Trastuzumab deruxtecan in HER2-positive and low breast cancer: Real-world outcomes from the Indian perspective (TREAD-IN study)

Objectives: Trastuzumab deruxtecan (T-DXd) has demonstrated significant efficacy in human epidermal growth factor Receptor 2 (HER2)-positive metastatic breast cancer (mBC). However, real-world data, particularly from diverse populations like India, are limited. This study aimed to assess the real-world safety and efficacy of T-DXd in Indian patients with HER2-positive mBC. Material and Methods: This retrospective, single-centre study analysed medical records of 24 patients with HER2-positive mBC treated with T-DXd at a tertiary care centre in India. Patients received T-DXd 5.4 mg/kg every 3 weeks. Data collected included demographics, disease characteristics, treatment details, response rates (per RECIST 1.1), progression-free survival (PFS), and adverse events (AEs). Results: The median patient age was 50 years (range 36–71). The majority (86.9%) were still on treatment at data cutoff (median follow-up 6 months). The overall response rate (ORR) was 66.7% (complete response CR 4.2%, partial response PR 62.5%), with a disease control rate (DCR) of 87.5%. The median PFS was not reached, with an estimated 1-year PFS of 72.7% ± 12.5%. The most common AEs were nausea (45.8%), fatigue (33%), neutropenia (25%), and vomiting (20.8%). Interstitial lung disease (ILD) occurred in 3 patients (12.5%). The observed PFS was similar for patients treated with T-DXd in 2nd/3rd versus 4th+ lines. Conclusion: This real-world study demonstrates the efficacy and manageable safety profile of T-DXd in Indian patients with HER2-positive mBC, even in heavily pretreated patients and those receiving treatment in later lines, supporting its continued use in this population. The findings largely align with clinical trial data.