- Indolent systemic mastocytosis (ISM) is the most common subtype of SM and can progress to higher burden disease in up to 18% of cases.
Avapritinib
PIONEER trial
S/E: Photosensitivity, edema, cognitive effects
25% of patients on POINEER was on 50mg dose, which is associated with higher rate of AEs
Bezuclastinib
SUMMIT trial
A global, randomized, double-blind, placebo-controlled, 3-part phase 2 clinical trial of bezuclastinib in adult patients with nonadvanced systemic mastocytosis
SUMMIT Trial: Bezuclastinib in NonAdvSM Patients - Summary Report
Executive Summary
The SUMMIT Part 2 trial evaluated bezuclastinib versus placebo in patients with non-advanced systemic mastocytosis (NonAdvSM). The study met its primary endpoint and all secondary endpoints with statistically significant results, demonstrating meaningful symptom reduction and objective measures of disease burden improvement.
Study Design
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SUMMIT Part 2 Study Design Overview
| Study Type |
Double-blind, placebo-controlled, randomized |
| Primary Endpoint |
Mean change in Total Symptom Score (TSS) at Week 24 |
| Treatment Arms |
Bezuclastinib 100mg QD + BSC vs Placebo + BSC |
| Randomization |
2:1 (Bezuclastinib:Placebo) |
| Study Duration |
24 weeks with open-label extension |
| Sample Size |
179 patients (119 bezuclastinib, 60 placebo) |
| Data Cutoff |
May 22, 2025 |
Patient Demographics and Baseline Characteristics
Patient Demographics and Baseline Characteristics
| Total Patients |
119 |
60 |
179 |
| Female (%) |
74 (62.2%) |
44 (73.3%) |
118 (65.9%) |
| Median Age (range) |
51 (24-73) |
52 (23-78) |
51 (23-78) |
| ECOG PS 0 (%) |
58 (48.7%) |
30 (50.0%) |
88 (49.2%) |
| ECOG PS 1 (%) |
50 (42.0%) |
26 (43.3%) |
76 (42.5%) |
| ECOG PS 2 (%) |
11 (9.2%) |
4 (6.7%) |
15 (8.4%) |
Disease Characteristics at Baseline
| Indolent SM (ISM) |
97 (81.5%) |
50 (83.3%) |
147 (82.1%) |
| Smoldering SM (SSM) |
8 (6.7%) |
4 (6.7%) |
12 (6.7%) |
| Bone Marrow Mastocytosis (BMM) |
14 (11.8%) |
6 (10.0%) |
20 (11.2%) |
| Median KIT D816V (%) |
0.22 (0-32) |
0.30 (0-34) |
0.25 (0-34) |
| Below Detection Limit |
28 (23.5%) |
12 (20.0%) |
40 (22.3%) |
| Median BM MC Burden (%) |
10 (1-75) |
10 (1-75) |
10 (1-75) |
| Median Serum Tryptase (ng/mL) |
40 (6-448) |
41 (7-692) |
40 (6-692) |
| Serum Tryptase < 20 ng/mL |
22 (18.5%) |
10 (16.7%) |
32 (17.9%) |
Primary and Secondary Endpoints Results
Primary and Secondary Endpoint Results
| Mean Change in TSS at Week 24 |
-24.32 (-27.56, -21.08) |
-15.41 (-19.58, -11.24) |
0.0002 |
Primary |
| ≥50% Reduction in Serum Tryptase |
87.4% |
0% |
<0.0001 |
Secondary |
| ≥50% Reduction in KIT D816V VAF |
Data not shown |
Data not shown |
<0.0001 |
Secondary |
| ≥50% Reduction in TSS |
Data not shown |
Data not shown |
0.0142 |
Secondary |
| ≥50% Reduction in Bone Marrow MC |
Data not shown |
Data not shown |
<0.0001 |
Secondary |
| ≥30% Reduction in TSS |
Data not shown |
Data not shown |
0.0004 |
Secondary |
| Mean Change in Most Severe Symptom Score |
Data not shown |
Data not shown |
0.0001 |
Secondary |
Treatment Effect Size Analysis
| Placebo-Adjusted Effect Size |
-8.91 (-13.56, -4.26) |
Clinically meaningful reduction |
| Percent Improvement vs Placebo |
57% improvement over placebo |
Substantial benefit vs control |
Safety Profile
Safety Overview
| Any TEAE |
116 (98.3%) |
53 (88.3%) |
