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U.S. Preventive Services Task Force

Chemoprevention: Breast Cancer

Future Research

Many questions remain about chemoprevention of breast cancer (64). First, we need to learn more about the effects of the drugs. We need better information about the optimal dose, the duration of effect, the presence and magnitude of any reduction in breast cancer mortality, and the magnitude of the known and any unknown adverse or beneficial effects (65,66). Studies in women with breast cancer indicate that treatment with tamoxifen for longer than 5 years confers no additional benefit. Not known is what happens to the incidence of breast cancer once women stop the chemopreventive drug. Studies of adjuvant tamoxifen use for the treatment of breast cancer have found that the benefit lasts at least another 5 years and probably longer after the 5-year treatment period (67,68). Whether the same holds true for chemoprevention is not known.

Second, we need to learn how best to use tamoxifen and raloxifene. This includes finding better ways to select those women most likely to benefit and least likely to be harmed, and better ways to counsel them about the effects of chemoprevention (69,70). How many eligible women will choose to take tamoxifen or raloxifene for 5 years is uncertain.

Further clinical trials are needed to answer these and other questions. Many women in the BCPT placebo group began taking tamoxifen after the study results were made public. Thus, the BCPT is unlikely to provide further information on the many unanswered questions of chemoprevention. The International Breast Cancer Intervention Study (IBIS), based in the United Kingdom, Europe, and Australia, is an ongoing placebo-controlled study of breast cancer chemoprevention with tamoxifen (71). The National Cancer Institute has launched a study that will directly compare tamoxifen and raloxifene, the Study of Tamoxifen and Raloxifene (STAR) trial (NSABP P-2) (72). Results are anticipated by 2006. Another RCT, the Raloxifene Use for the Heart study (RUTH), will assess the effectiveness of raloxifene compared with placebo on both coronary heart disease and breast cancer (73). An important question is whether RUTH will corroborate the MORE finding of a beneficial CV effect of raloxifene.

Although the trade-off between benefits and harms for the present drugs, given current evidence, may be acceptable for a relatively small number of women, the findings from the studies of tamoxifen and raloxifene signal a new and promising direction for research in the control of breast cancer. We should pursue this direction energetically.

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We acknowledge the assistance of David Atkins, MD, MPH, Director; Dana Best, MD, MPH; and Eve Shapiro of the AHRQ Clinical Prevention Program. We are grateful to Carmen Lewis, MD, MPH and Margaret Wooddell, MA, for their assistance in reviewing the studies of tamoxifen and raloxifene cited in this paper. We are also grateful for the superb assistance of Audrina J. Bunton, BA and Lynn Whitener, MSLS, DrPH, of UNC and Sonya Sutton, BSPH and Loraine Monroe of the Research Triangle Institute. We would also like to acknowledge Bahjat Qaqish, MD, PhD for statistical assistance.

This study was developed by the RTI-UNC Evidence-based Practice Center under contract to the Agency for Healthcare Research and Quality (Contract No. 290-97-0011), Rockville, MD.

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Appendix. Methods

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Author Affiliations

[a] Linda S. Kinsinger: Cecil G. Sheps Center for Health Services Research; Department of Medicine; University of North Carolina at Chapel Hill, Chapel Hill, NC.
[b] Russell Harris: Cecil G. Sheps Center for Health Services Research; Department of Medicine; University of North Carolina at Chapel Hill, Chapel Hill, NC.
[c] Steven H. Woolf: Department of Family Practice; Virginia Commonwealth University, Fairfax, VA.
[d] Harold C. Sox: American College of Physicians-American Society of Internal Medicine, Philadelphia, PA.
[e] Kathleen N. Lohr: Research Triangle Institute, Research Triangle Park, NC.

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Source: U.S. Preventive Services Task Force. Chemoprevention of breast cancer: summary of the evidence. Ann Intern Med 2002;137:59-67.

Disclaimer: The authors of this article are responsible for its contents, including any clinical or treatment recommendations. No statement in this article should be construed as an official position of the U.S. Agency for Healthcare Research and Quality or the U.S. Department of Health and Human Services.

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Internet Citation

U.S. Preventive Services Task Force. Chemoprevention of Breast Cancer: Summary of the Evidence. Article originally in Annals of Internal Medicine 2002;137:59-67. http://www.uspreventiveservicestaskforce.org/3rduspstf/breastchemo/brstchemosum1.htm


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