Incyte Corporation announced positive long-term clinical results from an ongoing open-label Phase 2 trial for INCB18424, in patients with advanced polycythemia vera (PV) and essential thrombocythemia (ET). PV and ET, along with myelofibrosis (MF), are blood cancers that belong to a group of diseases known as myeloproliferative neoplasms (MPNs). This trial (Study 18424-256) is an ongoing, multi-center, single-arm, open-label study being conducted in the United States and Italy. An initial 8-week run-in evaluation established 10mg and 25mg twice daily as starting doses for expansion cohorts in PV and ET, respectively.

For PV patients: After a median follow-up of 21 months, 97% of enrolled patients (n=34) achieved hematocrit control to ≤45% in the absence of phlebotomy. All patients continued to maintain phlebotomy-independence at the time of their last follow-up visit. Splenomegaly was present in 74% of patients at entry; 80% of patients achieved a ≥ 50% reduction in palpable spleen length and 68% have achieved complete resolution. Leukocytosis (white blood cell count elevation > 15×109/L) was present in 44% of patients at baseline, and counts normalized in 73%. Thrombocytosis (platelet count elevation > 600×109/L) was present in 38% of subjects at baseline, and counts normalized in 69%. Improvements in patient reported symptoms of pruritus, bone pain, and night sweats have been observed in the majority of patients as of the last follow-up visit.

For ET patients: After a median follow-up of 21 months, 49% of enrolled patients (n=39) normalized platelet counts, and 79% achieved platelet counts < 600×109/L or a ≥ 50% reduction from baseline. Of the 14 patients with extreme thrombocytosis > 1000×109/L at baseline, 13 (93%) experienced > 50% reduction. WBC counts for patients with baseline counts > 10×109/L normalized within the first month and were maintained for a median duration of 14 months. Palpable spleens completely resolved in 3 of 4 patients with baseline splenomegaly; 1 reduced >50% from baseline.

INCB18424 is a JAK1 and JAK2 inhibitor that has shown positive clinical activity in a number of hematology and inflammatory conditions.

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