Background: Randomized trials have demonstrated significant but modest (3-5%) benefit from extended (10y) endocrine therapy (EET) vs 5y in pts with early stage ER+ breast cancer. Clinical practice guidelines have speculated on the risk vs benefit of EET in pts with a low clinicopathologic risk profile. Breast Cancer Index (BCI) is a gene expression-based test that that is prognostic for risk of late (> 5y) recurrence and predictive of EET benefit. This study examined the clinical utility and utilization of BCI in clinical practice, and its ability to identify pts likely to benefit from EET in an otherwise low risk population. Methods: Consecutive cases (N = 853) from LN- pts submitted for BCI prognostic and BCI predictive [HoxB13/IL17BR (H/I) ratio] analyses were investigated. Patient characteristics, clinician testing patterns, and clinical results were analyzed descriptively. Results: Patient characteristics are shown in the top table. BCI identified 54% and 46% as having low and high risk of late recurrence, respectively. Predictive testing identified 42% of pts with a high likelihood vs. 58% with a low likelihood of benefit from EET. The bottom table shows the integrated prognostic and predictive results. In the subset of pts with a low clinicopathologic risk profile (LN-, T1, Grade 1-2, HER2-neg; n = 321), BCI identified 23% of pts with both a high risk of late recurrence (mean, 7.1% DRR) and likely to benefit from EET. Physicians utilized BCI across a range of intervals from time of diagnosis: 11% < 2y; 14% ≥ 2 to < 4y; 57% ≥ 4 to < 6y; and 18% ≥ 6y. Conclusions: Data from this large retrospective analysis further define BCI clinical utility in selection of which early-stage, ER+ pts are at risk of late recurrence and likely to benefit from EET vs those that may be adequately treated with 5y of endocrine therapy.