Tamoxifen and Breast Cancer Prevention

“Dr. B, is there a pill to prevent breast cancer? You know my sister has had breast cancer and she takes Tamoxifen. Does the pill prevent cancer in women who have had no breast cancer?”

As always, Susan’s questions are right to the point. She has read recent reports about the benefits of Tamoxifen in women with a significantly elevated risk factors. She wants to know where she stands.

Susan, let’s look at the history of Tamoxifen – it’s usage, side effects – and then review the results of recent study undertaken by the Breast Cancer Prevention Trial (BCPT).

Breast cancer is usually hormone (estrogen) dependent. When indicated, women with breast cancer underwent surgery to remove organs which produced estrogen (e.g. ovaries) which helped control or regress the tumor.

Discovery of Tamoxifen reduced the need for these surgical procedures as the drug stopped the binding of estrogen to the tumor. In 1977, Tamoxifen was approved in the U.S. by the Food and Drug Administration for use in breast cancer. Thus began a new era in the treatment of this cancer.

“Dr. B, why did the researchers think that Tamoxifen would help prevent cancer in women who have no personal history of breast cancer?”

Tamoxifen has been used for 21years in the treatment of breast cancer. During this time, it clearly showed that it can reduce the risk of recurrent breast cancer and development of cancer in the other breast. The later finding encouraged researchers to start Breast Cancer Prevention Trial.

“Go on Dr. B, how did they do the study?”

Susan, BCPT enrolled 13,388 women at 300 sites in U.S. and Canada. These women were at a higher risk of developing breast cancer. They were randomly assigned to receive either placebo or Tamoxifen

The study – over 6 years – showed 45 per cent reduction of breast cancer in women who took Tamoxifen compared to the placebo group. It was also observed that these women have lower incidence of osteoporosis and coronary artery disease. Because of this significant finding the trial was discontinued earlier than expected due to ethical reasons.

“Doctor, what are the side-effects of Tamoxifen?”

Susan, some women developed cancer of the uterus, some had deep vein thrombosis (blood clot in the leg), and some had pulmonary embolism (blood clot in the lungs). About 15 percent of women suffer from: hot flushes, irregular menstrual periods, nausea, vomiting, light-headedness and dizziness.

One significant unanswered question is: For how long a woman can take Tamoxifen without increasing the chance of side-effects?

Women with breast cancer have been advised not to take Tamoxifen for more than 5 years as the risk of recurrent cancer and death were higher in women who took Tamoxifen for 10 years. The same cannot be said for women who take this pill for prevention. The study wasn’t long enough.

“So, Dr. B, can a woman take Tamoxifen for prevention if she is not part of a clinical trial?”

Last year, Susan, Editorials in the British Medical Journal and the Canadian Medical Association Journal discouraged women taking Tamoxifen outside clinical trials until further information was available on its risks and benefits.

But the authors, who reported the BCPT results in the Journal of National Cancer Institute said: Despite side effects resulting from administration of Tamoxifen, its use as a breast cancer preventive agent is appropriate in many women at increased risk for the disease.

Susan was keen on exploring the idea further for preventive measures and was referred to a medical oncologist.

(This series of articles explore the health problems of Dave and his family. They are composite characters of a typical family with health problems)

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