e12519 Background: The 21 gene assay Oncotype Dx Breast Recurrence Score (RS) is currently the standard of care to determine if adjuvant chemotherapy is needed in early stage node negative, hormone receptor positive, HER-2 negative breast cancer. In current American society of clinical oncology (ASCO) guidelines there is little or no benefit of adjuvant chemotherapy in patients older than 50 years whose tumors have Oncotype DX RS <26, and for patients 50 years or less whose tumors have Oncotype DX RS <16. We sought to evaluate the percentage of estrogen receptor (ER) expression as a surrogate measure of determining adjuvant chemotherapy by examining the relationship between ER expression and RS. Methods: We identified 301 patients from years 2015 to 2019 from our cancer registry with early stage hormone receptor positive breast cancer and had oncotype DX testing performed. We divided patients into three groups: Group 1 (ERG1) with ER <10%; Group 2 (ERG2) with ER 10-49%; and Group 3 (ERG3) with ER equal or >50%. We also collected information on tumor size (cm), tumor grade, Nottingham score, and ki-67 percentage. A sub-group analysis was performed for patients < 50 years age (n=30). We compared all continuous variables across ER groups using the Kruskal-Wallis rank test and individual between group comparisons using the Wilcoxon rank sum test. All statistical tests performed utilized a two-tailed p value of <0.05 with the Bonferroni correction for multiple comparisons. Results: Among 301 patients with early stage hormone receptor positive breast cancer, 89.1% were ductal, 7.9% lobular, and 2.9% mixed histology. Median age was 68, 58 and 66 for ERG1, ERG2, and ERG3, respectively (p = 0.41). Median RS was 36 (ERG1), 23 (ERG2), and 16 (ERG3) (p = 0.78 for ERG1 vs. ERG2; p = 0.01 for ERG1 vs. ERG3). As expected, tumor grade, tumor size, and Nottingham score decreased significantly from ERG1 to ERG3. For patients <50 years, median age was 44, 46 and 45 for ERG1, ERG2, and ERG3, respectively (p = 0.75). Median RS was 10 (ERG1), 24 (ERG2) and 18 (ERG3) (p = 0.04 for ERG1 vs. ERG2; p = 0.17 for ERG1 vs. ERG3). Conclusions: We found a significant association between estrogen receptor levels and Oncotype Dx recurrence score (RS) in patients with early stage hormone receptor positive breast cancer patients. Further studies are needed to determine the predictive ability of hormone receptor levels on the outcomes of patients treated for early stage hormone receptor positive breast cancer.
PCN216 ADJUVANT CHEMOTHERAPY GUIDED BY A 21-GENE EXPRESSION ASSAY IN HORMONE-RECEPTOR POSITIVE EARLY-STAGE BREAST CANCER: USE OF SIMULATION MODELING TO EXTEND AND TRANSLATE CLINICAL TRIAL RESULTS INTO PRACTICE
