The aim of hormonal therapy is to disrupt the supply of oestrogen capable of reaching the tumour cell and triggering a growth response.

In other words, the goal is to deprive the cancer cells of the hormonal stimulation they need to survive and grow.  Currently there are two main ways to achieve this.

Tamoxifen

One way to reduce the effect of oestrogen on tumour cells is to interfere with their ability to respond to it.  This can be done with a hormonal therapy designed to target the oestrogen receptors - specialised proteins on the cell surface that attach to the available oestrogen and relay its message to grow.  The best-known example of this is the drug tamoxifen.

Tamoxifen is often referred to an anti-oestrogen.  It works by directly competing with oestrogen to bind to oestrogen receptors on breast cancer cells.  By blocking the ability of these receptors to be stimulated to grow by oestrogen, tamoxifen has the effect of slowing the growth of the breast cancer cells.  A technical term for this is selective oestrogen receptor modulator.

This drug has now been used for over 20 years in the cases of advanced breast cancer  and more recently for early stage cancer and in cancer protection.  Recent studies have suggested a role for tamoxifen in preventing recurrence after breast surgery, whilst also hindering development of cancer in the opposite breast.

Two out of three breast cancers make the oestrogen and or progesterone receptor (receptor positive) and are considered hormone sensitive.  Whilst tamoxifen is thought to be most beneficial treating cancers shown to have oestrogen receptors, there is still some benefit with those cancers that are oestrogen receptor negative.

Whilst tamoxifen competes with oestrogen in breast cancers, it can also mimic the positive effects of oestrogen in other body systems.  Several studies suggest an age-related benefit.  Women over fifty may benefit from a reduced risk of heart disease and osteoporosis without having to take HRT. This may be related to oestrogen levels and the menopause.

Side effects of tamoxifen

There can be an increased risk of thrombosis and stroke and it is inadvisable to take tamoxifen if you have a history of uterine problems, blood clots, or cataracts.

Whether these side effects and added risks are acceptable or not will depend on whether the extent of the potential benefit that tamoxifen may have in treating your cancer outweighs these considerations.  Your cancer treatment team will take into account your medical history when discussing your treatment choices.

New treatments

Another new and potentially exciting way to manipulate oestrogen levels is to target oestrogen production itself. 

Although this can be achieved by targeting the production of oestrogen by the ovaries, there may now be the possibility of developing a treatment for post-menopausal women, where oestrogen production continues elsewhere.

After the menopause, most oestrogen is produced in fat and liver cells, where the aromatase enzyme helps to convert male hormones called androgens into oestrogen. 

Aromatase inhibitors, also called anti-aromatase compounds, reduce the blood levels of oestrogen in post-menopausal women by inhibiting the aromatase enzyme and hence oestrogen production.  

Preliminary studies with such compounds have indicated that they work well alongside tamoxifen and are associated with fewer side effects.

02/06/2009