| Serious AEs |
5 (4.2%) |
3 (5.0%) |
| Dose Reductions due to TRAEs |
13 (11.0%) |
0 |
| Discontinuations due to TRAEs |
7 (5.9%) |
0 |
| Grade 1 TEAEs |
70% of all TEAEs |
Not specified |
| ≥Grade 3 ALT/AST Elevations |
5.9% |
Not specified |
Treatment-Emergent Adverse Events (>10% in Bezuclastinib Arm)
| Hair color changes |
82 (69.5%) |
3 (5.0%) |
| Altered taste |
28 (23.7%) |
0 |
| Nausea |
26 (22.0%) |
8 (13.3%) |
| ALT/AST increased |
26 (22.0%) |
4 (6.6%) |
| Headache |
21 (17.8%) |
7 (11.7%) |
| Alopecia |
14 (11.9%) |
2 (3.3%) |
| ALP increased |
12 (10.2%) |
2 (3.3%) |
Case Studies Summary
Representative Case Study Outcomes
| Case 1: 44yo Woman with ISM |
67.9 |
27.8 |
68% |
91% (39.4 → 3.4 ng/mL) |
Discontinued all BSC meds in OLE, continued benefit >1 year |
| Case 2: 63yo Man with SM |
75.9 |
19.5 |
74% |
92% (95.5 → 7.9 ng/mL) |
Discontinued 3 BSC meds in OLE, continued benefit 32 weeks |
Market Opportunity and Pipeline
Bezuclastinib Development Pipeline and Market Opportunity
| SUMMIT (NonAdvSM) |
Non-Advanced Systemic Mastocytosis |
$2+ billion US annual |
TLR complete (Today) |
Mean change in TSS at Week 24 |
| PEAK (2nd-line GIST) |
Gastrointestinal Stromal Tumors |
$1+ billion US annual |
TLR expected EOY 2025 |
Progression Free Survival |
| APEX (AdvSM) |
Advanced Systemic Mastocytosis |
$300 million US annual |
TLR expected 2H 2025 |
Overall Response Rate |
Key Clinical Takeaways
Key Clinical Takeaways from SUMMIT Trial
| Efficacy |
24.3 point TSS reduction vs 15.4 point placebo reduction |
Clinically meaningful symptom improvement |
| Efficacy |
8.91 point placebo-adjusted effect (57% improvement) |
Superior to existing approved KIT inhibitors |
| Safety |
70% of TEAEs were Grade 1; only 5.9% discontinued |
Favorable tolerability for chronic use |
| Biomarkers |
87.4% achieved ≥50% serum tryptase reduction |
Objective evidence of disease modification |
| Clinical Utility |
Patients able to discontinue background medications |
Potential to simplify treatment regimens |
Regulatory and Commercial Timeline
Regulatory and Commercial Timeline
| SUMMIT TLR |
Complete (July 7, 2025) |
Primary trial success for NonAdvSM |
| NDA Submission |
Planned by end of 2025 |
Registration filing |
| PEAK TLR |
Expected EOY 2025 |
2nd indication data |
| APEX TLR |
Expected 2H 2025 |
3rd indication data |
| Expanded Access Program |
Currently active in US |
Patient access while pending approval |
Statistical Summary
Statistical Analysis Summary
| Primary Endpoint Power |
p = 0.0002 (highly significant) |
Strong evidence of efficacy |
| All Secondary Endpoints |
All met statistical significance |
Consistent benefit across measures |
| Effect Size |
Cohen’s d estimate: Large effect |
Substantial treatment benefit |
| Clinical Significance |
Exceeds minimal clinically important difference |
Meaningful patient benefit |
Data Source: Cogent Biosciences SUMMIT Trial Investor Webcast, July 7, 2025
Analysis Date: `r Sys.Date()# SUMMIT Trial: Bezuclastinib in NonAdvSM Patients - Summary Report
Avapritinib vs Bezuclastinib
This analysis compares the SUMMIT trial (bezuclastinib) with the PIONEER trial (avapritinib), both randomized, double-blind, placebo-controlled studies in patients with non-advanced systemic mastocytosis (NonAdvSM). Both trials met their primary endpoints but show distinct efficacy and safety profiles.
