Tamoxifen

Tamoxifen Back to top

Tamoxifen is an anti-oestrogen drug that was developed over 30 years ago. It is used widely to treat breast cancer and is occasionally used to treat some other cancers.

Tamoxifen can also be used to treat or prevent side effects of breast tenderness and swelling in some men with prostate cancer . These side effects can happen as a result of other hormonal treatments.

How it works Back to top

The way in which tamoxifen works is quite complicated and not yet fully understood. Its main function is as an anti-oestrogen drug.

Many breast cancers rely on the female sex hormone oestrogen to grow. Hormone-sensitive breast cancer cells have proteins called receptors that the sex hormones attach to. They are known as 'oestrogen-receptor positive' (ER-positive) breast cancers. When oestrogen comes into contact with the receptors, it fits into them and stimulates the cancer cells to divide so that the tumour grows.  

Tamoxifen fits into the oestrogen receptor and blocks oestrogen from reaching the cancer cells. This means the cancer either grows more slowly or stops growing altogether.

How it is taken Back to top

Tamoxifen is a tablet that should be swallowed whole with a glass of water. The tablets come in different strengths: 10mg, 20mg and 40mg.

The drug is manufactured under several different brand names and these may appear on the tablets. It's also available as a sugar free syrup for people who have difficulty swallowing tablets.

Tamoxifen is usually prescribed as a single daily dose and this should be taken at the same time each day.

You may prefer to take the tablet with food as it may make you feel sick and can leave a metallic taste in your mouth. It's best to find a convenient time for you and stick to it.

When it may be given Back to top

Your doctor will take into account a number of different factors when planning your treatment. The breast cancer cells will be tested to see if they have have oestrogen receptors (ER) and progesterone receptors (PR). Tamoxifen is only effective for people who have hormone-sensitive breast cancers.

Tamoxifen may be given after surgery for early breast cancer, to reduce the risk of the cancer coming back. This is known as adjuvant therapy.

You may be given tamoxifen for five years. Some people may have tamoxifen for two or three years and then change to a different type of hormonal therapy known as an aromatase inhibitor. Aromatase inhibitors include anastrozole| (Arimidex®), exemestane| (Aromasin®) and letrozole| (Femara®).

Occasionally tamoxifen is used before surgery, to shrink a large breast cancer. This means that a lumpectomy (removal of the lump) may be possible, rather than removal of the whole breast (a mastectomy).

Tamoxifen can also be used to control a cancer that has come back or spread to other parts of the body.

Preventative treatment Back to top

Research has been carried out to see if tamoxifen can prevent breast cancer in women who have a high risk of developing the disease. 'High risk' is defined as having one or more close relatives (mother or sister) who had breast cancer before they were 50.

The results from some research trials show that tamoxifen helps to prevent ER-positive breast cancers in high risk women, but not ER-negative breast cancers. Other trials are still ongoing.

If you think that a member of your family may be at high risk of breast cancer, they should discuss the possible monitoring and treatment options with their doctor.

Possible side effects Back to top

Each person's reaction to any medicine is different. Some people have very few side effects while others may experience more. Very rarely, if the side effects are severe, you may have to stop taking tamoxifen and a different drug may be prescribed.

You may have some of the following side effects, to varying degrees: 

• Hot flushes and sweats These are a common side effect of tamoxifen. They may gradually lessen over the first few months but some people continue to have them for as long as they take tamoxifen. There are a number of ways to help reduce or control hot flushes and sweats. Some people find it helps to avoid or cut down on tea, coffee, nicotine and alcohol. Research suggests that some types of antidepressants may be helpful in controlling this side effect. Your doctor or nurse can discuss this with you.
  Some people may find complementary therapies such as acupuncture helpful. Your GP may be able to give you details about having these on the NHS. If you find your own complementary therapist, make sure that they are properly qualified and registered.
  If the hot flushes are really troublesome, you can discuss possible treatments with your doctor. They may be able to prescribe a different hormonal therapy instead.
  Sometimes the hot flushes continue for a long time after you have stopped taking tamoxifen.
  You can read more about treatments for menopausal symptoms like hot flushes in our information about Breast cancer and menopausal symptoms.
• Nausea and indigestion Feeling sick (nausea) and indigestion are fairly common, but can often be relieved by taking your tablets with food or milk, or at night. Although nausea is quite common initially, it usually wears off after a few weeks.
• Weight gain Some women notice that they put on weight while taking tamoxifen. This may be due to water retention.
• Change in periods Women who have not yet reached the menopause may notice that their monthly periods change – they may become irregular, lighter or sometimes stop altogether. Some women also notice an increase in vaginal discharge and itching of the area around the vagina (the vulva).
• Leg cramps Some women get leg cramps with tamoxifen. Walking may stretch the muscle and help with this. Let your doctor know if leg cramps are a problem. If your leg becomes red, hot or swollen (see blood clots, below), tell your doctor immediately.

