Breast cancer: Horomone replacement therapy and cancer risk

Hormone replacement therapy (HRT) is used to relieve menopause symptoms, especially hot flushes. A woman on hormone therapy usually takes both oestrogen and progestogen (typically a synthetic form of progesterone). Women who have had a hysterectomy can take oestrogen alone. Oestrogen relieves hot flushes and prevents osteoporosis, but oestrogen can increase your risk of developing uterine cancer. Progestogen is added in women with a uterus to prevent this.

Many studies have looked at the association between hormone therapy and breast cancer. The best evidence for the benefits and risks of hormone replacement therapy come from the US Women's Health Initiative (WHI), a large study involving more than 16,000 healthy women. The results published in July 2002 showed that the risks of combined HRT of oestrogen plus progestogen outweigh the benefits. These risks include an increase in breast cancer, heart disease, stroke and blood clots.

Not only does combined HRT increase the risk of developing breast cancer, but it also increases the chances that the cancer will be discovered at a more advanced stage. This is due to its influence in reducing the effectiveness of mammography.

If a woman no longer has a uterus, oestrogen alone can be given for symptoms of menopause. This probably does not increase the risk of developing breast cancer much, if at all. In March 2004 it was concluded from the WHI study that those taking only oestrogen had no increased risk of breast cancer or heart disease, however oestrogen does appear to increase one's risk of stroke.

If a woman is faced with menopause and hot flushes, she and her doctor should discuss the risks and benefits and decide if treatment should included hormone therapy or not.

Do the benefits of hormone therapy outweigh the risk?

Hormone therapy is an effective treatment for relieving hot flushes from menopause. However the known link between hormone therapy and increased breast cancer risk has discouraged many women and their doctors from choosing or recommending this treatment.

The type of hormone therapy (oestrogen only or combination of oestrogen and progestogen), as well as the woman's individual characteristics, risk factors and severity of menopause symptoms, should be considered when weighing the risks and benefits of HRT. The decision to use hormone therapy after menopause should be made by a woman and her doctor after weighing all of the potential risks (including heart disease, breast cancer, stroke and blood clots) and benefits (relief of menopause symptoms and prevention of osteoporosis).

The known association between HRT and breast cancer has prevented many breast specialists from recommending it for breast cancer survivors. Unfortunately many women experience menopause symptoms after breast cancer treatment. Some forms of chemotherapy can also cause early menopause in premenopausal women.

In the past doctors had offered HRT after breast cancer treatment because there weren't clear-cut studies to show that it did any harm. However in 2004 a US study (the HABITS study) was stopped early after it was shown that cancer survivors on HRT were more likely to develop a new or recurrent breast cancer. Doctors now feel it may be too risky to treat breast cancer survivors with HRT.