BACKGROUND: Several randomized clinical trials have tested the hypothesis that @entity440 is effective in preventing @entity0 . The largest such trial, the National Surgical Adjuvant Breast and Bowel Project's @entity0 Prevention Trial (BCPT), reported a 49% reduction in risk of @entity0 for the @entity440 group. However, it is unclear whether the effect of @entity440 in this trial was mainly due to prevention of newly forming @entity5 or to treatment of @entity66 . METHODS: We used various @entity5 growth models (i.e., exponential and Gompertzian [growth limited by @entity5 size]) and a computer simulation to approximate the percentage of detected @entity5 that were initiated after study entry. Maximum likelihood techniques were then used to estimate separately the efficacy of @entity440 in treating @entity66 and in preventing the formation and growth of new @entity5 . RESULTS: Under the assumptions of most of the growth models, the trial was sufficiently long for substantial numbers of new @entity5 to form, grow, and be detected during the trial. With the Gompertzian model and all available incidence data from the BCPT, it was estimated that 60% (95% confidence interval [CI] = 40%-80%) fewer new @entity5 were detected in the @entity440 group than in the placebo group. Likewise, 35% (95% CI = 6%-63%) fewer @entity5 were detected in the @entity440 group. With this model, the estimated incidence rate of @entity0 among @entity1 in the placebo group of the BCPT was 7.7 (95% CI = 6.6-8.9) per 1000 @entity1 per year. Similar results were obtained with three exponential @entity5 growth models. CONCLUSIONS: These results support the concept that @entity440 reduced @entity5 incidence in the BCPT through both treatment of @entity66 and prevention of new @entity5 formation and growth. However, data from prevention trials may never be sufficient to completely distinguish prevention of new @entity5 formation from treatment of @entity66 .

Estimation of XXXX 's efficacy for preventing the formation and growth of @entity0 .

@entity1 :: ('9606', 'Species') :: ['women'] @entity0 :: ('MESH:D001943', 'Disease') :: ['Breast Cancer', 'breast cancer', 'invasive breast cancer'] @entity440 :: ('MESH:D013629', 'Chemical') :: ['tamoxifen'] @entity66 :: ('MESH:D004194', 'Disease') :: ['occult disease'] @entity5 :: ('MESH:D009369', 'Disease') :: ['tumor', 'cancer', 'occult tumors', 'tumors']
@entity440 :: (MESH:D013629,Chemical) :: ['tamoxifen']
