Breast Cancer Prevention Studies

Breast Cancer Prevention

Breast Cancer Prevention

( — Breast cancer prevention studies are clinical trials (research studies conducted with people) that explore ways of reducing the risk, or chance, of developing breast cancer. Prevention studies usually involve women who have not had breast cancer, but are at high risk of developing the disease. Through such studies, scientists hope to determine what steps are effective in reducing the risk of breast cancer in women of all races and ethnic backgrounds.

Most breast cancer prevention research is based on evidence linking the development of this disease, in many cases, with exposure to the hormone estrogen. The focus of several recent breast cancer prevention studies has been on testing the effectiveness of drugs called selective estrogen receptor modulators (SERMs). SERMs are drugs that have some anti-estrogen properties and some estrogen-like properties. Their anti-estrogen activity may help reduce the risk of breast cancer by blocking the effects of estrogen on breast tissue. Their estrogen-like properties may help prevent the loss of bone density in postmenopausal women; however, SERMs may cause bone loss in premenopausal women.

The Breast Cancer Prevention Trial (BCPT)

The Breast Cancer Prevention Trial (BCPT) was funded by the National Cancer Institute (NCI) and conducted by the National Surgical Adjuvant Breast and Bowel Project (NSABP). The BCPT was designed to see whether tamoxifen (Nolvadex), a SERM, can prevent breast cancer in women who are at an increased risk of developing this disease. The study began recruiting participants in April 1992 and closed enrollment in September 1997. This study involved 13,388 premenopausal and postmenopausal women at more than 300 centers across the United States and Canada.

Results showed 49 percent fewer diagnoses of invasive breast cancer in women who were randomized to take tamoxifen compared with women who were randomized to take a placebo (an inactive substance that looks the same as, and is administered in the same way as, a drug in a clinical trial). Women on tamoxifen also had 49 percent fewer diagnoses of noninvasive breast tumors, such as ductal or lobular carcinoma in situ. Nine women died of breast cancer, three women in the tamoxifen group and six women in the placebo group (1).

In the BCPT, most of the side effects associated with tamoxifen were temporary. However, there were some long-term risks, including several serious health problems: endometrial cancer (cancer of the lining of the uterus), uterine sarcoma (cancer of the muscular wall of the uterus), pulmonary embolism (blood clot in the lung), deep vein thrombosis (blood clot in a large vein), and stroke. Because of these risks, women taking tamoxifen should be monitored by their doctors for any sign of serious side effects. All BCPT participants have been asked to undergo regular follow-up examinations.

BCPT participants who were randomized to the tamoxifen group and had not completed 5 years of tamoxifen therapy when the study ended were given the opportunity to continue on therapy. Postmenopausal women who had been taking the placebo were invited to participate in another trial, the Study of Tamoxifen and Raloxifene (STAR). (See the following section for a description of this trial.) Women in the BCPT placebo group also have the option of seeking tamoxifen from their doctor.

The Study of Tamoxifen and Raloxifene (STAR)

The NSABP is conducting the Study of Tamoxifen and Raloxifene, known as STAR. The study is funded primarily by the NCI. The 19,000 participants are postmenopausal women who are at least 35 years old and are at increased risk for developing breast cancer. The study will determine how raloxifene (Evista®), another SERM, compares with tamoxifen in reducing the incidence of breast cancer in women who are at an increased risk of developing the disease. As with tamoxifen, most of the known side effects of raloxifene are temporary. However, like tamoxifen, raloxifene increases the risk of pulmonary embolism and deep vein thrombosis. STAR is closed to new participants, and results are expected in the summer of 2006.

Capital Area SERM Study

The NCI is also conducting the Capital Area SERM Study to evaluate the safety of raloxifene in premenopausal women between the ages of 23 and 47 who are at increased risk for breast cancer. Thirty-seven women enrolled in this study. A complete report of the study’s findings will be published in 2005.

Other Breast Cancer Prevention Studies

Drugs called aromatase inhibitors, which have been approved by the U.S. Food and Drug Administration to treat hormone-sensitive breast cancer, are being studied in clinical trials for breast cancer prevention. These drugs interfere with the adrenal enzyme aromatase, which is responsible for estrogen production in postmenopausal women (2). The NCI is also studying prevention options for women at high risk of breast cancer that is not sensitive to hormones and can be more difficult to treat than hormone-sensitive breast cancer.

Scientists are also studying the basic biology of breast cancer to learn more about both non-hormone-sensitive and hormone-sensitive tumors. This research may lead to better ways of preventing all types of breast cancer.

NCI Priorities for Breast Cancer Prevention Research

Recognizing the impact of breast cancer on our society, in 1997 the NCI convened a Breast Cancer Progress Review Group (PRG) of experts and advocates to analyze the NCI’s breast cancer research activities and develop recommendations for the future. Based on its assessment of the status of breast cancer research, the review group recommended research priorities to accelerate progress in breast cancer prevention and treatment. In August 1998, the group published its report, Charting the Course: Priorities for Breast Cancer Research.

In October 2004, an internal NCI Breast Cancer Working Group assessed the advances made since the release of the PRG report. The Working Group released The NCI Breast Cancer Progress Report, which documents trends in NCI’s breast cancer research portfolio and the progress that has been made in meeting the priorities identified by the PRG. The report will help to guide the Institute as it moves forward in breast cancer research.

Estimating Breast Cancer Risk

Most breast cancer prevention trials involve women at increased risk of developing this disease. For example, it is clear that breast cancer occurs more often in women over age 60. Other factors associated with increased risk include a personal or family history of breast cancer and changes in certain genes such as BRCA1 and BRCA2. Scientists at the NCI and the NSABP have developed a computer program (on CD-ROM) called the Breast Cancer Risk Assessment Tool. This tool can help wom

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