Study Design Comparison
Study Design Comparison: SUMMIT vs PIONEER
| Study Name |
SUMMIT Part 2 |
PIONEER Part 2 |
| Drug/Dose |
Bezuclastinib 100mg QD |
Avapritinib 25mg QD |
| Primary Population |
NonAdvSM (ISM, SSM, BMM) |
Indolent SM (ISM only) |
| Randomization |
2:1 |
2:1 |
| Sample Size |
179 (119 vs 60) |
212 (141 vs 71) |
| Primary Endpoint |
Mean change MS2D2 TSS at Week 24 |
Mean change ISM-SAF TSS at Week 24 |
| Study Duration |
24 weeks + OLE |
24 weeks + OLE |
| Status |
Complete (July 2025) |
Complete, FDA approved |
Patient Population Comparison
Patient Population Characteristics
| Total Randomized |
179 |
212 |
| Median Age |
51 years |
~50 years |
| Female (%) |
65.9% |
~65% |
| ECOG PS 0-1 (%) |
91.7% |
~95% |
| Prior KIT Inhibitor (%) |
12.3% |
Not specified |
| NonAdvSM Subtypes |
ISM 82.1%, SSM 6.7%, BMM 11.2% |
ISM 100% |
| Median Baseline TSS |
55.6 (MS2D2) |
~53 (ISM-SAF) |
| Median Serum Tryptase (ng/mL) |
40 |
Not specified |
| Median KIT D816V VAF (%) |
0.25 |
Not specified |
Primary Efficacy Results Comparison
Primary Endpoint Results Comparison
| Mean TSS Reduction at Week 24 |
-24.32 points (95% CI: -27.56, -21.08) |
-15.6 points (95% CI: -18.6, -12.6) |
| Placebo TSS Reduction |
-15.41 points (95% CI: -19.58, -11.24) |
-9.2 points (95% CI: -13.1, -5.2) |
| Placebo-Adjusted Effect |
-8.91 points (95% CI: -13.56, -4.26) |
-6.4 points |
| P-Value |
0.0002 |
0.003 |
| Effect Size Magnitude |
57% improvement over placebo |
41% improvement over placebo |
Secondary Efficacy Endpoints
Secondary Endpoints Comparison
| ≥50% TSS Reduction |
Not specified |
24.8% vs 9.9% placebo (p=0.005) |
| ≥30% TSS Reduction |
Not specified |
45.4% vs 29.6% placebo (p=0.009) |
| ≥50% Serum Tryptase Reduction |
87.4% vs 0% placebo (p<0.0001) |
53.9% vs 0% placebo (p<0.0001) |
| ≥50% KIT D816V VAF Reduction |
Met endpoint (p<0.0001) |
Met endpoint |
| ≥50% Bone Marrow MC Reduction |
Met endpoint (p<0.0001) |
Met endpoint |
| Mean TSS at 48 weeks (OLE) |
Not yet reported |
-20.2 points improvement |
Safety Profile Comparison
Safety Profile Comparison
| Any TEAE (%) |
98.3% (vs 88.3% placebo) |
90.8% (vs 93% placebo) |
| Serious AEs (%) |
4.2% (vs 5.0% placebo) |
5.0% (vs 11.3% placebo) |
| Discontinuation due to TRAEs (%) |
5.9% (vs 0% placebo) |
0.7% (vs 0% placebo) |
| Dose Reductions due to TRAEs (%) |
11.0% (vs 0% placebo) |
Not specified |
| Treatment Completion Rate (%) |
Not specified |
96.5% (vs 93% placebo) |
| Grade ≥3 AEs (%) |
Not specified |
21% (vs 21% placebo) |
Common Adverse Events Comparison
Common Adverse Events Comparison (>5% incidence)
| Hair color changes |
69.5% (vs 5% placebo) |
Not reported |
| Edema (peripheral/periorbital) |
Not specified as major AE |
12.8% combined (vs 4.2% placebo) |
| Nausea |
22.0% (vs 13.3% placebo) |
6.4% (vs 8.5% placebo) |
| Headache |
17.8% (vs 11.7% placebo) |
7.8% (vs 9.9% placebo) |
| Cognitive effects |
Not specified |
7.8% (vs 7.0% placebo) |
| Altered taste/Flushing |
23.7% altered taste (vs 0% placebo) |
≥5% flushing |
| Hepatic (ALT/AST elevation) |
22.0% (vs 6.6% placebo) |
Not major concern |
| Alkaline phosphatase elevation |
10.2% (vs 3.3% placebo) |
Increased (≥5%) |
Efficacy Superiority Analysis
Bezuclastinib Efficacy Advantages vs Avapritinib
| Absolute TSS Reduction |
24.3 vs 15.6 points (56% greater) |
Clinically meaningful difference |
| Placebo-Adjusted Effect |
8.9 vs 6.4 points (39% greater) |
Substantial additional benefit |
| Magnitude of Benefit |
Larger absolute and relative benefit |
Bezuclastinib more effective |
| Statistical Significance |
Stronger (p=0.0002 vs p=0.003) |
More robust statistical evidence |
| Tryptase Response Rate |
87.4% vs 53.9% (62% relative advantage) |
More patients achieve biomarker response |
| Clinical Advantage |
Superior symptom control |
Better patient outcomes expected |
Safety Profile Analysis
Safety Profile Analysis and Clinical Implications
| Discontinuation Rate |
Higher (5.9% vs 0.7%) |
Lower (0.7%) |
Bezuclastinib: more monitoring needed |
| Edema/Fluid Retention |
Not prominent |
Notable (12.8% edema) |
