SINGAPORE – Heavily pretreated patients with EGFR-mutated non–small cell lung cancer (NSCLC) may experience a clinically meaningful benefit with the antibody-drug conjugate (ADC) patritumab deruxtecan (HER3-DXd), new phase 2 trial results suggest.
In the trial, almost 30% of patients receiving HER3-DXd achieved an objective response, and patients’ median overall survival approached 1 year.
HER3-DXd has “emerged as a promising therapy” in this patient population, “for whom available treatment options provide only limited efficacy,” concluded lead study author Helena A. Yu, MD, from Memorial Sloan Kettering Cancer Center, New York City, who presented findings from the HERTHENA-Lung01 trial at the 2023 World Conference on Lung Cancer.
The results were simultaneously published in the Journal of Clinical Oncology.
Acquired resistance to therapy among heavily pretreated patients with EGFR-mutated NSCLC is “universal,” Dr. Yu explained. The mechanisms of resistance to first-line osimertinib are also “diverse” and hard to identify. Salvage therapies after failed EGFR tyrosine kinase inhibitor (TKI) therapy and platinum-based chemotherapy offer “only a limited and transient and clinical benefit,” she said.
And with limited treatment options available to patients resistant to TKIs, there is a “high unmet medical need” for new therapies, said Helena Linardou, MD, PhD, who was not involved in the study.
HER3-DXd consists of a fully human anti-HER3 immunoglobulin G1 monoclonal antibody (patritumab) attached to a topoisomerase I inhibitor payload (DXd) via a tetrapeptide-based cleavable linker.
HER3, Dr. Linardou explained, is a “biologically and clinically important target” in NSCLC. It is highly expressed in NSCLC, upregulated in TKI-resistant EGFR-mutated NSCLC, and is associated with a poor prognosis.
After promising phase 1 data, Dr. Yu and colleagues conducted a phase 2 trial in patients with advanced EGFR-mutated NSCLC who had progressed on systematic therapy and had received EGFR TKI and platinum-based chemotherapy. Patients could have active or previously treated asymptomatic brain metastases.
Patients were initially randomized either to a fixed-dose arm of HER3-DXd 5.6 mg/kg once every 3 weeks or an uptitration arm with doses escalating from 3.2 mg/kg to 4.8 mg/kg to 6.4 mg/kg over three cycles. However, Dr. Yu noted, enrollment in the uptitration arm closed early based on a “benefit-risk assessment.”
The current findings focus on the 225 patients in the fixed-dose arm.
About half of patients had a history of central nervous system metastasis, and patients had a median of three prior lines of systemic therapy. Most patients (92.9%) had previously received a third-generation EGFR TKI, about 40% had received immunotherapy, and all had received platinum-based chemotherapy.
After a median follow-up of 18.9 months, the confirmed objective response rate with HER3-DXd across the whole patient population was 29.8%. The median duration of response was 6.4 months, median progression-free survival was 5.5 months, and median overall survival was 11.9 months.
The results were virtually identical when looking only at patients who had received a third-generation EGFR TKI versus any EGFR TKI. Response rates were also similar regardless of the driver of EGFR TKI resistance.
Among the 30 patients with measurable brain metastases at baseline, 33.3% had a confirmed objective response to therapy. In this group, the disease control rate was 76.7% and the intracranial duration of response was 8.4 months.
To identify biomarkers of response to HER3-DXd, the team stratified the patients by baseline tumor HER3 membrane H-scores. Dr. Yu and colleagues found no differences in the likelihood of having a complete or partial response, stable disease, or progressive disease based on HER3 expression at study entry.
Looking at the safety of the ADC, only 7.1% of patients experienced a treatment-emergent adverse event associated with treatment discontinuation, but close to half of patients (45.3%) experienced a grade 3 or higher treatment-emergent adverse event. Interstitial lung disease, for instance, occurred in 5.3% of patients, including one patient who died.
The safety profile of HER3-DXd in this population appeared to be consistent with previous reports, Dr. Yu noted.
Overall, the findings suggest that “HER3-DXd provided clinically meaningful and durable efficacy” in patients with advanced EGFR-mutant NSCLC that has progressed after EGFR TKI and platinum-based chemotherapy, Dr. Yu said.
“Efficacy was observed across diverse mechanisms of resistance and across a broad range of pretreatment tumor HER3 expression” and the ADC demonstrated “clinically meaningful intracranial antitumor activity,” she added.
Dr. Linardou agreed that the current results suggest that HER3-DXd was associated with a “meaningful and durable efficacy,” including in patients with intracranial metastases, and she pointed to its “easy dosing schedule” and activity across patient subgroups.
However, she noted that, despite the researchers’ best efforts with the data available, “we don’t have a biomarker of activity,” which is a “general issue with ADCs.”
Still, Dr. Linardou said, “HER3 is now a clinically actionable therapeutic target, and this is a great bonus.”
The study was sponsored by Daiichi Sankyo. Dr. Yu declared relationships with AstraZeneca, Daiichi Sankyo, Blueprint Medicines, Janssen, C4 Therapeutics, Cullinan Oncology, Black Diamond Therapeutics, Taiho Oncology, and others. Other authors declare numerous relationships.
A version of this article first appeared on Medscape.com.