WILMINGTON, DE — Incyte (Nasdaq: INCY) reported strong early-stage clinical results for an experimental precision antibody that sharply reduced disease markers in patients with essential thrombocythemia, bolstering hopes for a targeted treatment in a condition with limited options.
Updated data from two Phase 1 studies showed that nearly 90 percent of patients treated with higher doses of INCA033989 achieved a hematologic response, with more than 83 percent reaching a complete response marked by normalized platelet and white blood cell counts. The findings were presented in oral sessions at the American Society of Hematology’s 2025 annual meeting.
INCA033989 is a first-in-class monoclonal antibody designed to target mutant calreticulin, a genetic driver found in roughly one-quarter to one-third of essential thrombocythemia cases. Patients with this mutation often face aggressive disease and limited benefit from existing therapies, which broadly suppress blood cell production rather than directly addressing the underlying mutation.
Beyond blood count improvements, Incyte reported rapid and durable molecular responses. Nearly all patients with follow-up measurements showed reductions in mutant CALR variant allele frequency, a key indicator of disease burden. About half achieved reductions of at least 25 percent, while nearly one-third saw reductions of 50 percent or more. Deeper and more consistent responses were observed at higher doses.
Exploratory analyses suggested the drug may directly alter disease biology. Researchers observed reductions in mutant stem and progenitor cells and improvements in abnormal bone marrow cell growth, findings that point toward potential disease-modifying activity rather than symptom control alone.
Safety data were also encouraging. No dose-limiting toxicities were reported, and a maximum tolerated dose was not reached. Most adverse events were mild to moderate, with fatigue, headache, upper respiratory infections, and anemia among the most common. Only one patient discontinued treatment due to side effects.
The U.S. Food and Drug Administration has granted Breakthrough Therapy designation to INCA033989 for patients with Type 1 CALR-mutated essential thrombocythemia who are resistant or intolerant to prior cytoreductive therapy, a move that could speed future development and review.
Incyte said it plans to advance the drug into a registrational program covering both Type 1 and non-Type 1 CALR mutations, positioning INCA033989 as a potential shift toward mutation-specific treatment in myeloproliferative neoplasms.
For investors, the results strengthen Incyte’s pipeline narrative by highlighting a novel, targeted approach with early signs of durable efficacy and manageable risk, an increasingly prized combination in oncology and rare disease drug development.
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