OBJECTIVES : In Turkey, 5,930 people are affected by HER2-positive breast cancer in 2019. Trastuzumab emtansine (T-DM1) is an antibody-drug conjugate being studied in HER2-positive cancers and it is designed to target and inhibit HER2 signaling. The aim of the cost effectiveness (CE) model is to assess the CE of T-DM1 versus: Capecitabine plus lapatinib (LapCap), trastuzumab plus capecitabine (TrastCap), capecitabine alone (Cap) and vinorelbine alone (Vin) for patients previously treated with taxane and trastuzumab in HER2-positive mBC from the perspective of Social Security Institution (national payer) in Turkey.

METHODS : T-DM1 is compared with all relevant mBC treatments using a partitioned survival cost effectiveness model. The model considers three health states: progression-free survival (PFS), progression (PD), and death. Transition probabilities determine the movement of patients between these health states. The model cycle length is one week. Time horizon is 7 years in the base scenario due to the progressive state of metastatic breast cancer. Discount rate of 3.5% applied for utilities & costs. The model findings validated with Probabilistic Sensitivity Analysis (PSA).

RESULTS : The main model outcome is determined according to the incremental cost-effectiveness ratio (ICER) based on the life years gained. Base case model analysis shows an ICER of T-DM1 vs. LapCap as 165,301TRY. The results of economic comparison based on the systematic review and indirect treatment comparison show a life years gained ICER of T-DM1 vs. TrastCap as 91,412TRY, T-DM1 vs. Cap as 119,146TRY and T-DM1 vs Vin as 116,239TRY. In conclusion, trastuzumab emtansine is a cost effective option compare to a lapatinib plus capecitabine regimen.

CONCLUSIONS : Regardless of treatment line, trastuzumab emtansine regime is cost effective compared to LapCap regimen in Turkey. Probabilistic sensitivity analysis concludes that ICER compared to LapCap is 166,057TRY which is similar to base-case.