Real-World Study Backs Long-term Use of Ruxolitinib in Myelofibrosis

New study findings are bolstering results of the JAK Inhibitor Ruxolitinib in Myelofibrosis Patients (JUMP) and COMFORT studies, demonstrating that ruxolitinib is a safe treatment for patients with myelofibrosis (MF). According to the researchers, the results support long-term treatment with ruxolitinib, the only approved treatment for the rare disease.

Just last week, primary analysis results from the phase 3 JUMP study were published, showing that the drug reduced spleen length by at least 50% in more than half of patients with splenomegaly and reduced symptoms of patients with MF.

The present real-world, observational study, which looked at long-term outcomes among patients from the JUMP trial and the Individual Patient Supply Program, was conducted as part of an agreement with the European Medicines Agency to offer post-marketing exposure data.

Among the 462 patients, the most commonly reported adverse drug reactions were thrombocytopenia, anemia, epistaxis, urinary tract infection, and herpes zoster. This was consistent across all patients, which included prevalent users (n = 260) and new users (n = 32), as well as 170 patients who were not exposed to ruxolitinib. All patients were followed for approximately 3 years.

These findings are similar to those of the pivotal COMFORT studies, which ruxolitinib’s approval was based on, as well as other studies, which also found that anemia and thrombocytopenia were the most common hematological adverse drug reactions reported.

“As JAK2 has an essential function in mediating signals from erythropoietin and thrombopoietin, some degree of reversible myelosuppression is an expected consequence of KAJ inhibition, leading to dose-dependent anaemia and thrombocytopenia,” explained the researchers.

When calculating the exposure-adjusted incidence rates (per 100 patient-years) of thrombocytopenia and anemia in the current study, the incidence rates were highest among the ruxolitinib-switch patients (10.8 and 10.8, respectively)—a subset of patients in the non-exposed cohort that were exposed to ruxolitinib during the study—followed by new users (5.9 and 8.9, respectively) and prevalent users (5.3 and 3.8, respectively).

According to the researchers, higher incidence rates among ruxolitinib-switch patients could be a result of shorter duration of exposure to the drug (20.3 months) compared with prevalent users (33.4 months) and new users (26.1 months).

“The apparent variations in the incidence rate/frequency of AEs between different cohorts were due to differences in exposure to ruxolitinib and consecutively a more advanced disease in the switch cohort,” explained the researchers, who noted that these ruxolitinib-switch patients mostly experienced disease progression before the switch.

Looking at the exposure-adjusted incidence rates for all adverse drug reactions, the researchers found that incidence rates were again notably higher among ruxolitinib-switch patients (33.4) and were similar between prevalent and new users (19.6 and 19.3, respectively).

Anemia was also one of the most frequently reported serious adverse events, in addition to pneumonia, general physical health deterioration, sepsis, and death. Incidence rates were slightly higher among the ruxolitinib-switch cohort (29.1) compared with prevalent users (25.0) and new users (25.2).

Similarly, incidence rates of bleeding events (21.6) and serious/opportunistic infections (34.5) were higher among the ruxolitinib-switch patients than other patients.

As they expected, the researchers found less events of special interest among patients not exposed to ruxolitinib, who had a low-risk MF compared with the other patients.

Notably, ruxolitinib did not appear to have an impact on other malignancies, according to the researchers; they found that history of malignancies and prior exposure to hydroxyurea were the most associated with an increased risk of developing other solid tumors, with the exception of non-melanoma skin cancers.

Reference

Barraco F, Greil R, Herbrecht R, et al. Real-world non-interventional long-term post-authorisation safety study of ruxolitinib in myelofibrosis. Br J Haematol. Published online June 24, 2020. doi: 10.1111/bjh.16729.