Genomic Stratification With Bci Of Er Plus Early Breast Cancer Patients With Limited Long-Term Risk Of Breast Cancer Death.

516Background: An increasing body of evidence from extended endocrine therapy trials underscores the unmet need to manage risk-benefit at the individual patient (pt) level. Breast Cancer Index (BCI) is a multigene assay that identified women with a 4.8%-6.6% low risk of cumulative recurrence (0-10y) and a low risk of late recurrence of 2.5%-3.5% in validation studies. In this post-hoc analysis, an optimized assay threshold to identify patients with favorable long-term breast cancer–specific survival was developed and characterized. Methods: An adjusted BCI cut point for indolent disease was trained using a cohort of node-negative, post-menopausal women with HR+ breast cancer from the Stockholm trial treated with surgery alone (UNT, n = 283). Initial performance of the optimized model was evaluated in tamoxifen-treated HR+ patients (TAM, n = 317). Breast cancer–specific survival (BCSS) was the primary analysis using Kaplan-Meier estimates over 0-20y and 5-20y. Subsets based on tumor size and tumor grade we...