Adjuvant therapy for HR+/HER2-early-stage breast cancer (EBC): Changes in practice patterns among community oncologists in Brazil

e18820 Background: The management of HR+/HER2– early breast cancer (EBC) has changed significantly, with more patients are being classified as low-risk and spared adjuvant chemotherapy (CT) and de-escalating endocrine therapy (ET); on the other hand, other patient groups have experienced treatment escalation, such as high-risk premenopausal women. This study aims to assess practice patterns and real-world data for patients with HR+/HER2- EBC treated in Brazil's largest network of community oncology practices. Methods: Retrospective real-world study from the Oncoclínicas with longitudinal EHR data merged in a platform where structured variables were integrated with unstructured elements from physician notes using technology-based abstraction and expert human curators that follow mCODE standards and predefined ontology. Index data was EBC diagnosis date, and we restricted the study to patients diagnosed between Jan 2017 and Jun 2022, with comparative analysis of adjuvant CT/ET practice trends in 2017-2019 versus 2020-2022. Results: From over 30k patients with breast cancer in Oncoclínicas Database, 19k had HR+/HER2– EBC, 12k were treated in high-volume clinics, and 2,988 were selected for the study due to data accessibility in the pre-specific observation period. Stage distribution: I in 45%, II in 37%, and III in 18%. Pre-menopausal status at diagnosis: 22%. Less than 5% of the study population had access to breast cancer prognostic risk scores. The disease-free survival rate in the entire cohort was 87% (CI95% 86-89) at 2 years and 74% (CI95% 70-78) at 5 years. Overall, we observed a decrease in adjuvant CT use from 51% during 2017-2019 to 41% during 2020-2022. In pre- menopausal patients, CT use reduced from 68% in stage I during 2017-2019 to 41% during 2020-2022; for stage II or III, the reduction was less noticeable (83% in 2017-2019 to 75% in 2020-2022). In post-menopausal patients, CT use reduced from 36% in stage I during 2017-2019 to 18% during 2020-2022; while it remained stable in stage II or III (55% in 2017-2019 versus 52% in 2020-2022). Concerning ET, there were no evident changes in treatment practice. In pre-menopausal, tamoxifen alone was the first option in 90% with stage I and in 64% with stage II or III, with the stability over the years. In post-menopausal, aromatase inhibitors were the first option in 61% with stage I, 70% with stage II and 77% with stage III, with the stability over the years. Conclusions: We perceived a reduction in chemotherapy use in HR+/HER2– stage I breast cancer over time. Reasons for treatment selection must be investigated further, including other prognostic factors, but might be related to greater physician confidence in avoiding CT and access to genomic signatures. There were no significant changes in patterns of adjuvant ET, with most pre- and postmenopausal patients receiving tamoxifen alone and an aromatase inhibitor respectively.