Leveraging ctDNA Subgroups and Clearance Metrics For Velzatinib in GIST

Michael C. Heinrich, MD, of Oregon Health and Science University, shares data from the phase 1/1b StrateGIST 1 study (NCT05489237) evaluating velzatinib, a next-generation KIT inhibitor developed to target the receptor tyrosine kinase mutations that drive 70% to 80% of gastrointestinal stromal tumors (GIST). Designed to overcome emerging drug resistance through advanced chemical engineering, the agent established efficacy and safety in first through fourth-line cohorts.

Concurrent data from the trial focuses on early-line clinical efficacy, Dr. Heinrich’s specific abstract investigates the utility of circulating tumor DNA (ctDNA) biomarkers. The study analyzed baseline KIT mutations in the blood to predict patient response and track tumor dynamics. Velzatinib demonstrated profound clinical activity in patients harboring baseline KIT exon 9 mutations, yielding a robust 44% objective response rate (ORR). Furthermore, the drug demonstrated broad-spectrum target inhibition across other common molecular subgroups, including exons 11, 13, 14, and 17, which achieved a collective ORR of approximately 20%.

The biomarker analysis also uncovered a novel prognostic indicator. Approximately 20% of the cohort had no detectable KIT mutations in their baseline ctDNA, and these specific individuals experienced significantly prolonged progression-free survival. The study defined “molecular clearance” as a 99% or greater reduction in the baseline KIT mutation load; 75% of patients across all molecular subgroups achieved this profound level of ctDNA clearance. Moving forward, these compelling outcomes will inform the design of upcoming phase 3 trials in the first- and second-line settings, with future analyses dedicated to fully understanding how early ctDNA clearance directly correlates with long-term survival outcomes.