Avapritinib: edema management required |
| Cognitive Effects |
Not reported as major issue |
Similar to placebo (7.8%) |
Both drugs: acceptable cognitive safety |
| Hepatic Safety |
Manageable, reversible ALT/AST elevations |
Not major concern |
Bezuclastinib: requires LFT monitoring |
| Hair/Cosmetic Changes |
Common (69.5%) but reversible |
Not reported |
Bezuclastinib: cosmetic but reversible |
| Overall Tolerability |
Generally well-tolerated despite higher TEAE rate |
Well-tolerated with lower completion rate |
Both suitable for chronic treatment |
Biomarker Response Comparison
Biomarker Response Comparison
| ≥50% Serum Tryptase Reduction |
87.4% vs 0% placebo |
53.9% vs 0% placebo |
Bezuclastinib: 62% relative advantage |
| KIT D816V VAF Response |
Significant reduction achieved |
Achieved in majority |
Both effective |
| Bone Marrow Mast Cell Reduction |
Significant reduction achieved |
Achieved in majority |
Both effective |
| Objective Disease Modification |
Strong evidence across all measures |
Good evidence of disease modification |
Bezuclastinib: more patients respond |
Clinical Implications and Market Position
Clinical Implications and Strategic Considerations
| Regulatory Status |
NDA submission planned Q4 2025 |
FDA approved May 2023 |
Bezuclastinib following approved comparator |
| Target Population |
Broader NonAdvSM (ISM, SSM, BMM) |
ISM only |
Bezuclastinib targets broader patient population |
| Efficacy Positioning |
Superior TSS reduction and tryptase response |
Clinically meaningful benefit |
Bezuclastinib shows superior efficacy metrics |
| Safety Considerations |
Manageable with monitoring |
Well-characterized, manageable |
Both have manageable safety profiles |
| Clinical Utility |
May enable BSC medication discontinuation |
Established clinical experience |
Both enable improved patient management |
| Market Differentiation |
Potentially best-in-class efficacy |
First-to-market advantage |
Competition based on efficacy vs first-mover advantage |
Summary
Summary of Key Differences and Clinical Bottom Line
| Primary Efficacy |
56% greater TSS reduction |
Established efficacy |
Bezuclastinib shows superior symptom control |
| Biomarker Response |
62% higher tryptase response rate |
Proven disease modification |
Bezuclastinib achieves higher response rates |
| Patient Population |
Broader NonAdvSM subtypes |
ISM focus with deep experience |
Bezuclastinib addresses unmet need in SSM/BMM |
| Safety Profile |
Predictable, manageable AEs |
Lower discontinuation rate |
Both suitable for chronic use |
| Market Position |
Potential best-in-class |
First approved, established |
Market competition likely |
| Clinical Experience |
Newer data, recent results |
2+ years clinical experience |
Both represent major advances |
Conclusions Efficacy Advantage: Bezuclastinib
Superior symptom reduction: 24.3 vs 15.6 point TSS decrease (56% greater) Better biomarker response: 87.4% vs 53.9% tryptase reduction (62% advantage) Stronger statistical significance: p=0.0002 vs p=0.003
Population Advantage: Bezuclastinib
Broader indication: Includes SSM and BMM subtypes beyond ISM Addresses unmet need: No approved therapies for SSM
Safety Considerations
Avapritinib: Lower discontinuation rate, established safety profile Bezuclastinib: Higher efficacy with manageable safety, requires monitoring
Market Dynamics
Avapritinib: First-mover advantage, established market presence Bezuclastinib: Potential best-in-class positioning based on superior efficacy data
Clinical Bottom Line: Bezuclastinib demonstrates superior efficacy across multiple endpoints compared to avapritinib, with the potential to set a new standard of care for NonAdvSM patients, while avapritinib maintains advantages in established clinical experience and current market access.
Elenestanib
- a novel oral next generation TKI with limited CNS penetration.
TL-895
TELIO study
- This study evaluates TL-895, a potent, orally-available and highly selective irreversible tyrosine kinase inhibitor for the treatment of Myelofibrosis (Cohorts 1-3) or Indolent Systemic Mastocytosis (Cohort 5).