ERBB2 and breast cancer: However, in budget-constrained settings, assessing the cost-effectiveness of TDM-1 is essential to guide sustainable adoption.<h4>Objective</h4>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.<h4>Methods</h4>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).