A Comparison of Genomic Assays in Determining Risk of Late Recurrence and Benefit of Extended Endocrine Therapy (EET).

e12045 Background: Breast cancer patients who are ER positive, lymph node negative have the best overall prognosis. However 50% of recurrences occur after 5 years. The Breast Cancer Index (BCI) is a gene expression-based biomarker that provides an individual risk of distant recurrence and benefit of EET based on a continuous risk model. (1) The BCI may help with clinical decisions regarding EET since prolonged therapy may have an increase in side effects including uterine cancer, DVT, myalgias and bone loss. The OncotypeDX is a 21 gene assay that predicts recurrence with a recurrence score. A recent study by Wolmark et al. evaluated the use of quantitative Estrogen Receptor Index (ESRI) combined with RS and found that RS was prognostic in patients with higher quantitative ESRI, suggesting EET be used for patients with intermediate and high RS with ESR1 expression > 9.1. (2) Methods: 20 patients, ER positive, node negative who had the BCI and ONC-DX performed were evaluated in this retrospective IRB approved review. Results: Using ESRI alone 85% of patients would be recommended to continue an additional 5 years of EET. Using BCI this number was reduced to 35%. Conclusions: Comparing both the risk of recurrence and benefit of ETT, ESRI and BCI were concordant only 37.5% of the time. The cost of extended adjuvant therapy with Anastrazole ($190/mos x 60 mos = $11,400) or Tamoxifen ($50/mos x 60 mos = $ 3,000) would have resulted in a cost savings of $79,800 (Anastrazole) or $21,000 (Tamoxifen) for this small group of patients. Utilization of the BCI (cost $ 3416.00) may be a cost effective and accurate genomic approach in determining the use of EET and avoiding concomitant side effects.