Abstract PS3-07-05: Clinical and Demographic Factors Associated with Discordant Oncotype (RS) and MammaPrint (MP) Scores in Patients with Hormone-Positive (HR+) Breast Cancer (BC). An Analysis of the National Cancer Database (NCDB)

Abstract Background: Patients with early-stage ER-positive breast cancer frequently undergo genomic assays like RS or MP to guide chemotherapy decisions. A discordance between these tests is observed, yet no prospective head-to-head trials exist to determine which assay is more predictive, posing challenges for clinicians. This study evaluates the clinical and pathological features of patients with discordant results and explores associated factors. Methods: We utilized the 2022 NCDB to include non-metastatic female breast cancer patients over the age of 18 who are hormone receptor-positive (HR+), HER2-negative, N0-1 with tumor stage T1-4, and who underwent both RS and MP. From this cohort, we compared the characteristics of patients with concordant results to those with discordant results. Within the discordant group, we identified two subgroups: High MP/Low RS, and High RS/Low MP. Tumor and patient characteristics were assessed using univariate analysis. Results: Out of 4,231,162 breast cancer patients, 2,014 patients underwent both MP and RS, of whom 35.25% (N=710) exhibited discordant results. Cases with discordant results were more likely to be high grade (grade 3: 21% vs. 17%; grade 2: 63% vs. 60%; p0.001), have ductal histology (85% vs. 79%, p0.001), and N0 disease (70% vs. 64%, p=0.005), and were more frequently Black (10% vs. 7.1%, p=0.011) compared to cases with concordant results. More patients with discordant results received chemotherapy compared to those with concordant results (41% vs. 24%; p0.001). Of the 710 discordant cases, 92.1% (n=654) had high MP/low RS, while 7.9% (n=56) had high RS/low MP. Compared to the high RS/low MP group, the high MP/low RS cases were more likely to be grade 3 (22% vs. 9.1%, p=0.016), have ductal histology (87% vs. 65%, p0.001), and include a higher proportion of premenopausal patients (34% vs. 16%, p=0.005). Chemotherapy utilization was equal at 41% in both discordant groups (p=0.96). Factors predicting chemotherapy utilization in the high MP/low RS group included median oncotype score (20 vs. 17), premenopausal status (49% vs. 23%), ductal histology (91% vs. 84%), T2 stage (41% vs. 26%), N1 stage (46% vs. 19%), and grade 3 disease (33% vs. 15%). Conclusion: This analysis revealed that the discordance rate between RS and MP is approximately 35%, with 92.1% of discordant cases exhibiting high MP and low RS. Chemotherapy utilization in both discordant groups is equal, indicating that providers are not making decisions based on one assay over the other. However, clinical factors such as premenopausal status, higher T stage, N1 disease, and grade 3 tumors influence chemotherapy decisions in discordant cases. Our study lacks survival data analyses due to a limited number of events. Citation Format: D. Desai, C. Widholm, P. Ashok Kumar, E. Hill, S. Sammons, A. Sivapiragasam. Clinical and Demographic Factors Associated with Discordant Oncotype (RS) and MammaPrint (MP) Scores in Patients with Hormone-Positive (HR+) Breast Cancer (BC). An Analysis of the National Cancer Database (NCDB) abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS3-07-05.