This information is about a hormonal therapy called diethylstilbestrol, which is also commonly called Stilboestrol®. It is used to treat prostate cancer. The information should ideally be read with our general information about prostate cancer.

Stilboestrol is a man-made drug similar to the female hormone oestrogen. It is used in the treatment of advanced prostate cancer, where the cancer has spread beyond the prostate gland – for example, to the bones.

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.

Many prostate cancers need supplies of the male hormone testosterone to grow. Most testosterone is produced by the testes and in small amounts by the adrenal glands.

Stilboestrol reduces the level of testosterone in the body by making the brain think there are too many sex hormones circulating in the body. When this occurs, production of testosterone is 'switched off'. This reduced level of testosterone can help to slow down the growth of the cancer cells and may cause the cancer to shrink in size.

Stilboestrol is a tablet which is taken once a day, ideally at the same time each day.

Each person's reaction to any medicine is different. Many people have very few side effects with Stilboestrol, while others may experience more. We have outlined the most common ones. However, we have not included those that are very rare and 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, who are in the best position to advise you. Let your doctor know if you have had heart or liver problems, as stilboestrol may slightly affect your heart and liver function.

The following side effects can sometimes occur:

Blood clots (thrombosis) Stilboestrol can increase the risk of getting a blood clot. Let your doctor know immediately if you have any pain, warmth, swelling or tenderness in an arm or leg, or any chest pain. Some doctors may prescribe a low dose of aspirin while you are taking Stilboestrol to help prevent blood clots. It's important not to take drugs that contain aspirin unless they have been prescribed by your doctor.

Fluid retention Some people may have ankle swelling caused by fluid retention. This is not harmful but can be uncomfortable.

Breast tenderness or fullness Some men may notice slight breast swelling and tenderness. Your doctor can prescribe medication to reduce any discomfort.

Loss of sex drive (libido) and erection difficulties (impotence) If this occurs it may return to normal after stopping the drug, unless you are also taking another type of hormonal therapy. Your doctor or nurse can discuss this with you.

Tiredness You may feel tired and lacking in energy while taking Stilboestrol.

Feeling sick (nausea) and being sick (vomiting) This is usually mild and can be easily controlled. Nausea can sometimes be relieved by taking the tablet with food. Let your doctor know if you have any of these side effects, as they can prescribe medicines to help.

Weight gain Weight gain can be a side effect of Stilboestrol. This is often due to water retention, which is not harmful but can be uncomfortable.

Headaches Some people have headaches whilst taking Stilboestrol but this is not common. It is important to drink plenty of fluids. Let your doctor know if you have headaches as medicines can be prescribed to help.

Hair thinning Some men notice that their hair becomes thinner while taking Stilboestrol. This is usually mild and the hair will regrow at the end of treatment.

Skin changes Rarely, Stilboestrol can cause skin rashes and/or darkening of the skin.

Your doctor will discuss the length of treatment that they feel is appropriate for your situation. Stilboestrol is often given for several months or even years. Treatment may continue for as long as it is effective in controlling your cancer.

• Keep the tablets in a safe place out of the reach of children, as Stilboestrol 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.
• Don't worry if you forget to take your tablet. Do not take a double dose. 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 you that 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.
• electronic Medicines Compendium (eMC) emc.medicines.org.uk (accessed 25 November 2008)

For further references, please see the general bibliography.