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Positive Results Reported From Pivotal Phase III Trial of Ruxolitinib (Jakafi) in Polycythemia Vera

Study meets primary composite endpoint of hematocrit control and reduced spleen volume

Positive results have been reported from the RESPONSE trial, the first pivotal phase III study evaluating a Janus kinase 1 (JAK1) and JAK2 inhibitor for the treatment of polycythemia vera (PV).

Ruxolitinib (Jakafi, Incyte Corporation), compared with best available therapy (BAT), significantly improved hematocrit control (red blood cell volume) without the need for phlebotomy and reduced spleen size in patients with uncontrolled PV (i.e., those who were resistant to or intolerant of hydroxyurea [HU]).

Findings from this study were presented at the 50th annual meeting of the American Society of Clinical Oncology, held May 30–June 3 in Chicago.

Seventy-seven percent of ruxolitinib-treated patients compared with 20% of BAT-treated patients achieved at least one component of the primary endpoint: hematocrit control from week 8 to week 32 and/or at least a 35% reduction in spleen volume. A significantly greater proportion of patients treated with ruxolitinib achieved the composite primary endpoint compared with the BAT group (21% vs. 1%, respectively; P < 0.0001); 91% of patients in the ruxolitinib group who achieved this endpoint maintained their response at week 48.

A greater proportion of patients in the ruxolitinib treatment arm had complete hematologic remission, a key secondary endpoint, compared with the BAT arm (24% vs. 9%, respectively; P = 0.003). Patients treated with ruxolitinib also experienced meaningful improvements in PV-related symptoms; 49% of the ruxolitinib group compared with 5% of the BAT group showed a 50% or greater improvement in symptom scores at week 32, as measured by the 14-item Myeloproliferative Neoplasm Symptom Assessment Form (MPN-SAF). At week 32, one patient in the ruxolitinib group and six patients in the BAT group experienced a thromboembolic event.

The RESPONSE trial was an open-label randomized study of 222 patients with PV conducted in North America, Europe, Asia, and Australia. Patients with splenomegaly who were resistant to or intolerant of HU and required phlebotomy were randomly assigned to receive ruxolitinib 10 mg twice daily or BAT, which was defined as investigator-selected monotherapy or observation only. From week 32, patients in the BAT group could cross over to receive ruxolitinib therapy. The study’s primary endpoint was the proportion of patients who achieved both hematocrit control without the need for phlebotomy from week 8 through week 32 and a spleen volume reduction of at least 35% from baseline at week 32.

PV is a myeloproliferative neoplasm (MPN) characterized by an overproduction of normal red blood cells, white blood cells, and platelets, which leads to an increased risk of thrombosis. Erythrocytosis is the most prominent clinical manifestation of PV, distinguishing it from other MPNs. PV may occur at any age but often presents later in life, with a median age of 60 years at diagnosis. Approximately 100,000 individuals in the U.S. have PV, and approximately 25% of patients with the disorder develop resistance to or intolerance of HU and are considered uncontrolled.

The most common signs and symptoms of PV are fatigue, pruritus, night sweats, bone pain, fever, and weight loss. Splenomegaly is present in 30% to 40% of patients with PV.

Jakafi (ruxolitinib) is a prescription medicine approved by the FDA to treat patients with intermediate or high-risk myelofibrosis (MF), including primary MF, post–polycythemia vera MF, and post–essential thrombocythemia MF.

Source: Incyte Corporation; June 3, 2014.

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