8-K: Cogent Biosciences: Bezuclastinib Shines in SUMMIT & APEX Trials

Cogent Biosciences announced positive full results from its SUMMIT trial in nonadvanced systemic mastocytosis and top-line results from its APEX trial in advanced systemic mastocytosis for bezuclastinib.

Summary

• Cogent Biosciences presented full results from the SUMMIT clinical trial of bezuclastinib in patients with nonadvanced systemic mastocytosis (NonAdvSM) on December 6, 2025.
• Bezuclastinib demonstrated clinically meaningful and highly statistically significant improvements across primary and all key secondary endpoints in the SUMMIT trial, including patient-reported symptoms and objective measures of mast cell burden.
• At 24 weeks in the SUMMIT trial, bezuclastinib showed a mean change in Total Symptom Score (TSS) of -24.3 (-43%) compared to -15.4 (-29%) for placebo (p<0.001).
• In the SUMMIT trial, 34.3% of patients achieved a 50% reduction in TSS with bezuclastinib versus 18.1% with placebo (p=0.01) at 24 weeks.
• Follow-up data through 48 weeks in SUMMIT showed a mean change in TSS of -32.0 (-54%) and 56.4% of patients achieving a 50% reduction in TSS.
• Objective disease markers in SUMMIT at week 24 showed 87.4% of patients achieved a 50% reduction in serum tryptase levels, 75.6% a 50% reduction in bone marrow mast cells, and 85.7% a 50% reduction in KIT D816V variant allele frequency, all statistically significant compared to placebo.
• Cogent Biosciences announced positive top-line results from the APEX clinical trial of bezuclastinib in patients with advanced systemic mastocytosis (AdvSM) on December 8, 2025.
• The APEX trial demonstrated clinically meaningful results, with a primary endpoint of 57% Overall Response Rate (ORR) per mIWG-MRT-ECNM criteria and 49% ORR (CR+CRh+PR) per mIWG criteria.
• A key secondary endpoint in APEX showed an 80% ORR per pure pathological response (PPR) criteria.
• In the APEX trial, median time to achieve response was 2.0 months, and median duration of response is not yet mature.
• Objective disease markers in APEX showed 89% of patients with a 50% reduction in serum tryptase, 89% with a 50% reduction in bone marrow mast cells, and 91% with a 50% reduction in KIT D816V variant allele frequency.
• This marks the third positive pivotal trial result for bezuclastinib in 2025, following SUMMIT and the PEAK trial in GIST patients.

Sentiment

Score: 9

Explanation: The filing reports highly positive and statistically significant clinical trial results for bezuclastinib in two pivotal studies (SUMMIT and APEX) for systemic mastocytosis, a rare and serious disease. The drug demonstrated strong efficacy across multiple endpoints and patient populations, coupled with a manageable safety profile. The successful completion of three pivotal trials in 2025 and the stated intent to submit an NDA in H1 2026 significantly de-risk the asset and indicate strong commercial potential.

Positives

• Bezuclastinib demonstrated clinically meaningful and highly statistically significant improvements across primary and all key secondary endpoints in the SUMMIT trial for NonAdvSM.
• Significant symptomatic improvement was observed in SUMMIT, with a -43% mean change in TSS at 24 weeks for bezuclastinib versus -29% for placebo (p<0.001).
• Sustained symptomatic improvement was shown in SUMMIT, with a -54% mean change in TSS at 48 weeks and 56.4% of patients achieving a 50% reduction in TSS.
• Rapid, deep, and sustained improvement on objective disease markers of mast cell burden was seen in SUMMIT, including significant reductions in serum tryptase (87.4%), bone marrow mast cells (75.6%), and KIT D816V variant allele frequency (85.7%).
• Bezuclastinib showed consistent efficacy in SUMMIT subgroups, including patients with Smoldering Systemic Mastocytosis and those previously treated with avapritinib.
• The safety profile in SUMMIT was favorable, with the majority of treatment emergent adverse events (TEAEs) being low grade (98.3% for bezuclastinib) and serious AEs occurring in only 4.2% of patients.
• Positive top-line results were achieved in the APEX trial for AdvSM, demonstrating clinically meaningful outcomes.
• High Overall Response Rates (ORR) were observed in APEX, with 57% per mIWG criteria and 80% per pure pathological response (PPR) criteria.
• Rapid onset of response in APEX, with a median time to achieve response of 2.0 months.
• Clear and clinically significant reductions in objective disease markers for AdvSM patients in APEX, including serum tryptase (89%), bone marrow mast cells (89%), and KIT D816V variant allele frequency (91%).
• The safety and tolerability in APEX were good, with no patients discontinuing due to treatment-related adverse events (TRAEs) and only 14.8% requiring dose reduction.
• This is the third positive pivotal trial result for bezuclastinib in 2025, indicating broad potential for the drug.

