Gastrointestinal stromal tumors (GIST) are the most common mesenchymal malignancies of the gastrointestinal tract and are predominantly driven by activating KIT mutations. While KIT-targeted tyrosine kinase inhibitors have transformed patient outcomes, resistance inevitably develops through the emergence of heterogeneous secondary KIT mutations, limiting the effectiveness of currently available therapies.

Bezuclastinib is a selective type 1 KIT inhibitor designed to target a broad spectrum of primary and secondary KIT resistance mutations. When combined with sunitinib, a type 2 KIT inhibitor, the regimen provides complementary inhibition of resistance pathways, creating a rationale for enhanced antitumor activity in advanced KIT-mutant GIST. The Phase III Peak study evaluated this dual KIT inhibition strategy against standard second-line sunitinib monotherapy in patients whose disease had progressed following prior imatinib treatment.

Efficacy Outcomes:

Progression-free Survival (PFS)

• Median PFS: 16.5 months with bezuclastinib + sunitinib versus 9.2 months with sunitinib alone 

• 50% reduction in the risk of progression or death (HR: 0.50; p < 0.0001)  

Objective Response Rate (ORR)

• ORR: 46% with bezuclastinib + sunitinib and 26% with sunitinib monotherapy 

• Statistically significant improvement (p < 0.0001) 

Overall Survival (OS): data remain immature as of the September 30, 2025 data cutoff. 

Safety Outcome:

• Overall adverse event rates were generally similar between treatment arms. 

• Grade ≥3 adverse events were comparable between the combination and monotherapy groups. 

• No significant increase in common sunitinib-associated toxicities was observed with the addition of bezuclastinib. 

• Higher rates of Grade ≥3 ALT/AST elevations and anemia were observed with the combination and were manageable with dose modification. 

• ALT/AST elevations led to bezuclastinib dose reductions in 13.2% and discontinuations in 1.5% of patients in the combination arm; all Grade 3 hepatic AEs resolved; no Grade 4 events occurred. 

• Additional treatment-emergent AEs leading to discontinuation of either drug in >1 patient in the combination arm were neutropenia (2.9%) and diarrhea (1%). 

• No treatment-related AEs led to death in the combination arm.

KOL Insights

“The findings are particularly encouraging, demonstrating a consistent clinical benefit across all mutational subgroups of patients with advanced GIST. Equally important, the safety profile of bezuclastinib in combination with sunitinib appears generally consistent with what has been observed historically with sunitinib monotherapy, supporting its tolerability in clinical practice. With the recent FDA Priority Review designation, this regimen has the potential to become an important new treatment option for patients with advanced GIST, addressing a significant unmet need in this setting.”– Expert Opinion

“These results represent a significant milestone in the treatment of advanced GIST. For the first time in decades, a therapeutic approach has demonstrated outcomes that surpass those achieved with standard second-line sunitinib. The magnitude of benefit is not only statistically compelling but also clinically meaningful, with the potential to redefine the treatment paradigm and establish a new standard of care for patients in this setting.”– Expert Opinion

Conclusion

Gastrointestinal stromal tumors (GISTs) are rare, accounting for less than 1% of all gastrointestinal tumors. However, they are the most common mesenchymal neoplasms of the gastrointestinal tract, with the majority originating in the stomach (60–70%), followed by the small intestine and other gastrointestinal locations.

The Phase III Peak study demonstrated that combining bezuclastinib with sunitinib significantly improves clinical outcomes in patients with advanced GIST following prior imatinib therapy. Importantly, these substantial efficacy gains were achieved without a major increase in overall toxicity, and no new safety concerns emerged. The manageable safety profile, coupled with robust improvements in disease control, positions bezuclastinib plus sunitinib as a potential new second-line standard of care for patients with advanced KIT-mutant GIST. As overall survival data mature, the Peak study may represent a pivotal step forward in overcoming treatment resistance in GIST.