What is Tamoxifen?
Tamoxifen is a hormonal therapy that blocks the effects of oestrogen in breast tissue. Developed more than 20 years ago, it is widely used to treat breast cancer, both after the initial surgery and if the cancer has come back following treatment. Tamoxifen may also be used to help prevent breast cancer in some women who are at very high risk of developing the disease.
Effect of oestrogen in the body
Women’s bodies produce two female sex hormones called oestrogen and progesterone. Women’s ovaries begin producing these hormones at puberty and continue to do so until menopause. Following menopause, the ovaries cease their production, but small amounts of oestrogen continue to be produced in other tissues. These hormones travel through the bloodstream and target the cells in a number of different organs. The breast and uterus are the two organs most
significantly affected, but oestrogen also acts on the brain, bone, liver and heart. During a woman’s reproductive years, a normal function of oestrogen is to trigger the proliferation of cells that form the inner lining of the milk glands each menstrual cycle, in preparation for a possible pregnancy. However, this increased cell proliferation is accompanied by an increased risk of abnormal cell changes, which may later develop into cancer. These cancer cells may themselves be stimulated to grow and reproduce by oestrogen.
How Tamoxifen works
Tamoxifen binds onto the oestrogen receptors of breast cells, which then prevents the oestrogen molecules from doing so. Oestrogen is therefore unable to stimulate the proliferation of breast cells, including cancer cells.
Who can benefit from Tamoxifen?
Although tumours that are found to have oestrogen receptors are usually the more responsive to Tamoxifen, it may provide some effect, though probably much less effect, in some instances where the test does not show any oestrogen receptors. The presence of progesterone receptors, in the absence of oestrogen receptors, may also be an indicator that the cancer will respond to Tamoxifen.
Therefore each woman’s case will be considered individually, as anticipated benefits of treatment for her must be weighed against possible side-effects. Tamoxifen is commonly used in addition to other treatments such as surgery, radiation therapy and chemotherapy, to reduce the chance of the cancer returning in the same breast and the development of new cancers in the opposite breast. It may also be used to control breast cancer that has returned after initial treatment. In these circumstances, it can often control cancer for long periods of time. Women who have been identified to be at very high risk of developing breast cancer may benefit from using Tamoxifen as a preventative measure.