Image courtesy of AFIP
VIENNA—Updated results from the phase 3 RESPONSE trial suggest the JAK1/2 inhibitor ruxolitinib can provide long-term disease control in patients with polycythemia vera (PV) who are resistant to or intolerant of hydroxyurea.
At 18 months of follow-up, 80% of patients had achieved a durable response to ruxolitinib, sustaining hematocrit levels below 45% without the use of phlebotomy and experiencing reductions in spleen size.
In addition, 83% of patients were still receiving ruxolitinib at last follow-up.
“Polycythemia vera can lead to serious complications if inadequately controlled, and these data demonstrate the ability of [ruxolitinib] to provide a durable and comprehensive clinical benefit in this patient population,” said Jean-Jacques Kiladjian, MD, PhD, of Hôpital Saint-Louis et Université Paris Diderot in France.
Dr Kiladjian presented these results at the 20th Congress of the European Hematology Association (abstract S447). The RESPONSE trial was sponsored by Incyte Corporation and Novartis Pharmaceuticals, the companies developing ruxolitinib.
The study included 222 patients with PV whose were resistant to or could not tolerate hydroxyurea. They were randomized 1:1 to receive either ruxolitinib (at a starting dose of 10 mg twice daily) or best available therapy (BAT), which was defined as investigator-selected monotherapy or observation only. The ruxolitinib dose was adjusted as needed throughout the trial.
The study’s primary endpoint was the proportion of patients who achieved hematocrit control and were not eligible for phlebotomy from week 8 through 32 (with no more than 1 instance of phlebotomy eligibility between randomization and week 8) and who saw a 35% or greater reduction in spleen volume from baseline, as assessed by imaging at week 32.
Patients were deemed eligible for phlebotomy if they had hematocrit that was greater than 45% and had increased 3 or more percentage points from the time they entered the trial or if they had hematocrit greater than 48%.
The researchers performed a second, preplanned analysis at 80 weeks (18 months), evaluating the durability of primary response, hematocrit control, spleen size reduction, complete hematologic remission, and safety. The team also conducted a separate analysis evaluating hematologic parameters.
Results at 32 and 80 weeks
Twenty-one percent of patients in the ruxolitinib arm and 1% of patients in the BAT arm achieved the primary endpoint (P<0.0001). All but 1 of the responders in the ruxolitinib arm maintained this response at 80 weeks.
Sixty percent of patients in the ruxolitinib arm and 20% in the BAT arm achieved hematocrit control without phlebotomy through week 32. Patients in the ruxolitinib arm had an 89% probability of maintaining this response for 80 weeks from the time of initial response. Of the 98 patients on ruxolitinib at week 32, 90% did not have a phlebotomy between weeks 32 and 80.
At week 32, 38% of patients in the ruxolitinib arm and 1% of patients in the BAT arm achieved a 35% or greater reduction in spleen volume. All of the ruxolitinib-treated patients maintained this response at 80 weeks.
At week 32, 24% of patients in the ruxolitinib arm had a complete hematologic remission, as did 9% of patients in the BAT arm. Patients in the ruxolitinib arm had a 69% probability of maintaining this response for 80 weeks.
A separate analysis of the data at 18 months demonstrated that ruxolitinib treatment also led to sustained control of white blood cell and platelet levels, with the largest reductions occurring in patients who had the most elevated values at baseline.
At week 80, 83% of patients in the ruxolitinib arm remained on treatment (median exposure of 111 weeks), but none of the patients in the BAT arm were still receiving their assigned therapy.
At 80 weeks, the most common adverse events in the ruxolitinib arm were headache (22%), diarrhea (20%), pruritus (20%), and fatigue (17%). Grade 3 or 4 anemia and thrombocytopenia occurred in 2% and 6% of patients, respectively. Five percent of patients discontinued treatment due to adverse events.
“There is currently a significant unmet need for patients with polycythemia vera who are unable to tolerate or control their disease on other treatments,” Dr Kiladjian said. “For these patients, [ruxolitinib] represents a valuable new option, as confirmed by results from the long-term, phase 3 study.”
