Prospective decision impact study of the Breast Cancer Index: Results from the BCI Registry study.

531 Background: The Breast Cancer Index (BCI) is a validated gene expression assay that provides an individualized risk of late distant 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 influence of BCI on clinical decision-making regarding EET. Methods: The BCI Registry study is a prospective, multi-institutional study investigating the long-term clinical outcome, decision impact, and quality of life in HR+ breast cancer patients receiving BCI testing as part of routine clinical care. Physicians and patients completed pre- and post-BCI test questionnaires to assess physician decision-making; physician confidence; and patient preferences and concerns for EET. Pre- and post-BCI responses were compared using McNemar’s test and the Wilcoxon signed rank test. The BCI Registry Study is registered on ClinicalTrials.gov under NCT04875351. Results: In the current analysis,pre- and post-BCI testing questionnaires were completed for 2850 physicians and 2832 patients. 88.6% of patients were postmenopausal, 76.5% N0, 73.0% T1, 53.5% G2, and 13.0% HER2-positive. Following BCI testing, physicians changed treatment recommendations for EET in 41.2% (1175/2850) of patients (p<0.001). In cases where physicians recommended EET prior to BCI testing, 49.8% (775/1555) changed their recommendation to not treat with EET, while 31.2% (400/1280) of those who did not recommend EET prior to BCI testing changed their recommendation in favor of EET. Following BCI testing, 43.9% (1250/2850) of physicians felt more confident in their recommendation (p<0.001) and 43.2% (1223/2832) of patients felt more comfortable with their EET decision (p<0.001). The percentage of physicians having high confidence levels (confident or strongly confident) increased from 63.6% (N=1813) pre-BCI testing to 88.2% (N=2515) post-BCI testing. The percentage of physicians having low confidence levels (not at all confident, not confident, or ambivalent) decreased from 33.1% (N=943) pre-BCI testing to 11.0%(N=313) post-BCI testing. In BCI (H/I)-Low patients, 48.9% (868/1776) showed a decreased preference for EET (p<0.001). In BCI (H/I)-High patients, 34.6% (365/1056) showed an increased EET preference (p<0.001). After BCI testing, significantly more patients were less concerned about cost (23.9%, p<0.001), drug safety (25.7%, p<0.001), and EET benefit (30.9%, p<0.001). No significant change in concern regarding side-effects was observed (p=0.58). Conclusions: Incorporating BCI into clinical practice resulted in significant changes in physician recommendations for EET, while at the same time increasing physician confidence. Knowledge of the BCI result improved patient preference, satisfaction and reduced patient concerns regarding cost, drug safety and benefit of EET.