Real-World Outcomes of First-Line Pertuzumab, Trastuzumab, and Taxane in HER2-Positive Metastatic Breast Cancer in Costa Rica: A Multicenter Retrospective Study

Background Dual HER2 blockade with pertuzumab, trastuzumab, and a taxane is the current standard first-line treatment for HER2-positive metastatic breast cancer (mBC), based on pivotal trials such as the CLEOPATRA. Since 2014, this regimen has been implemented in the Costa Rican public healthcare system. However, real-world data from Central America are lacking. Methods We conducted a retrospective, multicenter observational study of 148 patients with histologically confirmed HER2-positive mBC who were treated between August 2015 and August 2021 at five Costa Rican public hospitals. Primary endpoints were progression-free survival (PFS), overall survival (OS), and safety profile. Survival analysis was performed using Kaplan-Meier estimates. Results Median age was 58 years; 95% had ECOG 0-1; 54% were hormone receptor-positive. Visceral metastases were present in 37.8%, and 4.7% had brain metastases at diagnosis. Paclitaxel was the most used taxane (85%). Median duration of anti-HER2 therapy was 22.7 months. Median PFS was 19 months (95% CI: 15-25), and median OS was 73 months (95% CI: 38-74), with a median follow-up of 27.5 months. Most adverse events were grade 1-2, with peripheral sensory neuropathy (34%) and diarrhea (21%) being the most common. Grade 3 cardiotoxicity occurred in two patients. Subgroup analysis by hormone receptor status showed no statistically significant differences in PFS (HR-positive: 18.2 months (95% CI 14.1-22.3) vs. HR-negative: 20.1 months (95% CI 15.8-24.4); p = 0.42) or OS (HR-positive: 71 months (95% CI 36-106) vs. HR-negative: 74 months (95% CI 40-108); p = 0.38). Conclusion This first Central American real-world study demonstrates that first-line pertuzumab, trastuzumab, and taxane yields PFS, OS, and safety outcomes comparable to pivotal trials in HER2-positive mBC, despite including patients with prior trastuzumab exposure and brain metastases. These findings contribute to regional real-world evidence and underscore the need for neurological monitoring, given the high rate of central nervous system (CNS) progression. Cross-study comparisons remain descriptive due to population and design differences.