Abstract P2-03-02: Prospective assessment of the decision-making impact of the Breast Cancer Index in the BCI Registry Study

Abstract Background: The Breast Cancer Index (BCI) is a validated gene expression assay that provides a quantitative individualized risk of late recurrence and predicts the likelihood of benefit from extended endocrine therapy (EET) in HR+ early-stage breast cancer. The objective of this analysis was to assess the impact of BCI on clinical decision-making regarding EET in the BCI Registry Study. Methods: The BCI Registry Study is an ongoing, prospective, large-scale study to investigate the long-term clinical outcome, decision impact, and medication adherence in HR+ early-stage breast cancer patients receiving BCI testing as part of routine clinical care. Per protocol, physicians and patients completed pre- and post-BCI test questionnaires to assess the following: physician decision-making regarding EET; physician confidence with decision-making; patient preferences for EET; patient concerns about the cost, side effects, drug safety and benefit of EET; and patient satisfaction regarding treatment recommendation. Pre- and post-BCI responses were compared using McNemar’s test and Wilcoxon signed rank test. Results: Pre- and post-BCI test physician and patient questionnaires were completed for 843 and 823 patients, respectively. For the patients included in this analysis, mean age at enrollment was 65y and 88.4% of patients were postmenopausal. 74.7% of tumors were T1, 53.4% were G2, 75.3% N0, and 13.8% HER2-positive. Following BCI testing, physicians changed treatment recommendations for EET in 40.1% (338/843) of patients (p< 0.0001). In cases in which physicians recommended EET prior to BCI testing, 44.7% (214/479) changed their recommendation not to extend endocrine therapy. Of these cases, 98.1% (210/214) were BCI Prognostic low risk and/or BCI (H/I) Predictive low likelihood of benefit from EET. In cases in which physicians did not recommend EET prior to BCI testing, 34.6% (124/358) changed their recommendation in favor of EET. In such cases, 87.1% (108/124) of cases were BCI Prognostic high risk and/or BCI (H/I) Predictive high likelihood of benefit from EET. Further, following BCI testing, 38.8% (327/843) of physicians felt more confident in their recommendation (p< 0.0001). The percentage of physicians having high confidence levels (confident or strongly confident) increased from 58.1% (490/843) before BCI testing to 80.5% (679/843) after BCI testing. The percentage of physicians having low confidence levels (not at all confident, not confident, or ambivalent) decreased from 39.1% (330/843) before BCI testing to 18.7% (158/843) after BCI testing. In addition, 40.5% (341/843) of patients felt more comfortable with their EET decision (p< 0.0001) following BCI testing. Notably, changes in patient preferences for EET correlated with BCI test results. In BCI (H/I)-Low patients, 46.9% (241/514) showed a decreased preference for EET (p< 0.0001) while in BCI (H/I)-High patients, 28.2% (87/309) showed an increased preference for EET (p< 0.0001). Compared with baseline, after BCI testing, significantly more patients were less concerned about cost (20.9%, p< 0.0001), drug safety (25.4%, p=0.0014), and the benefits of EET (29.3%, p=0.0002). No significant change in concern regarding side-effects was observed (p=0.1486). Conclusions: This first analysis in a large patient cohort of the BCI Registry confirms previous findings on the significant clinical decision-making impact of BCI for extending adjuvant endocrine therapy. Incorporating BCI into clinical practice resulted in changes in physician recommendations for EET in over 40% of cases, while at the same time increasing physician confidence in their recommendations. Knowledge of the BCI result also improved patient satisfaction and reduced patient concerns regarding cost, drug safety and benefit of EET. Citation Format: Tara B. Sanft, Jenna Wong, Brandon O’Neal, Natalia Siuliukina, Rachel C. Jankowitz, Mark Pegram, Jenny Fox, Yi Zhang, Kai Treuner, Joyce O’Shaughnessy. Prospective assessment of the decision-making impact of the Breast Cancer Index in the BCI Registry Study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-03-02.