Objective: To estimate, from the health system perspective, the cost-effectiveness of the use of trastuzumab emtasine (T-DM1), compared with trastuzumab, for the adjuvant treatment of adult patients with HER2+ early breast cancer who have residual invasive disease after neoadjuvant therapy in Colombia.

Methods: We developed a Markov model with six health states (invasive disease-free survival, non-metastatic recurrence, remission, metastatic setting that include first and further lines of treatment, and death) to estimate long-term costs and health outcomes. The model uses a time horizon equivalent to the life expectancy for this population. Clinical outcomes of trastuzumab emtansine (T-DM1) were taken from the KATHERINE clinical trial. Only direct medical costs associated with the pharmacotherapy and follow-up in each health state were included. Monetary valuation was performed using official databases for Colombia and expressed in 2021 Colombian pesos (COP). Health outcomes were expressed as quality-adjusted life years (QALYs). The discount rate was 5% per year for the costs and outcomes. Deterministic and probabilistic sensitivity analysis were performed.

Results: The expected costs were higher for T-DM1 than for trastuzumab: COP$ 300 million (USD 80.147,68), compared to COP$ 272 million (USD 72.667,23), but T-DM1 therapy offers better results: 10.48 QALYs vs 9.45, generating an ICER of COP$ 27.433.214 (USD 7.329,02) per QALY gained. The probabilistic sensitivity analysis shows that for a willingness to pay of COP$ 50 million (USD 13.357,94) per QALY gained, the probability that the intervention will be cost-effective is almost 80%.

Conclusion: From the perspective of the Colombian health system, T-DM1 is a cost-effective strategy compared to trastuzumab in the adjuvant treatment of adult patients with HER2+ early breast cancer who have residual invasive disease after neoadjuvant therapy compared with the 3 GDP per capita threshold (COP$ 61.999.878/USD 16.563,82).