A recent breast cancer prevention study by The National Surgical Adjuvant Breast and Bowel Project showed that the anti-estrogen agent, tamoxifen, decreased the incidence of invasive breast cancer in women who were at high risk for developing this disease. This finding appears to suggest a potentially promising role for tamoxifen in preventing breast cancer in some persons.
Breast cancer is the second leading cause of cancer deaths in women in the United States. However, recent progress in the areas of cancer screening and treatment holds promise for earlier detection and higher cure rates. The term
screening refers to the regular use of certain examinations or sensitive tests (such as mammograms) in persons who do not have any symptoms of a cancer but are at high risk for a cancer. When a person is at
high risk for breast cancer, this means that she has certain characteristics or exposures, called
risk factors, that make her more likely to develop breast cancer than those who do not have these risk factors. Risk factors that have been suggested in association with breast cancer include: older age, early age at first menstrual cycle, late age at the birth of the first child, having had breast cancer before, having had breast cancer in the family (mother or sister) before, having had other diseases of the breast, and using estrogen replacement therapy.
Tamoxifen is an anti-estrogen agent that is sometimes used postoperatively to treat breast cancer that is
hormone receptor-positive (cancer cells that use hormones, such as estrogen, to help them grow). A recently published report indicated that tamoxifen might also be effective in helping to prevent some breast cancers.
Researchers evaluated 13,388 women who were at high risk for developing breast cancer. The women either: 1) were 60 years of age or older; 2) had previously had
lobular carcinoma in situ (abnormal, noncancerous cells in the breast that are associated with an increased risk for developing breast cancer later); or 3) were 35 to 59 years of age and had risk factors that increased their risk for breast cancer to at least 1.66%. The women were assigned to receive either tamoxifen or placebo daily for 5 years. The results showed that tamoxifen reduced the overall risk for
invasive breast cancer (cancer that has spread outside the immediate area of the breast in which it originated) by 49%, compared with placebo. Women 49 years of age or younger had a 44% decrease, women 50 to 59 years had a 51% decrease, women older than 60 years had a 55% decrease, and women having had lobular carcinoma in situ had a 56% decrease in the incidence of invasive breast cancer. Tamoxifen was also associated with a reduction in the incidence of
noninvasive breast cancer by 50%. All decreased incidence of breast cancer occurred in cases of hormone receptor-positive cancers (69% decrease overall); no effect was observed on hormone receptor-negative cancers. Tamoxifen did have some potential adverse effects, including an increased incidence of cancer of the
endometrium (lining of the uterus, or womb) and elevated rates of stroke and pulmonary embolism, mainly in women 50 years and older.
These findings suggest that the use of tamoxifen decreases the risk for developing invasive and noninvasive breast cancer, and may play a valuable role in preventing breast cancer in some women who are at high risk for this disease. Women who are at high risk for developing breast cancer may wish to talk with their doctor about the risks and benefits of participating in a clinical trial in which tamoxifen or other promising new therapies are being studied. Two sources of information on ongoing clinical trials that can be discussed with a doctor include a comprehensive, easy-to-use service provided by the National Cancer Institute (cancer.gov) and the Clinical Trials section and service offered by Cancer Consultants.com (www.411cancer.com). (Journal of the National Cancer Institute, Vol 90, No 18, pp 1371-1388, 1998)
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