CRESTONE: A Phase II Study of the Efficacy and Safety of the HER3 Monoclonal Antibody, Seribantumab, in Solid Tumors With Neuregulin-1 ( NRG1 ) Fusions

PURPOSE Neuregulin-1 ( NRG1 ) fusions are rare but actionable oncogenic drivers in solid tumors. Seribantumab is a fully human anti-HER3 IgG2 monoclonal antibody. In this report, we present the antitumor activity and safety data of seribantumab from the CRESTONE study (ClinicalTrials.gov identifier: NCT04383210 ). PATIENTS AND METHODS This was a prospective phase II clinical study in which patients with advanced solid tumors harboring an NRG1 fusion received seribantumab at a dose of 3,000 mg intravenously once weekly. The primary end point was objective response rate (ORR) by RECIST v1.1. Secondary end points included safety, duration of response, progression-free survival (PFS), overall survival (OS), and disease control rate (DCR). The study was terminated before full enrollment because of sponsor decision, unrelated to safety or efficacy. RESULTS A total of 54 patients with nine different tumor types featuring 19 different NRG1 fusion partners were enrolled. For the 29 patients included in the primary efficacy analysis, the investigator-assessed ORR was 34.5% (95% CI, 17.9 to 54.3), with a DCR of 79% (95% CI, 60 to 92). The median PFS was 5.4 (95% CI, 3.9 to 10.8) months; the median OS was 20.3 (95% CI, 10.2 to not reached) months. In patients with non–small cell lung cancer, eight of 22 achieved response (ORR, 36.4%). Adverse events (AEs) were mostly grade 1 or 2. The most common treatment-related AEs were diarrhea (39%), fatigue (32%), and nausea (22%). CONCLUSION These results support the antitumor activity and safety of seribantumab in patients with advanced solid tumors harboring NRG1 fusions.