REC-4881 Shows 53% Median Reduction in Polyp Burden for FAP: Early Data Points to Durable, Non-Surgical Option

Efficacy Results Indicate Substantial and Lasting Benefit Beyond Treatment

Recursion (NASDAQ: RXRX) has announced promising Phase 1b/2 results for REC-4881, its allosteric MEK1/2 inhibitor developed for familial adenomatous polyposis (FAP)—a hereditary condition that can lead to hundreds of polyps and a near-100% lifetime risk of colorectal cancer. Notably, patients who completed 12 weeks of treatment achieved a median 43% reduction in polyp burden, and an even greater 53% median reduction was sustained at week 25, twelve weeks after treatment ended. The majority (82%) of patients maintained this improvement during the off-therapy period, a critical finding in a disease marked by relentless progression and lack of medical therapy.

Durable Polyp Reduction Persists After Treatment: Unmet Need Addressed

What sets REC-4881 apart from current approaches and other investigational agents is the off-treatment durability—73% of patients sustained reductions of 30% or more in total polyp burden at week 25. This result is even more notable considering natural history studies of FAP: in similar populations, 87% of untreated patients experienced an annualized increase in polyp burden, with a median annual rise of 28%. No existing therapy provides off-treatment durability or addresses the root disease biology.

REC-4881 Provides a Favorable Safety Profile for FAP Patients

The trial included 19 patients across Phase 1b and Phase 2. The majority (94.7%) reported at least one treatment-related adverse event (TRAE), mostly Grade 1 or 2, consistent with known MEK1/2 inhibitors. Grade 3 TRAEs were limited (15.8%), and there were no Grade 4 or higher events. Common TRAEs included rash and increased blood CPK. Importantly, dose interruptions were rare (2 of 19), supporting overall tolerability in this chronic condition.

Clinical Impact: Filling the Gap in FAP Management

FAP, driven by mutations in the APC gene, typically forces patients to undergo invasive surgery as a preventative measure, often in early adulthood, leading to life-long quality-of-life issues. REC-4881 offers the potential for a precision-medicine alternative that could spare patients from frequent major surgeries. The expansion of eligibility down to age 18 further broadens the addressable population—more than 50,000 individuals in the US and EU5—underscoring both clinical and commercial opportunity.

First Clinical Validation for Recursion’s AI Platform: Broader Implications for Drug Discovery

The trial also marks the first clinical validation for the Recursion OS, a proprietary AI-driven drug discovery platform. The ability to identify MEK1/2 inhibition as a strategy for reversing the biology of FAP showcases a powerful technology-driven approach. REC-4881 is the first MEK1/2 inhibitor studied in FAP, opening a potential new class of treatment for genetically driven gastrointestinal diseases.

Next Steps: Toward Regulatory Engagement and Expanded Studies

Looking ahead, Recursion will work with the FDA in the first half of 2026 to define a potential registration pathway and will optimize the dosing schedule in younger patients. The sustained efficacy, tolerability, and platform-driven insights suggest REC-4881 may redefine FAP treatment standards.

Takeaway: A Promising Shift for FAP Care on the Horizon

With REC-4881 demonstrating rapid, meaningful, and lasting reduction in polyp burden—and durability beyond treatment—this first-in-class therapy signals a major advance for FAP patients and a possible proof point for technology-enabled drug discovery. For those tracking clinical innovation in GI diseases and precision medicine, this is one story to follow as it moves into larger and potentially registrational trials.

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