Abstract PS4-12-03: Access-her: assessing consequences of standard-of-care gaps in her2-positive breast cancer in the brazilian healthcare system

Abstract Background: Dual HER2 blockade with pertuzumab and trastuzumab, followed by adjuvant trastuzumab-emtansine (T-DM1) for residual disease, has been the undisputed global standard of care for high-risk HER2-positive early breast cancer (EBC). These regimens have demonstrated significant improvements in pathological complete response and overall survival in pivotal trials. However, neither pertuzumab nor T-DM1 is currently available in the Brazilian Unified Health System (SUS), leading to a critical gap between internationally recommended treatment and what is offered to patients in the public sector. This disparity may lead to worse oncological outcomes, including increased mortality. The present study aimed to estimate the number of preventable deaths associated with the lack of access to these therapies in non-PCR patients in Brazilian non-PCR patients in Brazil. Methods: We conducted a retrospective, scenario-based modeling study using real-world data from DATASUS, the national public health database in Brazil. The study population included women aged 18 years or older who initiated treatment for stage II or III HER2-positive early breast cancer (EBC) within the SUS in 2023. Three treatment scenarios for patients with residual disease after neoadjuvant therapy were modeled. The first scenario, representing current practice in SUS, consisted of trastuzumab neoadjuvant followed by adjuvant trastuzumab alone (SUS Standard of Care). The second scenario (Scenario 2) incorporated adjuvant trastuzumab emtansine (T-DM1) for patients with residual disease. The third scenario (Scenario 3) simulated neoadjuvant dual HER2 blockade with pertuzumab and trastuzumab, followed by adjuvant T-DM1 in non-pCR cases. Model parameters, including total pathologic complete response (tpCR) rates and 7-year overall survival (OS), were derived from the pivotal NeoSphere and KATHERINE trials, respectively. Estimated 7-year mortality was calculated for each scenario, and preventable deaths were defined as the difference in projected mortality between the SUS Standard and the two alternative scenarios. Results: A total of 6,061 women with stage II-III HER2-positive early breast cancer initiated treatment within the SUS in 2023, including 1,381 patients with stage II disease and 4,680 with stage III. Based on the scenario model, an estimated 744 deaths over seven years would occur under the SUS Standard of Care Scenario. In contrast, Scenario 2 projected 520 deaths, and Scenario 3 projected 402 deaths. These represent relative reductions in 7-year mortality of approximately 30% and 46%, respectively, when compared to the SUS Standard of Care. When stratified by clinical stage, Scenario 2 was estimated to prevent 51 deaths in stage II and 173 deaths in stage III. The Scenario 3, incorporating neoadjuvant pertuzumab and adjuvant T-DM1, was estimated to prevent 78 deaths in stage II and 264 in stage III. In total, adoption of the Scenario 3 could result in more than 342 preventable deaths per annual cohort. Conclusion: This analysis demonstrates that the absence of pertuzumab and T-DM1 from the Brazilian public health system may lead to over 342 preventable deaths annually among patients with high-risk HER2-positive early breast cancer. The estimated reductions in long-term mortality with access to standard-of-care regimens underscore the urgent need to align national treatment protocols with internationally accepted guidelines. Incorporating these therapies into the SUS is essential to address systemic inequities in breast cancer care and to improve survival outcomes for patients treated in the public sector in Brazil. Citation Format: A. Mattar, F. Cavalcante, C. La-Scala, E. Pavanel, G. Tiguman, I. Silveira, N. Correa-Netto, V. Cano. Access-her: assessing consequences of standard-of-care gaps in her2-positive breast cancer in the brazilian healthcare system 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 PS4-12-03.