The leading drug therapy for breast cancer can cause other types of cancers and should not be given to healthy women as a preventative drug, according to a review of tamoxifen research, writes Dick Ahlstrom, Science Editor.
Tamoxifen is in widespread use in Ireland by women who have been diagnosed with breast cancer. "It is a very good drug. It prolongs disease-free survival and is relatively non-toxic," explained Dr Serzgin Ismail of the University of Wales College of Medicine in Cardiff.
She publishes her review article on tamoxifen in the current issue of the Journal of Clinical Pathology.
It has been shown to keep breast cancer from recurring in women already diagnosed with the disease. Studies had indicated that the diagnosed patient was significantly better off for taking the drug. Tamoxifen also has known side effects, however. In particular it increases the risk of cancer of the womb.
Dr Ismail said that for this reason the drug should not be given to healthy women considered to be at high risk of contracting breast cancer.
Trials described in her report indicated that after taking the drug for two years the number of women developing cancer of the womb doubled, and after five years it quadrupled, compared with women not taking the drug.
"The problem really arises in women who are considered to have an increased risk of breast cancer," she said yesterday. Cancer of the womb can be very treatable.
"Nevertheless, being at risk doesn't mean you are going to get the disease. At the moment we know too little about [tamoxifen] to use it as a preventative drug."
There were 1,563 new cases of breast cancer diagnosed in Ireland in 1995, the latest year for which figures were available, according to the Irish Cancer Society. There were 649 breast cancer deaths during that year.
Tamoxifen is used in particular by post-menopausal women with the disease, explained Dr John Armstrong, the chairman of the society's medical committee. It is very effective and can prevent cancer spread in a high proportion of these cases, he said. "As such it saves a lot of lives."
The increased risk of womb cancer begins to outweigh the benefits of tamoxifen after longterm use, but patients with particular types of breast cancer would still benefit from its use even after five years.
There is an initiative in the US to have tamoxifen used as a preventative in high-risk women. Trials are underway to assess its potential. Dr Ismail expressed concern, however, that the risks would outweigh the benefits.