CytomX's Varsetatug Masetecan Shows 32% Response Rate in Late-Line Colorectal Cancer—Phase 1 Data Highlights Emerging Potential

Phase 1 Expansion Data Reveals Strong Efficacy at Higher Doses

CytomX Therapeutics (NASDAQ: CTMX) announced new Phase 1 data for its EpCAM-targeted PROBODY® ADC, varsetatug masetecan (Varseta-M), in late-line metastatic colorectal cancer (CRC). The most recent results, as of January 16, 2026, indicate promising activity for heavily pretreated patients who have limited options left. Notably, the confirmed overall response rate (ORR) reached 32% at the 10 mg/kg dose, and 20% at the 8.6 mg/kg dose. These findings may represent a significant advance for this patient population, potentially setting the stage for future treatment protocols.

Clinically Meaningful Disease Control with Manageable Side Effects

The data also show a high disease control rate (DCR) across dosages, with 90% at 8.6 mg/kg and 84% at 10 mg/kg, illustrating Varseta-M's ability to stabilize disease in challenging clinical scenarios. Median progression-free survival (PFS) estimates were 7.1 months at 10 mg/kg and 6.8 months at 8.6 mg/kg—figures that could have real-world impact for late-stage CRC patients.

Safety Profile Remains Favorable with Updated Management Protocols

Among 80 patients receiving doses between 7.2 mg/kg and 10 mg/kg, most side effects were mild to moderate (Grades 1 or 2). Diarrhea was the most frequent treatment-related adverse event (TRAE), but Grade 3 diarrhea was reported in just 10% of those receiving the optimized prophylactic regimen. Serious adverse events were infrequent and generally manageable. Only one Grade 5 event (acute kidney injury) was reported, and it occurred in a patient with a complex medical history at a lower dose.

Key Next Steps: Registrational Study Discussions and Expanded Trials

CytomX intends to engage with the FDA mid-year to align on the design of a potential registrational trial, focusing on the 8.6 mg/kg and 10 mg/kg dosing regimens. In addition, a Phase 1 trial combining Varseta-M with bevacizumab has begun, with a Phase 1b/2 combination study—including chemotherapy—slated for late 2026. Plans are also underway to investigate Varseta-M in other EpCAM-expressing cancers.

Investor Outlook: Data Underscore Advancing Pipeline and Broad Potential

The momentum from these results has added further support to CytomX’s long-term goal of establishing Varseta-M as a new standard for late-line CRC and beyond. With high response and disease control rates, plus proactive safety management, the data could drive heightened interest from both clinical and investment communities as the company moves towards late-stage development and regulatory discussions.

Investors and researchers will find more information on upcoming clinical milestones at CytomX's planned investor call, details of which are available on the company's website. As the company advances towards a registrational trial, the next 12–18 months could prove pivotal for CytomX and colorectal cancer patients alike.

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