, or more side effects may develop as the course goes on. This depends on

• How many times you've had the drug before
• Your general health
• The amount of the drug you have (the dose)
• Other drugs you are having

Talk to your doctor, pharmacist or nurse about all your side effects so that they can help you manage them. You should have a contact number for your chemotherapy nurse, clinic or ward nurse. You can ring if you have any questions or problems. They can give you advice or reassure you. If in doubt, call them.

Tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and other over the counter remedies – some drugs can react together.