Abstract
BACKGROUND: Patients with HER2-positive (HER2+) breast cancer (BC) who have residual invasive disease after neoadjuvant therapy remain at a significantly increased risk of recurrence. Updated results from the KATHERINE trial demonstrated the clinical benefit of trastuzumab-emtansine (T-DM1), showing a significant improvement in event-free survival. However, in budget-constrained settings, assessing the cost-effectiveness of TDM-1 is essential to guide sustainable adoption. OBJECTIVE: To evaluate the cost-effectiveness analysis of adjuvant T-DM1 compared with trastuzumab in HER2+ early BC patients and residual disease, following neoadjuvant treatment, from the Colombian Health System perspective. METHODS: We conducted a Markov model with a lifetime horizon to evaluate the cost-effectiveness of T-DM1 using the updated results of the KATHERINE trial (8.4-year follow-up). The model comprises 6 health states: patients with residual invasive disease on adjuvant treatment, non-metastatic recurrence, remission after non-metastatic recurrence, metastatic disease (first-line [1LmBC] and subsequent lines [2LmBC]), and death. Direct medical costs were included. The primary outcome was quality-adjusted life-years, with both costs and effects discounted annually at a 5% rate. Model assumptions were based on current guidelines and validated by local experts. Sensitivity and scenario analysis were performed to confirm the reliability of the results. Prices are shown in 2024 US dollars (4071.35 Colombian pesos = US $1). RESULTS: Under a willingness-to-pay threshold of 86% of the 2024 gross domestic product per capita (US 6831), T - DM1wasdominantovertrastuzumab.Costsavingsweremainlydrivenbyareductioninrecurrences( > 50 -30 510) and 2LmBC (US $-6317). The probabilistic sensitivity analysis confirmed T-DM1 dominance in 81.2% of the 1000 Monte Carlo simulations, demonstrating consistency across settings. CONCLUSION: T-DM1 is a cost-effective and dominant strategy for the adjuvant treatment of residual invasive HER2+ early BC in Colombia, driven by cost savings from reduced high-cost recurrences. These findings support the adoption of T-DM1 to improve outcomes while ensuring efficient use of healthcare resources.