Trastuzumab deruxtecan demonstrates tolerable long-term safety, supporting its clinical benefit vs trastuzumab emtansine for patients with HER2–positive metastatic breast cancer, according to an updated analysis of the DESTINY-Breast03 trial presented at the 2022 ASCO Annual Meeting.

“In the DESTINY-Breast03 primary analysis, [trastuzumab deruxtecan] showed superiority over [trastuzumab emtansine] in patients with [with HER2–positive metastatic breast cancer], with a significant improvement of progression-free survival… and a safety profile consistent with prior studies,” explained Erika Hamilton, MD, Sarah Cannon Research Institute, Tennessee Oncology, Nashville, TN, and colleagues.

This analysis explores the long-term safety of trastuzumab deruxtecan in the DESTINY-Breast03 trial, which randomized patients in a 1:1 ratio to receive either trastuzumab or trastuzumab emtansine. Treatment–emergent adverse events were evaluated, and end points included time to event, duration of event, and resolution.

At data cutoff (September 7, 2021), 45.1% (n = 116) of patients remained on trastuzumab deruxtecan and 14.9% (n = 39) patients remained on trastuzumab emtansine. The median duration of treatment was 16.1 months and 6.9 months, respectively.

For trastuzumab deruxtecan, the rates of any grade, grade ≥3, and serious adverse events (AEs) were 99.6%, 53.3%, and 21%. For trastuzumab emtansine, these rates were 95.4%, 49.8%, and 19.2%, respectively. Exposure-adjusted incidence rates for grade ≥3 and serious AEs were lower for trastuzumab deruxtecan vs trastuzumab emtansine (0.42 vs 0.70 and 0.17 vs 0.27). The majority of treatment–emergent AEs (≥20%) were hematologic or gastrointestinal.

Median time to treatment–emergent AEs associated with drug discontinuation was 224 days for trastuzumab deruxtecan vs 147 days for trastuzumab emtansine. The median time to dose reduction was 96 days vs 19 days, respectively.

Median time to first onset of any grade AEs with trastuzumab deruxtecan vs trastuzumab emtansine 70 vs 42 days for anemia, 196 vs 168 days for fatigue, 74.5 vs 92 days for leukopenia, and 64 vs 105 days for neutropenia. Grade ≥3 AEs with trastuzumab deruxtecan vs trastuzumab emtansine were 6.6% vs 0.4% for nausea and 1.6% vs 0.8% for vomiting, respectively.

For trastuzumab deruxtecan, rates of nausea, vomiting, and alopecia were highest in cycle 1 and lower in subsequent cycles. In both treatment arms, rates of hematologic AEs were lower in earlier cycles.

Rates of treatment-related interstitial lung disease (ILD)/pneumonitis were 10.9% with trastuzumab deruxtecan vs 1.9% with trastuzumab emtansine. Median time to first ILD/pneumonitis event was 5.9 vs 9.5 months, respectively.

“This longer safety update reinforces the consistent safety profile of [trastuzumab deruxtecan], supporting the clinical benefit of [trastuzumab deruxtecan] over ][trastuzumab emtansine in patients with [HER2–positive metastatic breast cancer],” concluded Dr Hamilton and colleagues.

Source:

Hamilton EP, Bragaia VPH,  Yeo W, et al. Trastuzumab deruxtecan (T-DXd) versus trastuzumab emtansine (T-DM1) in patients (pts) with HER2-positive (HER2+) unresectable and/or metastatic breast cancer (mBC): Safety follow-up of the randomized, phase 3 study DESTINY-Breast03. Presented at: the 2022 ASCO Annual Meeting; June 3-7, 2022; Chicago, IL. Abstract 1000.