Impact of Anti-HER2 Therapies on Potentially Avoidable Deaths from Stage II and III HER2-Positive Breast Cancer in the Brazilian Public Healthcare System

PURPOSE Limited access to contemporary anti-HER2 therapies in Brazil's public healthcare system (Sistema Único de Saúde -SUS) may contribute to avoidable mortality among women with HER2-positive early breast cancer. We estimated the number of potentially preventable deaths associated with incorporating adjuvant trastuzumab emtansine (T-DM1) and perioperative pertuzumab into SUS. METHODS We developed a static decision-tree microsimulation model with an 8-year time horizon. The study population was derived from nationwide real-world data from DATASUS, which captures all patients treated within SUS. Three treatment strategies were evaluated: (1) current SUS standard (perioperative trastuzumab only), (2) incorporation of adjuvant T-DM1 for patients with residual invasive disease after neoadjuvant therapy, and (3) a gold-standard regimen including perioperative pertuzumab and response-guided adjuvant T-DM1. Clinical inputs were obtained from the NeoSphere, APHINITY, and KATHERINE trials. Probabilistic sensitivity analysis with 100,000 simulations was performed to estimate mortality outcomes and 95% confidence intervals (CIs). RESULTS A total of 22,432 women with stage II–III HER2-positive breast cancer were identified. The projected mean number of deaths at 8 years was 3,606 (95% CI, 3,082–4,180) under the SUS standard, 2,672 (95% CI, 2,244–3,147) with adjuvant T-DM1, and 2,390 (95% CI, 2,034–2,790) with the gold-standard regimen. Incorporation of T-DM1 was associated with 934 fewer deaths (25.9% relative reduction), whereas full adoption of the gold-standard strategy was associated with 1,216 fewer deaths (33.7% relative reduction). CONCLUSION Expanding access to adjuvant T-DM1 and perioperative pertuzumab within SUS could meaningfully reduce mortality and narrow disparities in outcomes for Brazilian women with HER2-positive early breast cancer.