Real‐World Safety and Efficacy of Biosimilar Trastuzumab Emtansine (T‐DM1) in HER2‐Positive Breast Cancer: A Prospective Single‐Institution Study From India

Background Trastuzumab emtansine (T‐DM1) represents an advancement in HER2‐targeted therapy, offering a unique combination of trastuzumab′s specificity and the cytotoxic potency of maytansine. It demonstrates therapeutic efficacy across the spectrum of breast cancer, including both early‐stage and advanced disease. With the emergence of biosimilar formulations, there is a growing need to generate real‐world evidence supporting their clinical performance. This study investigates the effectiveness and safety of a T‐DM1 biosimilar in routine oncology practice across adjuvant and metastatic HER2‐positive breast cancer populations. Methods In this prospective, single‐institute study conducted at a tertiary oncology center in India, 116 patients with HER2‐positive breast cancer (51 adjuvant and 65 metastatic) received T‐DM1 biosimilar (Ujvira) between June 2021 and October 2023. Outcomes assessed included overall response rate (ORR), progression‐free survival (PFS), overall survival (OS), and treatment‐emergent adverse events (AEs), graded using CTCAE v5.0. Results In the metastatic cohort, ORR was 63.4%, median PFS was 8.0 months (95% CI: 5.8–10.2), and estimated median OS was 18.0 months (95% CI: 16.1–19.9). Clinical benefit rate was 75%. In the adjuvant cohort, 62.7% completed the planned 14 cycles, and treatment was well tolerated. Grade ≥ 3 AEs occurred in 6.9% of all patients, with fatigue and thrombocytopenia being the most common AEs. No unexpected safety signals were observed. Conclusion T‐DM1 biosimilar showed outcomes consistent with those reported for the originator in real‐world settings, supporting its broader adoption in both early and advanced HER2‐positive breast cancer. Its affordability may improve access and outcomes in resource‐limited settings.