title: Chemoprevention of breast cancer: a summary of the evidence for the U.S. Preventive Services Task Force.
abstract: OBJECTIVE
  Chemoprevention offers promise as a strategy for reducing morbidity and mortality from breast cancer in women. This review examined the evidence for the effectiveness of chemoprevention in women without a history of breast cancer.
  
  
  METHODS
  MEDLINE (1966 to December 2001).
  
  
  METHODS
  English-language, randomized, controlled trials (RCTs) of chemoprevention of breast cancer in women without a previous diagnosis of breast cancer were examined, and 4 relevant trials, 3 involving tamoxifen and 1 involving raloxifene, were selected. Trials that provided data on the harms of tamoxifen or raloxifene, studies of the costs of chemoprevention, and studies of risk assessment were also reviewed.
  
  
  METHODS
  Four reviewers independently abstracted data on key variables, including study population, sample size, randomization, treatment, and outcomes.
  
  
  RESULTS
  The largest of the RCTs of tamoxifen reported a 49% reduction in relative risk (0.51 [95% CI, 0.39 to 0.66]) for invasive cancer among women with an estimated 5-year breast cancer risk of at least 1.66%. The other tamoxifen trials did not observe a statistically significant benefit, but only a few women in each trial took tamoxifen during the entire study period. The raloxifene study of postmenopausal women with osteoporosis found a 76% reduction in relative risk (0.24 [CI, 0.13 to 0.44]) for invasive breast cancer. Tamoxifen and raloxifene were effective only against estrogen receptor-positive tumors. Both drugs increased risk for venous thromboembolic disease and hot flashes; tamoxifen increased risk for endometrial cancer and stroke.
  
  
  CONCLUSIONS
  Tamoxifen and raloxifene reduce the incidence of estrogen receptor-positive breast cancer in women. The relative risk reduction seems similar across all breast cancer risk groups. The absolute risk reduction varies by risk factors for breast cancer, however, and must be balanced against the potential harms to judge the appropriateness of treatment for individual women.
authors.affiliation: Cecil G. Sheps Center for Health Services Research, Program on Prevention, CB# 7508, Wing D, Room 383, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7508, USA.
authors.forename: Linda S
authors.initials: LS
authors.lastname: Kinsinger
authors.forename: Russell
authors.initials: R
authors.lastname: Harris
authors.forename: Steven H
authors.initials: SH
authors.lastname: Woolf
authors.forename: Harold C
authors.initials: HC
authors.lastname: Sox
authors.forename: Kathleen N
authors.initials: KN
authors.lastname: Lohr
mesh_terms: D016588:Anticarcinogenic Agents / Q000009:adverse effects / Q000627:therapeutic use; D018931:Antineoplastic Agents, Hormonal / Q000009:adverse effects / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000517:prevention & control*; D018890:Chemoprevention; D019317:Evidence-Based Medicine; D005260:Female; D006801:Humans; D011322:Primary Prevention; D020849:Raloxifene Hydrochloride / Q000009:adverse effects / Q000627:therapeutic use; D018570:Risk Assessment; D012307:Risk Factors; D020845:Selective Estrogen Receptor Modulators / Q000009:adverse effects / Q000627:therapeutic use; D013629:Tamoxifen / Q000009:adverse effects / Q000627:therapeutic use
chemical_list: D016588:Anticarcinogenic Agents; D018931:Antineoplastic Agents, Hormonal; D020845:Selective Estrogen Receptor Modulators; D013629:Tamoxifen; D020849:Raloxifene Hydrochloride