Presentation (CTI)

OBJECTIVES: Trastuzumab Deruxtecan (T-DXd) recently received financial approval by the Portuguese medicine’s authority to be used in second line HER2-positive metastatic breast cancer (2L-HER2+mBC). Before this, Trastuzumab Emtasine (T-DM1) was used instead. We aimed to compare our hospital’s T-DM1 historical clinical data with the most recent T-DXd data.
METHODS: Clinical and pharmacy records from all patients treated with T-DXd and T-DM1 until 31 May 2025 were analyzed. Those in the indication of 2L-HER2+mBC were selected. Time until treatment discontinuation (TTD) of all cause’s estimates were obtained through Kaplan-Meier survival analysis and log-rank test was used for comparison. Immature data was extrapolated with different parametric survival distributions and AIC criteria was used for best fit.
RESULTS: A total of 90 patients, all women, were selected (T-Dxd, n=11 vs T-DM1, n=79). No differences between groups in age [median (range), 45.9 (27.4,71.2) vs 54.1 (31.2,90.1), years, p=0.264] and treatment time [median (range), 6.5 (1.4,10.8) vs 5.0 (0.7,48.9), months, p=0.514] were noticed. Treatment discontinuation occurred in 2/11, T-Dxd group (1/11, progression disease - PD; 1/11 lost for follow-up) vs 75/79, T-DM1 group (59/79, PD; 12/79, Toxicity/Serious infection; 4/79, Death). Median TTD was 5.0 months (95%CI, 4.2-6.5), T-DM1 group, not reached, T-Dxd group, log-rank test (Chi-squared=5.6, p=0.02). To estimate median TTD for T-Dxd group, an exponential parametric survival model showed the best fit (AIC=20.15). Extrapolated median TTD for T-Dxd was 23.8 months (95%CI, 5.96-97.1). The estimated probability of a patient being in treatment at 48 months was 24.7% (95%CI, 0.19-69.7) for T-Dxd (extrapolated) compared to 2.5% (95%CI, 0.4-13.8) for T-DM1 (observed).
CONCLUSIONS: Although our T-Dxd data was immature, extrapolation and comparison analysis with historical T-DM1 data showed results in line with published clinical trials and real-world studies. Early clinical outcomes’ validation is crucial for approaching real-world cost-effectiveness analysis.