ATLANTA—A new study suggests the JAK2 inhibitor ruxolitinib has the potential to significantly improve survival in patients who have chronic phase (CP) myelofibrosis (MF), with or without elevated blasts.

In this retrospective study, researchers found evidence to suggest that MF patients in CP with elevated blasts (CP-e) should be considered a high-risk group.

However, ruxolitinib significantly improved overall survival (OS) in CP-e patients—who had 5% to 9% blasts in the bone marrow or peripheral blood—and in patients with CP and less than 5% blasts.

On the other hand, ruxolitinib had no impact on the rate of progression to acute myeloid leukemia (AML) in CP or CP-e patients.

Lucia Masarova, MD, of The University of Texas MD Anderson Cancer Center in Houston, presented these findings at the 2017 ASH Annual Meeting (abstract 201).

Clinical characteristics of MF CP-e patients are not well described, and the outcome of available therapy in this population is largely unknown. Therefore, Dr Masarova and her colleagues set out to evaluate the effects of ruxolitinib on CP-e patients.

The team conducted a retrospective chart review of 1199 MF patients, 832 with primary MF, 169 with post-essential thrombocythemia MF, and 198 with post-polycythemia vera MF. About two-thirds of the patients were newly diagnosed.

The majority of patients (85%, n=1020) were in CP with less than 5% blasts, 10% (n=123) were in CP-e, and 5% (n=56) were in accelerated phase (AP, 10% to 19% blasts).

CP-e patients had similar clinical characteristics as patients in AP. Both groups had higher white blood cell counts; lower hemoglobin and platelets; and more frequent splenomegaly, systemic symptoms, and presence of abnormal and unfavorable karyotype than CP patients.

Among the 1030 treated patients, ruxolitinib was used in 30% (n=328), including 28% of CP patients (n=289), 27% of CP-e patients (n=33), and 11% of AP patients (n=6). The median treatment duration was about 22 months in the CP and CP-e groups.

After a median follow-up of 27 months, half the patients studied had died.

“Patients in the [CP-e] group had similar OS as those in AP, which was inferior to patients in CP,” Dr Masarova said.

The median OS was 48 months for the entire cohort, 56 months in the CP group, 34 months in the CP-e group, and 23 months in the AP group.

One-year OS rates were 86% for the CP group, 73% for the CP-e group, and 65% for the AP group. Five-year OS rates were 46%, 24%, and 21%, respectively.

CP and CP-e patients had superior OS if they had received ruxolitinib.

Among CP patients, the median OS was 61 months in those who received ruxolitinib and 54 months in those who did not (hazard ratio=0.85, P=0.002).

Among CP-e patients, the median OS was 54 months in those who received ruxolitinib and 27 months in those who did not (hazard ratio=0.50, P=0.001).

Ruxolitinib had no impact on OS in AP patients, which was 23 months with or without the drug. However, Dr Masarova noted that the AP patient numbers were small.

Progression to AML occurred in 9% of patients overall (n=139), 9% in the CP group, 20% in the CP-e group, and 39% in the AP group.

Ruxolitinib had no impact on the rate of AML progression, which was 9% in CP patients, with and without the drug.

In CP-e patients, AML progression occurred in 22% of those who received ruxolitinib and 18% of those who did not.

“The [CP-e] patients are similar to AP patients, with adverse clinical characteristics, inferior OS, and a 20% to 40% AML rate,” Dr Masarova said. “Ruxolitinib improves survival of [CP-e] patients, which is similar to CP patients on the drug.”

CP-e patients should be considered a high-risk population, she said, adding “we need to find new, better treatments for these patients.”

Dr Masarova had no disclosures.

Ruxolitinib improves survival for MF patients in CP-e