In patients with polycythemia vera (PV), the drug Jakafi® (ruxolitinib) can help control disease at least one year. These findings were presented at the 20th Congress of the European Hematology Association in Vienna, Austria, June 11–14, 2015.
Polycythemia vera is a slow-growing type of blood cancer that belongs to a group of blood disorders called myeloproliferative neoplasms (MPN). In these disorders, the bone marrow cells that produce blood cells develop and function abnormally. In PV the bone marrow makes too many blood cells, particularly red blood cells. These excess cells thicken the blood and can cause complications, such as a risk of blood clots or bleeding. Without treatment, PV can be life threatening and can eventually progress to more serious blood cancers, such as myelofibrosis or acute leukemia. Effective treatment, however, can significantly decrease risks and complications.
There is no cure for PV. As a result, treatments that help control symptoms of the disease are incredibly important. Common symptoms include tiredness, itching, muscle aches, night sweats, and sweating while awake. Current standard therapy does not effectively control these symptoms.
Jakafi has proven effective in the therapy of PV, including in patients with intolerance or resistance to standard therapy including Hydrea® (hydroxyurea). Jakafi works by inhibiting proteins (JAK1/JAK2 proteins) that may play a role in the development of MPNs by causing the body to make the wrong number of blood cells. Jakafi may provide better symptom management than Hydrea.
A Phase III study known as the RESPONSE trial has compared the effectiveness of Jakafi with best available therapy in 222 patients with PV who have not responded to or can’t tolerate Hydrea. Of these patients, 110 received Jakafi and 112 received standard therapy. The researchers monitored hematocrit levels among the patients. Hematocrit is a measure of the proportion of total blood volume that is composed of red blood cells; because PV results in excessive levels of red blood cells, hematocrit is used to measure disease control. They also monitored spleen size using imaging (X-ray). Patients assigned to standard treatment were allowed to switch to Jakafi after eight months of treatment.
Early results from RESPONSE were reported 12 months after the last patient started treatment. Based on these findings, patients with PV experience more effective symptom control with Jakafi compared with standard treatment.
A later analysis has evaluated Jakafi for a longer period—20 months after the last patients started treatment. The researchers assessed what they considered a “primary response” to treatment with Jakafi. To qualify as a primary response in each patient, there had to be a reduction in spleen volume of 35% or more at eight months and eight months of hematocrit control without phlebotomy (a procedure to draw blood that is used to manage PV). They also monitored how long each primary response lasted, watched for a return to normal blood cell count (complete hematologic remission), and evaluated the safety of Jakafi.
At the 20-month follow-up, 91 of 110 patients (or 82%) in the Jakafi group were still receiving treatment. None of the patients in the standard therapy group were still on treatment at this time. Of the patients in the Jakafi group, 23 (21%) had met the criteria for a primary response (a 35% or more reduction in spleen volume and hematocrit control). Only one patient in the standard therapy group had a primary response.
The majority of patients receiving Jakafi maintained a long-term response to treatment. At an earlier eight-month follow-up, 60% of patients in the Jakafi group had experienced hematocrit control without phlebotomy compared with just 20% in the standard therapy group. In addition, 38% of Jakafi patients experienced a 35% or greater reduction in spleen volume versus just 1% of standard therapy patients. At this time, 98 patients were still on Jakafi. Between the eight- and 20-month follow-ups, 90% of these patients did not have a phlebotomy. All of the patients in the Jakafi group maintained the spleen volume reduction at eight months. More patients in the Jakafi group had experienced complete hematologic remission at eight months: 24% versus 9%. The researchers estimated that 69% of the Jakafi patients would maintain this remission through 20 months.
Side effects in the Jakafi group tended to be mild to moderate. The most common complaints were headache, diarrhea, itching, and fatigue. A small portion of patients also experienced moderate-to-severe anemia and thrombocytopenia (low platelet count). Only a few patients in the Jakafi group had to stop treatment due to side effects.
Based on these findings, the treatment response to Jakafi in patients with PV appears to last for at least one year. And, in general, patients tolerate the drug well. According to the RESPONSE outcomes, Jakafi continues to prove itself as a promising treatment in PV.
 Kiladjian JJ, Vannucchi AM, Griesshammer M, et al. Ruxolitinib Versus Best Available Therapy in Patients with Polycythemia Vera: 80-Week Follow-Up from the Response Trial. Abstract presented at: 20th Congress of the European Hematology Association (EHA); June 11-14, 2015; Vienna, Austria. Abstract S447.
 Vannucchi AM, Kiladjian JJ, Griesshammer M, et al. Ruxolitinib versus Standard Therapy for the Treatment of Polycythemia Vera. New England Journal of Medicine. 2015 Jan 29;372(5):426-35.
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