(GENOX)
What is tamoxifen?
Tamoxifen is an anti-oestrogen drug (designed to counteract the effects of oestrogen). It was developed over 20 years ago and is now used widely to treat breast cancer, both after the initial operation and if the cancer has come back after treatment. It is also used to treat a variety of other conditions, including infertility.
How it is taken?
Tamoxifen is taken as a tablet. It comes in different strengths: 10mg, and 20mg. The drug is also manufactured under different brand names and these may appear on the tablets. It is also available as a sugar-free syrup for people who have difficulty swallowing tablets.
How it works?
The way that tamoxifen works is quite complicated and not yet fully understood, but its main function is as an anti-oestrogen drug. This means that it reduces or stops the action of the female hormone, oestrogen.
In order to grow, many breast cancers rely on supplies of
sex hormones, particularly oestrogen. On the surface of the cancer cells are proteins
called receptors. Cancers with oestrogen receptors on the surface of their
cells are called `oestrogen receptor positive' (ER positive) and tamoxifen can
greatly reduce the chance of these cancers coming back after surgery, and can
also shrink large tumours down so that they can be removed.
The easiest way to understand how tamoxifen works is to
liken the process to that of a lock and key. The receptors are the lock and the
female sex hormones are the keys. When the sex hormones come into contact with
the receptors they unlock or activate the cancer cells to divide, and the
tumour grows. Tamoxifen imitates the action of the sex hormones and fits into
the lock but the key does not turn and the cells do not divide. The tamoxifen
keys remain in place and prevent the oestrogen from reaching the cancer cells
so they either grow more slowly or stop growing altogether.
Preventive treatment
Research is currently being done 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, sister) who had breast cancer before they were 50. The results of some trials are available, but others 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
Because people react to drugs in different ways, it is impossible to predict who is going to have side effects. Many women who take tamoxifen have no side effects at all, while others will experience them.
Very rarely, if side effects are severe, you may have to
stop taking tamoxifen and a different drug may be prescribed.
Side effects are more common in pre-menopausal women, who
may develop menopausal side effects as a result of a lowered level of
oestrogen. The most common side effects, apart from nausea, are hot flushes and
sweats, particularly at night.
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 tamoxifen. If you are having troublesome hot flushes
do not hesitate to discuss possible treatments with your doctor. Your doctor
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.
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.
Weight gain. Some women notice that they gain weight while taking
tamoxifen and 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
(vulva).
Less common side effects
Depression, tiredness and dizziness. Some women feel depressed while taking tamoxifen but this may be due to other causes.
Very rare side effects of tamoxifen include:
Mild allergic reactions this may include skin rashes.
Temporary thinning of the hair.
Headaches some people affected by migraine have noticed a
change in the pattern of their headaches.
Thrombosis (blood clots) pain, warmth, swelling or
tenderness in an arm or leg or any chest pain must be reported to your doctor
immediately.
Visual problems blurred or reduced vision is again
very rare but any visual changes should be reported to your doctor.
Voice changes have been reported by some women professional
singers may want to seek help and advice.
Rarely, women who are prescribed tamoxifen for advanced
cancer, where there has been spread to the bones, may have 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 necessary
until the calcium levels have been reduced.
Is tamoxifen safe for everyone to take?
Like most drugs, tamoxifen should not be taken during pregnancy. Even though it can affect a woman's periods, tamoxifen is not a contraceptive, so reliable contraception must be used.
Tamoxifen can increase the effect of the drug warfarin, that
is used to thin the blood in people prone to blood clots. If you are taking
warfarin let your doctor know straight away.
Long-term side effects
Tamoxifen studies have shown that women who take high doses
of 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 risk has to be weighed against the benefits of tamoxifen in
treating the breast cancer, which generally far outweigh this small risk.
If detected early, treatment for endometrial cancer is
usually very successful. Early warning signs are abnormal vaginal bleeding,
although this is often caused by a non-cancerous condition such as polyps. If
you do 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 tamoxifen far outweigh the risks.