Abstract PO3-02-04: Comparison of OncotypeDX Recurrence Scores (RS) and MammaPrint (MP) scores, and chemotherapy indications in early-stage Estrogen Receptor positive/HER2 negative (ER-/HER2-) breast cancer

Abstract Background: Both RS and MP are endorsed by ASCO and NCCN practice guidelines to estimate prognosis of early-stage ER+/HER2- breast cancers and results guide adjuvant chemotherapy treatment recommendations. Earlier studies reported around 30% discordance in risk assignments by different genomic assays, but these comparisons were complicated by the 3-way (low, intermediate, high) versus 2-way (low, high) risk assignment by RS and MP respectively. More recently, RS thresholds were re-evaluated in the context of the TAILORx and RxPONDER randomized clinical trials and RS 25 is now considered indication for adjuvant chemotherapy. MP results are now also reported as continuous scores similar to RS, and MP high risk patients can be subdivided into MP1 (high) and MP2 (ultra-high) risk groups. The goal of this analysis was to assess correlation between RS and MP scores as continuous variables and examine concordance in chemotherapy eligibility and risk category assignments. Methods: 168 patients treated at the West Cancer Center and Research Institute had patients with both MP and RS results available for the same patient generated by Agendia as a research activity and Exact Sciences in the context of routine care. Molecular class was assigned by the MammaPrint Blueprint assay. Results and clinical information were retrieved from the medical records. Median age was 64 years (range 25-92), 77% were postmenopausal, 59% White, 37% Black and 4% other. 78% had histologic grade 1 or 2 cancers, 53%, 38%, and 8% were stage I, II, and III, respectively. 84% were invasive ductal carcinoma, 13% invasive lobular carcinoma, the rest mixed or other rare histologies. Patients were considered high-risk and chemotherapy eligible if the RS was 25 or the MP score was 0 (i.e. any negative value), MP high-risk patients were further categorized into MP1 (MP score between 0 to -0.5699) and MP2 (MPs score -0.57 or less). Correlation between scores were assessed using Pearson correlation. Results: There was statistically significant correlation between RS and MP scores with a Pearson correlation coefficient of -0.61, (p 0.0001). 51 (30%) cancers were MP low-risk (Luminal A), and 122 (73%) were RS low risk (RS≤25). Among the MP low-risk cancers, 47 (92%) had concordant low risk assignment by RS. Based on RS, 46 (27%) patients were high-risk chemotherapy eligible and 42 of these (91%) were concordantly classified as MP high-risk. MP high-risk cancers included 115 Luminal B and 1 Basal-like cancers, and 64% of these (n=74) had low-risk status by RS. When the MP high category was subdivided into MP 1 (n=105) and MP2 (n=11) subgroups, (35/105) 33% and (7/11) 64% of cases were RS 25, respectively. Black patients had a statistically higher mean index MP score of -0.191 compared to -0.082 for White patients (p=0.02). No statistical difference was noted by race for RS. Conclusions: There was strong concordance (92%) between low-risk MP and low-risk RS. Similar concordance was not identified when comparing chemotherapy eligible high-risk MP (MP1 and MP2) to high-risk ( 25) recurrence scores. Only 36% of chemotherapy eligible MP patients (MP1 and MP2) would be chemotherapy eligible by RS. Higher concordance (58%) for chemotherapy eligibility was seen when limited to the ultra-high (MP2) scores. By contrast most (92%) of chemotherapy eligible patients by RS (25) were considered high risk by MP (MP1 or MP2). Table1. RS and MP risk categories Citation Format: Rishika Singh, William Barlow, Nupur Singh, James Elliott, Richard Fine, Michael Berry, Erin Cobain, Lajos Pusztai, Gregory Vidal. Comparison of OncotypeDX Recurrence Scores (RS) and MammaPrint (MP) scores, and chemotherapy indications in early-stage Estrogen Receptor positive/HER2 negative (ER-/HER2-) breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-02-04.