For patients with polycythemia vera without splenomegaly who had inadequate responses to hydroxyurea, targeted therapy with the Janus kinase (JAK) inhibitor ruxolitinib (Jakafi) offered better control of hematocrit and better improvement of symptoms than did the best available therapy, according to results of a multinational randomized phase IIIb trial.
Among 74 patients randomly assigned to receive ruxolitinib, 46 (62%) achieved hematocrit control, compared with 14 of 75 patients (19%) assigned to receive one of several different options lumped into the best available therapy category, noted investigators led by Francesco Passamonti, MD, of the University of Insubria in Varese, Italy.
“Ruxolitinib also led to an improved symptom burden and quality of life. Patients treated with ruxolitinib experienced improvements in all polycythemia vera–associated symptoms, including pruritus, whereas patients treated with best available therapy experienced worsening of most symptoms,” they wrote.
Unlike cytoreductive therapies such as hydroxyurea or pegylated interferon, ruxolitinib works by inhibition of JAK1 and JAK2 signaling. A majority of patients with polycythemia vera have an activating JAK2 mutation that leads to overactivation of the JAK-STAT signaling pathway, resulting in erythrocytosis, the hallmark symptom of polycythemia vera, and associated vascular complications.
“In some patients, conventional therapies can lose effectiveness over time. Although hydroxyurea is well tolerated in most patients, about 15%-20% of patients become resistant or intolerant, with hydroxyurea resistance affecting survival and increasing the risk of progression to myelofibrosis. Additionally, patients who are intolerant of hydroxyurea can have adverse side effects, such as drug-induced fever, mouth ulcers, leg ulcers, and skin malignancies, which necessitate discontinuation of first-line therapy,” the investigators noted.
RESPONSE trials
Ruxolitinib had previously been shown in the RESPONSE study to be superior to the best available therapy for controlling hematocrit and for improving splenomegaly and other symptoms in patients with polycythemia vera and disease-associated splenomegaly who had an inadequate response or unacceptable toxicities from treatment with hydroxyurea.
In the currently reported study, dubbed RESPONSE-2, patients 18 and older with polycythemia vera with no palpable splenomegaly who were intolerant of hydroxyurea or had disease that was resistant to it were randomized to receive either oral ruxolitinib 10 mg twice daily, or best available therapy at the investigators’ discretion. Best available therapy consisted of either hydroxyurea at the maximum tolerated dose, interferon or pegylated interferon, pipobroman, anagrelide, approved immunomodulators, or no cytoreductive treatment.
As noted, hematocrit control at week 28, the primary endpoint, was significantly higher among patients on ruxolitinib, with an odds ratio (OR) of 7.28 (P less than .0001).
Hematocrit levels among patients on ruxolitinib group decreased from a mean of 42.8% at baseline to 40.2% at week 28. In contrast, hematocrit in the best available therapy group increased from a mean of 42.7% to 44.9% at week 28.
Fewer patients on ruxolitinib required phlebotomy procedures during the 28 weeks of the study compared with patients on best available therapy, and of those patients who did undergo phlebotomy, fewer of those in the ruxolitinib group underwent more than two procedures. There were a total of 98 phlebotomies among best available care patients, vs. 19 among ruxolitinib patients.
Complete hematologic remissions, a secondary endpoint, occurred in 23% of patients on ruxolitinib, compared with 5% of those on best available care (OR 5.58, P = .0019).
The most frequent hematologic adverse events of any grade were anemia, which occurred in 10 patients on ruxolitinib (none grade 3 or greater) vs. two on best available therapy (one grade 3), and thrombocytopenia occurring in two (both grade 1 or 2) and six patients (three grade 1 or 2, two grade 3, and one grade 4) respectively.
Grade 3 or 4 nonhematologic adverse events included hypertension in five patients on ruxolitinib vs. three on best available care, and pruritus in none vs. two, respectively.
Two patients died; both were in the best available therapy group.
“Although the short follow-up of this study precludes any conclusions about vascular complications, an important finding is that patients treated with ruxolitinib in both RESPONSE and RESPONSE-2 had fewer thromboembolic events compared with those given best available therapy; there were two thromboembolic events with ruxolitinib (one in each study) versus nine with best available therapy across both studies (six in RESPONSE and three in RESPONSE-2). This finding could have been attributable to better control of hematocrit or white blood cell count with ruxolitinib, given that baseline risk factors were similar in both treatment groups,” the investigators wrote.
The findings from the two studies support the use of ruxolitinib as a standard of care for second-line therapy of patients with polycythemia vera following treatment with hydroxyurea, they contended.
Several coauthors disclosed ties to Novartis, which supported the study. Two are Novartis employees; one was previously employed by the company.