Trastuzumab Emtansine (T-DM1) and Survival Outcomes in HER2-Positive Metastatic Breast Cancer: A Single-Center Experience

Purpose: To describe real-world outcomes of trastuzumab emtansine (T-DM1) in patients with HER2-positive metastatic breast cancer and to explore clinical factors associated with survival. Methods: This retrospective single-center cohort included women with HER2-positive metastatic breast cancer who received at least one cycle of T-DM1 between March 2020 and January 2025 at Adana City Training and Research Hospital. Demographic, clinicopathologic and treatment-related data were collected from electronic health records. Progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan–Meier method, and prespecified subgroups were compared using two-sided log-rank tests. Results: Sixty-one patients were included; median age at T-DM1 initiation was 52 years (range, 34–82). All had received prior trastuzumab-based therapy, most had been treated with taxanes and pertuzumab, and T-DM1 was used predominantly as second-line treatment. Median PFS was 8.1 months (95% CI, 6.9–9.2) and median OS was 24.5 months (95% CI, 22.7–26.3). The objective response rate was 55.7%, with stable disease in 8.2%. ECOG performance status was the strongest prognostic factor. Patients with ECOG 0–1 had longer PFS (10.9 vs 5.9 months) and OS (30.3 vs 10.5 months) than those with ECOG 2. Median OS was shorter in patients with brain/CNS metastases than in those without (8.9 vs 25.1 months), while PFS did not differ meaningfully between these groups. Conclusion: In this real-world cohort, T-DM1 provided PFS, OS and response rates comparable to those reported in clinical trials, in a population previously treated with trastuzumab- and pertuzumab-based first-line therapy and receiving T-DM1 predominantly as second-line treatment. Performance status and brain/CNS involvement were key determinants of outcome. These findings emphasize the prognostic role of performance status and the continuing need for more effective approaches in patients with brain/CNS metastases.