However treatment with high doses of chemotherapy is very toxic, and sometimes fatal. The treatment is still regarded as highly experimental - there is no evidence yet to say whether or not the benefits outweigh the risks. Tamoxifen Tamoxifen is a drug which blocks the effect of oestrogen on cells. It is not a form of chemotherapy. It is thought that in some women, mainly those who have plenty of oestrogen receptors, oestrogen is driving the cancer to grow.
Tamoxifen blocks the effect of oestrogen on the cell, so it blocks the drive to grow.
In most cases, the cancer stops growing, even though it does not kill the cancer cells. It still works in women with ER-negative tumours, although to a lesser degree. There is evidence to suggest that women taking tamoxifen for long periods, such as five years, receive more benefit than women taking it for shorter periods, such as two years. The most common side effects from tamoxifen are hot flushes, vaginal dryness and vaginal discharge. Very rarely, it also causes eye problems.