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.