Disparities in mortality among HER2-positive breast cancer patients treated with trastuzumab in Chile (2015–2024): real-world evidence from 4,920 cases

BACKGROUND: HER2-positive breast cancer (BC) is an aggressive subtype that affects approximately 15-25% of patients. OBJECTIVE: This study aimed to identify sociodemographic factors associated with mortality among patients with HER2-positive BC treated with trastuzumab under the Ricarte Soto Law (RSL) in Chile between 2015 and 2024. METHODS: A cross-sectional observational design was used, based on a national database including 4,920 patients who accessed treatment through the RSL. Bivariate and multivariate logistic regression models were applied to evaluate factors associated with mortality. RESULTS: Older age, public healthcare system, and residence outside the Metropolitan Region were associated with higher mortality. These findings suggest that disparities in outcomes persist despite financial coverage of high-cost therapies, indicating the influence of structural and geographic factors on cancer care. CONCLUSIONS: This study provides real-world evidence to inform policies aimed at reducing inequities in access and outcomes among patients with breast cancer in Chile.