I haven't had breast cancer. Should I take Tamoxifen to reduce my risk?
Tamoxifen have been shown to lower the chance of breast cancer occurring by around 30%. However, it has to be taken daily for 5 years and has side effects. This article may help you have an informed discussion with your breast specialist and will hopefully answer many of your questions.
Note: Tamoxifen is also used to treat breast cancer. The benefits of taking Tamoxifen to prevent a metastatic recurrence is quite different.
Should I take Tamoxifen?
Things to think about include:
- Your breast cancer risk
- How you feel about that risk
- How you feel about taking a tablet every day for 5 years, especially if it has risks and side effects
- Your personal medical history
- Your current age
Breast Cancer Risk
Breast cancer is common. A woman whose mother (or whose grandmother and aunt) had breast cancer is considered to be at average risk, if the women were over 50 and there are no high risk features such as ovarian cancer in the family or Jewish heritage.
Your breast cancer risk depends on your own history, your family history, your age and some other factors including your heritage.
The reduction in risk is relative
That means that the benefit depends on your risk. For example, let’s consider a relative reduction in risk of 30%.
If your risk is average, (say 9% over your lifetime), then your risk will be reduced by 3%. The side effects may outweigh the benefit.
If your risk is moderate (say 15 to 30% over your lifetime), then your risk would be reduced by 5 or 10% with a residual risk of 10 to 20%. Some women would trade some side effects for this level of benefit.
If your risk is high due to an inherited cancer syndrome (maybe 75% over your lifetime), then your risk would be reduced to 50%. For a woman in her 30s or 40s, this may still seem too high. She may prefer to have bilateral mastectomies, reducing her risk to less than 1 or 2%.
What are Tamoxifen's side effects?
- menopausal symptoms such as hot flushes, night sweats and vaginal dryness
- increased risk of a blood clot or stroke, especially if you have high blood pressure or smoke
- increased the chance of cancer of the uterus, although the risk is low in young women
- it is believed to be teratogenic (damages a developing foetus)
- Women who are pregnant, breast feeding or planning on becoming pregnant soon
- Women who have a history of blood clots (eg in the legs or the lungs) or stroke.
What else can I do to reduce my risk of cancer?
Population studies have shown that the risk of cancer can be reduced by as much as 30%by
- Following a healthy diet, high in fruit and vegetables and low in processed foods
- Exercising moderately for 20 minutes a day
- Maintaining a healthy body weight.
- Not smoking
- Not drinking or limiting drinking to one drink, less than 5 times a week
What to do next?
Discuss your family history with your breast specialist. They will be able to help you decide if these medications are right for you. They are also the ones who will be organising your breast screening.
How does Tamoxifen work?
Tamoxifen effects how the oestrogen receptor works
Oestrogen (like the male hormone testosterone) is a growth hormone. Oestrogen is made in the ovaries before menopause and in the body fat in men and post-menopausal women. The oestrogen travels through the blood and enters cells via the oestrogen receptor.
Not all cells have oestrogen receptors and not all oestrogen receptors are the same. Oestrogen receptors are common in the breast, the bone, the heart and the female reproductive organs such as the uterus, vagina and ovary.
Tamoxifen effects these receptors differently. That is why Tamoxifen is called a Selective Oestrogen Receptor Modulator (a SERM).
- It blocks receptors in the breast, the vagina and the brain (so it can cause menopausal side effects like hot flushes, night sweats and depression)
- It doesn't affect the receptors in the bone (so it doesn't cause osteoporosis)
- It stimulates receptors in the uterus (which is why it increases uterine cancer risk).
Tamoxifen was actually developed as a fertility drug as it stimulates ovulation. It's very important to use a non-hormonal form of birth control while using Tamoxifen to prevent pregnancy as Tamoxifen is teratogenic (it damages a growing foetus).
How do we know it reduces breast cancer risk?
When the initial studies were done using Tamoxifen to treat breast cancer two effects were seen. Women taking Tamoxifen were:
- more likely to be cured.
- less likely to get a contralateral breast cancer (that is a new breast cancer in the other breast)
Because of these results, trials were conducted to see women who were at high risk of breast cancer could reduce their risk. These studies showed that Tamoxifen could reduce the risk by around 30% if taken for 5 years. And we now know that the benefit last for at least 20 years.
What Tamoxifen cannot do
Tamoxifen does prevent every women that takes it from getting breast cancer. It only prevents 1 in 3 breast cancers.
Also, while Tamoxifen reduces the risk of getting breast cancer, it has not been shown to lower the risk of dying from breast cancer. That is because breast cancer screening is very good and often (but not always) catches breast cancers early and because breast cancer treatments such as chemotherapy and radiotherapy are very effect (but certainly not perfect) at treating breast cancer. In Australia today the number of women diagnosed with breast cancer who live for at least 5 years is 91% (and it is 96% if the cancer was confined to the breast).
Tamoxifen doesn't reduce the risk of getting HER2 positive or triple negative breast cancer. It only reduces the risk of getting ER+ breast cancer.