Less common side effects Back to top

• Depression, tiredness and dizziness Some women feel depressed while taking tamoxifen, but this may be due to other causes.
• Headaches Some people affected by migraine notice a change in the pattern of their headaches.
• Blood clots (thrombosis) In post-menopausal women, tamoxifen can slightly increase the risk of blood clots and strokes. If you have any pain, warmth, swelling or tenderness in an arm or leg (or any chest pain), you must tell your doctor straight away.
• Vision problems Blurred or reduced vision is very rare, but any changes in your eyesight should be reported to your doctor.
• Voice changes This has been reported by some people. Professional singers may want to seek help and advice from their doctor.
• Tumour flare People who are prescribed tamoxifen for cancer that has spread to the bones, may experience something called tumour flare when they start taking tamoxifen. 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 needed until the calcium levels have been reduced.
• Rare side effects of tamoxifen These may include mild allergic reactions, such as skin rashes and hair loss (this will grow back later).

Always let your doctor or nurse know about any side effects you have. There are usually ways in which they can be controlled or improved.

Long-term side effects Back to top

Studies have shown that post-menopausal women who take tamoxifen 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 small risk is generally outweighed by the benefits of taking tamoxifen.

If detected early, treatment for endometrial cancer is usually very successful. An early warning sign is abnormal vaginal bleeding, although this is often caused by a non-cancerous condition such as polyps. If you have any abnormal vaginal bleeding you should let your doctor know. Some women may have regular gynaecological check-ups.

Additional information Back to top

• Contraception Tamoxifen should not be taken during pregnancy as it may harm the developing baby. Although it can affect a woman's periods, tamoxifen is not a contraceptive. It's important to use an effective, non-hormonal form of contraception during treatment.
• Fertility Women who haven't been through their menopause may still become pregnant when they've finished treatment with tamoxifen. Doctors usually advise you to wait for a few months after tamoxifen treatment is over before you try to get pregnant. Talk to your doctor first if you are thinking of getting pregnant.
• Risk of blood clots If you have a history of blood clots or deep vein thrombosis (DVT) let your doctor know, as tamoxifen may not be suitable for you.
• Interaction with warfarin Tamoxifen can increase the effect of the drug warfarin, which is used to thin the blood in people prone to blood clots. If you are taking warfarin, let your doctor know straight away.
• CYP2D6 inhibitors There is some research that suggests some drugs - including the antidepressants paroxetine (Seroxat®) and fluoxetine (Prozac®) - may cause tamoxifen to be less effective, but this isn't certain. Tell your doctors about any other medicines you are taking. 
• Bone loss Tamoxifen may help to prevent bone loss in women who have been through their menopause. In some women it may reduce the risk of thinning of the bone (osteoporosis).
• Heart disease Tamoxifen can lower the level of fat (lipids) in your blood (high levels of fat contribute to heart disease). But research doesn't show that tamoxifen reduces the risk of heart disease.

Things to remember about tamoxifen tablets Back to top

• Tamoxifen may interact with other medicines. Tell your doctor about any medicines you are taking, including non-prescribed drugs such as complementary therapies, vitamins and herbal drugs.
• Keep the tablets in a safe place, out of reach of children.
• Keep the tablets in the original packaging/container and store them at room temperature, away from moisture, direct heat and sunlight.
• Store the tablets in the original packaging/container. They should be kept at room temperature, away from moisture and direct heat.
• 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. 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 have plenty for holidays.

References Back to top

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

• Sweetman et al. Martindale: The Complete Drug Reference. 36th edition. 2009. Pharmaceutical Press.
• British National Formulary. 59th edition. 2010. British Medical Association and Royal Pharmaceutical Society of Great Britain.
• Uptodate www.uptodate.com/online/index.do (accessed September 2010)
• electronic Medicines Compendium (eMC). www.medicines.org.uk (accessed September 2010)
• Kelly CM, et al. Selective seratonin reuptake inhibitors and breast cancer mortality in women receiving tamoxifen: a population based cohort study. BMJ. 2010. 340: c693.  

For further references, please see the general bibliography|.