Negatives

• The most frequent treatment emergent adverse events (TEAEs) in the SUMMIT trial for bezuclastinib included hair color change (69.5%), altered taste (23.7%), nausea (22.0%), and ALT/AST elevations (22.0%; Gr 3, 5.9%).
• Discontinuations due to treatment-related AEs occurred in 5.9% of patients treated with bezuclastinib in SUMMIT, all due to ALT/AST elevations.
• The most frequent treatment related adverse events (TRAEs) in the APEX trial included hair color change (30.9%), neutropenia (29.6%), altered taste (28.4%), thrombocytopenia (24.7%), and ALT/AST elevations (20.9%).
• 14.8% of patients in the APEX trial required dose reduction due to TRAEs.

Risks

• New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties.
• The Company may not actually achieve the forecasts or milestones disclosed in its forward-looking statements, and undue reliance should not be placed on them.
• Forward-looking statements are subject to material risks and uncertainties, including those set forth under the caption Risk Factors in the Company's most recent Annual Report on Form 10-K, Quarterly Report on Form 10-Q, and subsequent SEC filings.

Future Outlook

Cogent Biosciences expects to submit a New Drug Application (NDA) to the U.S. Food and Drug Administration (FDA) for bezuclastinib in advanced systemic mastocytosis (AdvSM) during the first half of 2026. Additionally, the company plans to present detailed data from the APEX trial at an upcoming scientific meeting in the first half of 2026.

Management Comments

• Cogent expects to submit a new drug application (NDA) to the U.S. Food and Drug Administration (FDA) for bezuclastinib in AdvSM during the first half of 2026.
• Cogent plans to present detailed data from the APEX trial at an upcoming scientific meeting in the first half of 2026.

Industry Context

The positive results for bezuclastinib in both nonadvanced and advanced systemic mastocytosis position Cogent Biosciences as a significant player in the treatment of mast cell disorders. Systemic mastocytosis is a rare disease with unmet needs, and these results suggest bezuclastinib could offer a new, effective therapeutic option, potentially expanding the market and competing with existing or developing therapies, such as avapritinib, which was mentioned as a prior treatment for some patients in the SUMMIT trial.

Stakeholder Impact

• Shareholders: Likely positive impact due to strong clinical data, increased probability of regulatory approval, and potential for future revenue generation.
• Patients: Significant positive impact by offering a new, effective treatment option for both nonadvanced and advanced systemic mastocytosis, a rare disease with unmet medical needs.
• Healthcare Providers: Provides a new therapeutic tool for managing systemic mastocytosis, potentially improving patient outcomes.
• Regulatory Authorities: Will review the submitted NDA, potentially leading to market approval for a new drug.

Next Steps

• Submit a New Drug Application (NDA) to the U.S. Food and Drug Administration (FDA) for bezuclastinib in AdvSM during the first half of 2026.
• Present detailed data from the APEX trial at an upcoming scientific meeting in the first half of 2026.
• Complete full analysis of the APEX Part 2 data.

Key Dates

Recommendation

The company has announced overwhelmingly positive results from two pivotal clinical trials (SUMMIT and APEX) for bezuclastinib in systemic mastocytosis, a rare disease with significant unmet needs. These results demonstrate strong efficacy across primary and secondary endpoints, including patient-reported symptoms and objective disease markers, with a manageable safety profile. The successful completion of three pivotal trials in 2025 (SUMMIT, APEX, and PEAK in GIST) significantly de-risks the drug's development and paves the way for an NDA submission in AdvSM in H1 2026. This progress indicates a high probability of market approval and substantial commercial potential, making it a compelling investment opportunity.

Keywords

bezuclastinib, systemic mastocytosis, NonAdvSM, AdvSM, clinical trial, SUMMIT, APEX, FDA, NDA, oncology, rare disease, mast cell, KIT D816V