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Tamoxifen is a synthetic hormone that has long been established as a treatment for women with beast cancer. It is of benefit when used in post-menopausal, as well as women who are pre-menopausal or under the age of 50. In most cases, it is prescribed as an adjuvant treatment, which means that it is given in addition to surgery. It is usually used alongside chemotherapy and radiotherapy.

In specific cases, tamoxifen is used as a first line treatment in breast cancer to try to shrink the tumour to make it smaller. Surgery could possibly then be less extensive. You may consider being part of a clinical trial that addresses this concept in a research setting such as IMPACT (if you are part of this study, a separate leaflet is available).In some frail elderly women, it may be useful to try tamoxifen to treat breast cancer to avoid surgery altogether.

The normal dose of tamoxifen is 20 mg per day and is used for 5 years as an adjuvant treatment in breast cancer. The benefits of tamoxifen are greatest in women whose breast cancers are oestrogen receptor positive. Tamoxifen reduces the risk of breast cancer recurring not only in the treated breast, but also elsewhere in the body and in the contralateral (opposite) breast. Tamoxifen is known to reduce the risk of breast cancer returning by 30% and in contralateral tumours by 50%.

In pre-menopausal women, there has recently been evidence that tamoxifen combined with a gonadotrophin releasing hormone analogue such as goserelin (Zoladex) may confer additional benefits. The research so far does not show that this translates to better survival, but it is likely to demonstrate this when the women studied are followed up for longer.

Mechanism of action:
Tamoxifen is considered to be an oestrogen antagonist and therefore acts on oestrogen receptors in breast cancer to prevent cell function. There is also an effect on the pituitary gland that may result in an increased secretion of oestrogen in pre menopausal women. Tamoxifen does not stop your body making oestrogen, but instead has an effect on blocking any cancer cells that use circulating oestrogen.

Tamoxifen does not only act by blocking oestrogen receptors, and its anti-cancer function is also effected through other chemicals that are known to block stimulation or enhance inhibition of tumour growth. Tamoxifen reduces the level of cholesterol in the blood thus reducing the risk of heart disease and blockage of the arteries. It is also helpful in preventing osteoporosis, in post-menopausal women.

Side effects of tamoxifen:
Like any medicine there are potential side effects of tamoxifen. The actual side effects experienced differ between individuals but most women tolerate tamoxifen extremely well. The most common side effects reported by women on tamoxifen are similar to that induced by the menopause.

• Hot flushes and sweats are usually mild but some women find these distressing Should this occur, there are measures that can be taken to reduce this inconvenience. Many women find it helpful to wear clothing that can be removed easily, or to carry a small fan, or moist wipes to use during a flush. In addition non hormonal medication such as Evening Primrose Oil or clonidine can be used. Sometimes, additional progesterone also helps.

• Irregular or stopping periods. If you are pre menopausal, you may develop a change in your periods. Should you be approaching your menopause, your periods might stop altogether. However as many women also have adjuvant chemotherapy to treat breast cancer it is difficult to separate whether cessation of periods occurs as a result of the chemotherapy or tamoxifen.

• Vaginal discharge is reported by approximately 10% of pre menopausal women and 25% of postmenopausal women. This is related to a change in the environment of the genital tract and should not cause concern unless there is any unusual bleeding. As tamoxifen is also an anti oestrogen some women report genital irritation or dryness. Soreness and discomfort during sexual intercourse may be help by a lubricant such as Replens that is available from pharmacists without prescription.

• Thinning of the hair, brittle nails and dryness of the skin have been reported by women on tamoxifen.

• Occasionally, tamoxifen induces gastrointestinal disturbance such as indigestion or nausea. These may be helped by taking the tablets with food or at a different time such as in the evening.

• Weight gain; As tamoxifen influences fluid retention and redistribution of fat, there may be weight gain during the course of treatment. Weight gain may, however, also occur during cancer treatment as a result of changes in lifestyle, altered diet, reduction in exercise or even as a result of chemotherapy.

Rare side effects
• Fibroids in the womb and ovarian cysts. This is more common in women who are pre or peri menopausal.

• Thickening of the endometrium.. The usual cause of this is a benign reaction to the oestrogen component of tamoxifen. Any form of vaginal bleeding must be reported immediately. Very rarely, endometrial cancer may arise in women who have been taking tamoxifen. Endometrial cancer is uncommon in the U.K. at an incidence of about 3 cases per 10,000 women. Tamoxifen increases this risk three or four fold.

• There is a small increase of venous thrombosis (blood clot). This risk is high if you have previously had a thrombosis in your veins

• Blurring of vision is rare.

• Professionals who use their voice (for example on the stage) have reported voice changes, but most women do not notice any difference.

• Drugs interactions. The most important of these is warfarin and you may need more frequent blood checks to get the warfarin dose correct.

The use of tamoxifen in women with advanced breast cancer
Most women treated with tamoxifen are known to be ER positive. You may notice that your general illness gets slightly worse before it gets better. It could also temporarily increase the serum calcium in your blood. If on starting tamoxifen you feel unwell, thirsty or notice an increase in pain, you must report this immediately, as a significant rise in calcium needs hospital treatment.

Tamoxifen to treat breast pain
In women with severe breast pain a short, three months course with tamoxifen sometimes helps control symptoms. Although some of the more common side effects may be experienced during the course of treatment, dangerous side effects such as spontaneous blood clots in the vein or endometrial cancer are unlikely because of the short duration of treatment.

Tamoxifen and pregnancy
Tamoxifen is not a contraceptive and you should use alternative contraception such as the condom. You should not use the oral contraceptive pill. The effect of tamoxifen on the developing foetus is unknown. Normal pregnancy is possible upon completion of your treatment with tamoxifen, provided your ovaries and reproductive tract is functioning normally.

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