Clinical utilization of Breast Cancer Index (BCI) for late recurrence risk assessment and prediction of extended endocrine therapy (EET) benefit in early stage HR+ breast cancer.

Abstract

551 Background: Randomized trials demonstrated a modest (3-5%) absolute benefit from EET in patients (pts) with early stage HR+ breast cancer (BC), but also a risk of toxicities. BCI is a validated gene expression-based assay that provides 2 results: BCI Prognostic, based on the algorithmic combination of HoxB13/IL17BR (H/I ratio) and a set of proliferation-based genes, reports individualized risk of late distant recurrence (DR); BCI Predictive, based on H/I alone, reports a prediction of high vs low likelihood of benefit from EET. The objective of this study was to assess clinical and pathologic patient characteristics, prognostic and predictive assay results, and physician testing patterns in >14,000 clinical cases. Methods: The BCI Clinical Database for Correlative Studies is a de-identified database developed under an IRB approved protocol that contains >50 clinicopathologic and molecular variables from cases submitted for BCI in clinical practice. Clinicopathologic variables were abstracted from pathology reports, and were available for a subset of cases. Results: Across all pts (N=14,463), median age was 58.2y (range: 23-92y; 73.9% ≥50y). The majority were Stage I (47.3% IA, 3.5% IB, 29.1% IIA, 14.1% IIB, 6% III). Cases were 29%, 51%, and 20% Grade 1, 2, and 3, respectively. Most pts were ER+/PR+ (87.7%) or ER+/PR- (11.3%); 11.3% were HER2+. The majority of cases (55.7%) were ordered 4-6y postdiagnosis, with 23.1% >6y, 14.4% between 1-4y, and 6.8% <1y postdiagnosis. In LN- pts (n=3395), BCI Prognostic identified 50.6% as low risk for late DR vs 49.4% as high risk, while BCI Predictive (H/I) classified 41.0% as high vs 59.0% as low likelihood of benefit. In LN+ pts tested with the BCIN+ Prognostic algorithm (BCI + size/grade, n=818), 77.3% were classified as high risk vs 22.7% as low risk, while BCI Predictive (H/I) classified 44.6% and 55.4% as high vs low likelihood of benefit. Conclusions: Findings from this large cohort characterize utilization of BCI in clinical practice for pts with early-stage, HR+ BC. BCI stratification of pts with high risk and high likelihood of benefit from EET may facilitate selection of pts for prolonged regimens.