Abstract PO3-17-11: The Utility of Oncotype DX in Grade 1 Hormone Receptor-Positive Early Breast Cancer: Insights from a Multicentric Real-World Data Study

Abstract Background: The Oncotype Dx (ODX) genomic risk score (RS) has become an essential tool in clinical practice for guiding adjuvant chemotherapy decisions in early-stage hormone receptor-positive (HR+), HER2-negative breast cancer (BC). Since some of the genes evaluated in the genomic RS tests are proliferation-related, the use of the test is less clear in tumors with low proliferation, such as histologic grade 1 tumors or those with a low Ki67-index. In contrast to common understanding, however, ODX RS is determined more strongly by estrogen-related features and only weakly by proliferation markers. Methods: This multicentric real-world data (RWD) study aimed to evaluate the usefulness of (ODX) in patients with grade 1 (G1) HR+, HER2-negative BC. The study population consisted of patients treated between 2009 and 2020 across nine Brazilian cancer centers. Key endpoints included the prevalence of high genomic RS in the histologic grade 1 cohort, recurrence rates based on genomic risk, and invasive disease-free survival (IDFS). Results: A total of 651 patients with HR+, HER2-negative BC who underwent Oncotype Dx testing were evaluated. Among 651 patients evaluated, 128 had HG1 tumors, constituting the focus of this analysis. The majority of patients were aged over 50 years (59.4%), had breast carcinoma of non-special type (75.8%), and Ki67 index lower than 20% (77%). Tumor stage distribution revealed 28.1% T1b, 50% T1c, and 14% T2 cases. Additionally, 74.2% were classified as N0, 9.4% as N1mic, and 16.4% as N1. According to the binary categorization based on Adjuvant! algorithm, 92.2% of patients (n=118) had a low clinical risk. ODx analysis showed that 21.9% had a low RS, 74.2% had an intermediate RS, and only 3.1% had a high RS. Among the few patients with a high genomic RS, only one patient did not receive adjuvant chemotherapy. With a median follow-up of 38.3 months, three patients experienced recurrence, all of whom had an intermediate RS. Among these cases, two patients were younger than 50 years, had low clinical risk, and a genomic RS of 18-24; both had locoregional recurrences. The third patient, aged over 50 years, had high clinical risk, a RS of 12, and had a distant recurrence. The recurrence rates according to Ki67 index were 1.1% for patients with Ki67 index 20% and 7.1% for those with Ki67 index ≥ 20%. Notably, no recurrences were observed in the high genomic risk group. The estimated 5-year IDFS rate was 96.9% (95% CI 88.2% - 99.2%). Conclusion: In the context of G1 BC and low clinical risk, the utility and cost-effectiveness of ODX may be limited. These findings emphasize the importance of carefully assessing clinical risk when selecting patients for genomic RS tests, thereby optimizing resource utilization. Longer follow-up is planned for this RWD cohort. Citation Format: Renata Colombo Bonadio, Leandro Oliveira, Daniel Batista, Daniela Rosa, Artur Katz, Max Mano, Daniele Assad-Suzuki, Daniel Argolo, Solange Sanches, Rafael Kaliks, Débora Gagliato, Thais Megid, Daniel Musse, Tatiana Correa, Andrea Shimada, Romualdo Barroso-Sousa, Marcelle Cesca, Débora Gaudêncio, Larissa Moura, Julio Araujo, José Bines, Laura Testa. The Utility of Oncotype DX in Grade 1 Hormone Receptor-Positive Early Breast Cancer: Insights from a Multicentric Real-World Data Study 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 PO3-17-11.