Abstract P3-15-01: The effect of participation in RCT on outcomes in patients with early breast cancer compared to the general breast cancer population
Authors: MB Brennan, D Wiley, D Wang, X Wang, P Fasching
Journal: Cancer Research (2018)

Abstract Background: Breast cancer trial enrollment, while slightly higher than some other histologies, still remains low, at less than 4%. Research suggests lack of clinical trial participation is due to poor patient and clinician commitment and interest. Increasing incentive for trial participation may enhance engagement of patients and healthcare providers leading to increased patient enrollment. One incentive would be to understand benefits of trial participation with regards to better survival and outcomes. The purpose of this study is to determine differences in survival, overall and breast cancer specific, and surgical management, for women who participate in early breast cancer randomized clinical trials (RCT) compared to the general breast cancer population who received similar standard therapy outside of a RCT. Methods: Patients included in this retrospective analysis were from one of three (3) international, randomize, adjuvant breast cancer trials (RCT-participants) and women with breast cancer from the general U.S. population, from Surveillance Epidemiology and End Results Program (SEER-13), the controls. Women diagnosed between 1997-2004 with invasive breast cancer, tumor (T) size 1-3, lymph node (LN) positive (LN1/2), hormone receptor positive or negative, HER2 positive or negative, treated with surgery, adjuvant radiation, and chemotherapy were included in the analysis. In this study, propensity score analysis (PSA) was done to provide weight to each data point for each variable in order to more closely represent similar populations. PSA, considered superior to a standard Cox multivariate analysis as it attempts to reduce the bias due to confounding or correlated predictive variables. Subsequently, the propensity score was applied to a Cox proportional hazards model to determine hazard ratios (HR), with a Wald 95% confidence interval (CI), of trial participation on survival. Similarly, PSA was done for surgical outcomes. A multivariate logistic regression was performed to calculate the odds ratios, with a Wald 95% CI, to determine if RCT participation compared to the SEER-13 control had an impact on surgical outcomes, mastectomy versus breast conserving surgery (BCS). Results: The total sample size was 9255 patients, 1795 RCT-participants and 7460 SEER-13 controls. After controlling for all other significant predictors of survival, RCT participation significantly reduced risk of breast cancer related death at 5-years by more than 25% and 18% at 10 years [HR: 0.75 (95% CI: 0.64-0.87); p=0.00020; and HR: 0.83 (95% CI: 0.74-0.93); p=0.00165, respectively]. Additionally, we demonstrated a significant reduction in risk of all-cause mortality for RCT-participants, at both 5-years and 10-years [HR: 0.83 (95% CI: 0.72--0.95); p=0.009; and HR: 0.79 (95% CI: 0.71-0.87); p&amp;lt;0.00001, respectively]. Additionally, RCT-participants were significantly less likely to undergo invasive surgical management (mastectomy) compared to SEER-13 controls [OR: 0.78 (95% CI: 0.66-0.92;) p=0.03]. Conclusion: RCT-participants have a reduced risk of death at 5 years and 10 years compared to the general breast cancer population. Additionally, RCT-participants are less likely to undergo mastectomy than the SEER-13 controls. Citation Format: Brennan MB, Wiley D, Wang D, Wang X, Fasching P. The effect of participation in RCT on outcomes in patients with early breast cancer compared to the general breast cancer population [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-15-01.