This information is about a hormonal therapy called toremifene that is used to treat breast cancer. It should ideally be read with our general information about breast cancer or secondary breast cancer.

Toremifene is a hormonal therapy used to treat women with breast cancer who have had their menopause (change of life). It is occasionally used to treat women whose cancer has spread to other areas of the body (advanced breast cancer).

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.

The way in which toremifene works is not yet fully understood but its main function is as an anti-oestrogen drug. This means that it interferes with the action of the female hormone oestrogen.

Most breast cancers need supplies of the female sex hormone oestrogen to grow. Cancer cells have proteins called receptors on their surface that the sex hormones attach to. Cancers with oestrogen-receptors on the surface of their cells are called 'oestrogen-receptor-positive' (ER-positive) and toremifene is most effective against these cancers.

Under normal circumstances, when oestrogen comes into contact with the receptors it fits into them and activates the cancer cells to divide so that the tumour grows.

Toremifene imitates the action of oestrogen and fits into the receptor but does not activate the cells to divide. The toremifene remains in place and prevents oestrogen from reaching the cancer cells so that they either grow more slowly or stop growing altogether.

Toremifene is a tablet that is taken once daily. It should be taken at approximately the same time each day.

Each person's reaction to any medication is different. Many women who take toremifene have no side effects, while others will experience them. We have outlined the most common side effects so that you can be aware of them if they occur. However, we have not included those that are very rare, and which are therefore 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 the effects. This information should help you to discuss any queries about your treatment and its side effects with your doctor or nurse, as they are in the best position to help and advise you.

Some women may have some of the following:

Hot flushes and sweats Sometimes the flushes will gradually lessen over the first few months but some women continue to have them for as long as they take toremifene.

There are a number of ways to help to reduce or control hot flushes and sweats. Some women find it helpful to avoid or cut down on tea, coffee, nicotine and alcohol.

Recent research suggests that progesterone or some anti-depressants may be helpful in controlling this side effect. Your nurse or doctor can discuss this with you.

Some women find that complementary therapies help. Your GP may be able to give you details about obtaining these on the NHS.

Nausea and indigestion Feelings of sickness (nausea) and indigestion are fairly common but can often be relieved by taking your tablet(s) with food or milk or at night. Although nausea is quite common initially, it usually wears off after a few weeks.

Thrombosis (blood clots) This is very rare. Signs of a thrombosis include pain, warmth, swelling or tenderness in an arm or leg, or chest pain. Any of these signs must be reported to your doctor immediately.

Vaginal bleeding or discharge Let your doctor know if you have any vaginal bleeding or discharge.

Vision problems Blurred or reduced vision is again very rare but any visual changes should be reported to your doctor.

Tumour flare Women who are prescribed toremifene for advanced cancer, where it has spread to the bones, may experience something called tumour flare when they start taking toremifene. This can cause a raised level of calcium in the blood (hypercalcaemia) with symptoms of nausea, vomiting and thirst. Very occasionally, a short stay in hospital is necessary until the calcium levels have been reduced.

Studies have shown that women who take high doses of toremifene over a long period of time may have a very slightly increased risk of developing cancer of the lining of the womb (endometrial cancer).

However, this risk has to be weighed against the benefits of toremifene in treating the breast cancer, which generally far outweigh the small risk of womb cancer. If detected early, treatment for endometrial cancer is usually very successful. Early warning signs are abnormal vaginal bleeding – although this is often caused by non-cancerous conditions such as polyps. If you have any abnormal vaginal bleeding, you should let your doctor know.

However, this risk has to be weighed against the benefits of toremifene in treating the breast cancer, which generally far outweigh the small risk of womb cancer. If detected early, treatment for endometrial cancer is usually very successful. Early warning signs are abnormal vaginal bleeding – although this is often caused by non-cancerous conditions such as polyps. If you have any abnormal vaginal bleeding you should let your doctor know.

In some cancer hospitals, women are given regular gynaecological check-ups to detect signs of endometrial cancer. An ultrasound scan, using sound waves, may be done to check for signs of change in the womb lining. A small probe is inserted into the vagina and the doctor can look at the scan on a screen. Any changes can be seen straight away. The scan is safe and only takes a few minutes.

There is little doubt that for most women the beneficial effects of toremifene far outweigh the risks.

There is some evidence suggesting that while taking toremifene it can lower the level of fat or lipids in your blood (high levels of fat or lipids in the blood contribute to heart disease). It is thought possible that toremifene may be more effective than tamoxifen in helping to prevent heart disease. It is also thought that toremifene may help to prevent bone loss, which can reduce the risk of osteoporosis (thinning of the bone) in some women.

Toremifene 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 toremifene could harm them.
• Toremifene should be stored in its original packaging. It should be kept away from direct heat and light.
• 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 are sick just after taking the tablet tell your doctor, as you may need to take another one.
• 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 (54th edition). British Medical Association and Royal Pharmaceutical Society of Great Britain, September 2007.

For further references, please see the general bibliography.