Positive Late-Breaking Data for Incyte's First-in-Class mutCALR-targeted therapy INCA033989 in Essential Thrombocythemia Presented at EHA2025

Incyte (INCY) announced positive Phase 1 clinical data for INCA033989, a novel monoclonal antibody targeting mutant calreticulin (mutCALR) in patients with high-risk essential thrombocythemia (ET). The data, presented at EHA 2025, showed that 86% of patients treated with doses of 400mg and above achieved a complete or partial hematologic response, with 89% of evaluable patients demonstrating a reduction in mutCALR variant allele frequency; the treatment also exhibited a favorable safety profile, potentially transforming the treatment landscape for CALR-mutant myeloproliferative neoplasms (MPNs) with a Phase 3 study planned for early 2026.

Analysis

Incyte's announcement of initial Phase 1 clinical data for INCA033989, a first-in-class monoclonal antibody targeting mutant calreticulin (mutCALR), reveals highly promising results for patients with high-risk essential thrombocythemia (ET). The data, presented at the European Hematology Association 2025 Congress, demonstrated that 86% of patients treated with INCA033989 at doses of 400 mg and above achieved a complete or partial hematologic response, with a substantial 82% achieving complete response. Furthermore, a reduction in peripheral blood mutCALR variant allele frequency (VAF) was observed in 89% of evaluable patients, and 21% achieved a partial molecular response (greater than 50% VAF reduction) after only three treatment cycles, highlighting the drug's potential for disease modification by selectively inhibiting and eliminating oncogenic mutCALR cells while sparing healthy cells and restoring normal blood cell production. Critically, INCA033989 exhibited a favorable safety profile across all dose cohorts (24 to 2,500 mg), with no dose-limiting toxicities reported, a maximum tolerated dose not reached, and 98% of patients remaining on treatment; the most common treatment-emergent adverse events were Grade ≤2 fatigue (26.5%) and upper respiratory tract infection (20.4%). This development is particularly significant as mutCALR is the second most common oncogenic driver in myeloproliferative neoplasms (MPNs), affecting an estimated 60,000 patients with mutCALR positive ET in the U.S. and Europe, a population currently lacking targeted therapeutic options. Incyte plans discussions with regulatory authorities with the goal to initiate a Phase 3 study by early 2026, positioning INCA033989 as a potentially transformative treatment.

Key Decisions for Investors

• The robust Phase 1 efficacy, including an 86% hematologic response rate at doses of 400mg and above and an 89% reduction in mutCALR VAF in evaluable patients, combined with a favorable safety profile for INCA033989, significantly de-risks this first-in-class asset and indicates substantial potential for Incyte.
• Investors should closely monitor upcoming catalysts, particularly the planned initiation of a Phase 3 study by early 2026 and future data presentations, including results for INCA033989 in myelofibrosis, which will be pivotal for realizing the drug's full therapeutic and commercial potential.
• The analyst and investor event held on June 15, 2025, should provide further detailed insights into the INCA033989 program, its competitive positioning, and Incyte's development strategy, influencing near-term market perception.