This information is about a hormonal therapy called letrozole, which is also commonly called Femara®. It is used to treat breast cancer. The information should ideally be read with our information about breast cancer and about secondary breast cancer.

Femara is a type of hormonal therapy that is used in the treatment of breast cancer in women who have had their menopause (change of life).

Hormonal therapies interfere with the production or action of particular hormones in the body. Hormones are substances produced naturally in the body. They act as chemical messengers and help to control the activity of cells and organs.

There are several different types of hormonal therapy. Your doctor can discuss with you which is best for your particular situation.

Many breast cancers rely on supplies of the hormone oestrogen to grow. In women who have had their menopause, the main source of oestrogen is through changing androgens (sex hormones produced by the adrenal glands) into oestrogen. This is carried out by an enzyme called aromatase. The conversion process is known as aromatisation, and happens mainly in the fatty tissues of the body.

Femara is a drug that blocks the process of aromatisation, and so reduces the amount of oestrogen in the body. Drugs that work in this way are known as aromatase inhibitors. Other aromatase inhibitors include anastrozole (Arimidex®) and exemestane (Aromasin®).

Femara is a tablet which is taken once a day, ideally at about the same time each day. It does not matter whether this is in the morning or the evening.

Doctors take into account many different factors when planning each person's treatment, so it is important to talk things over with your specialist. They will make a decision about treatment based on current medical knowledge and your individual situation.

Early breast cancer

Femara can be used to treat women with early breast cancer (cancer that hasn't spread) after they have had surgery to remove the cancer. Giving treatment after surgery is known as adjuvant therapy. Hormonal therapy is usually given for five years.

Femara can also be given to women after they have had a few years treatment with another hormonal drug called tamoxifen.

Sometimes Femara may be given before surgery to women with localised early breast cancer, to allow them to have a lumpectomy (removal of the lump) rather than a mastectomy (removal of the breast). Giving treatment before surgery is known as neo-adjuvant therapy.

Advanced breast cancer

Femara may be used to treat women whose breast cancer has spread to other parts of the body (advanced or metastatic breast cancer). It may also be used to treat women whose cancer has come back after treatment with other hormonal therapies.

Each person's reaction to any medication is different. Most people have very few side effects with Femara, while others may experience more. The side effects described in this information will not affect everyone and may be different if you are having more than one drug.

We have outlined the most common side effects. However, we have not included those which are very rare and extremely unlikely to affect you.

If you notice any effects that you think may be due to the drug, but which are not listed in this information, please discuss them with your doctor or nurse.

You will see your doctor regularly while you have this treatment so that they can monitor you.

Some people may have the following side effects to varying degrees:

Feeling sick (nausea), and being sick (vomiting) These effects are rare and usually mild. Feelings of sickness can often be relieved by taking your tablet with food or milk, or at night. Let your doctor know if any of these effects are troublesome, as medicines can usually be prescribed to control them.

Tiredness and headaches These are not common. It is important to get enough rest. Let your doctor know if you are getting headaches, as medicines can be prescribed to help.

Muscular aches and joint pain These are rare, but if they occur let your doctor know, as medication may be prescribed.

Hot flushes These are usually mild and may wear off after a period of time. Some people find that it is helpful to cut down on tea, coffee, nicotine and alcohol. Recent research suggests that progestogen or some types of antidepressants may be helpful in controlling this side effect. Your nurse or doctor can discuss this with you.

Some women have found complementary therapies helpful. Your GP may be able to give you details about obtaining these on the NHS.

Hair thinning Some women notice that their hair thins while taking Femara, but this is usually mild.

Vaginal dryness This may occur while using Femara. Gels that can help to overcome the dryness are available. The gels can be bought from any chemist or can be prescribed by your doctor.

Risk of osteoporosis Women who have osteoporosis (weakened bones) or are at risk of it, should have their bones assessed before and during treatment with Femara. In some situations it may be necessary to start treatment to help prevent osteoporosis.

Your doctors will discuss the length of treatment that they feel is appropriate for your situation. Femara is often given over a period of years, or for as long as it is controlling your cancer, depending on your individual situation.

Femara may interact with other medicines. Let your doctor know about any medications you are taking, including non-prescribed drugs such as complementary therapies and herbal drugs.

• Keep the tablets in a safe place where children cannot reach them, as Femara could harm them.
• If your doctor decides to stop the treatment, return any remaining tablets to the pharmacist. Do not flush them down the toilet or throw them away.
• If you forget to take your tablet, do not take a double dose. Let your doctor or nurse know. Don't worry, the levels of the drug in your blood will not change very much, but try not to miss more than one or two tablets in a row.
• Remember to get a new prescription a few weeks before you run out of tablets. Make sure that you have plenty for holidays.

This section has been compiled using information from a number of reliable sources including:

• Martindale: The Complete Drug Reference (35th edition). Sweetman et al. Pharmaceutical Press, 2007.

• British National Formulary (56th edition). British Medical Association and Royal Pharmaceutical Society of Great Britain, September 2008.

For further references, please see the general bibliography.