Exploratory analysis of the effect of ruxolitinib on bone marrow morphology in patients with myelofibrosis.

Abstract

7030 Background: Myelofibrosis(MF) is characterized by splenomegaly, burdensome symptoms, progressive bone marrow (BM) fibrosis, and shortened survival. Ruxolitinib (Rux), an oral, FDA-approved JAK1/JAK2 inhibitor, has demonstrated improvements in spleen volume, symptoms, and survival in patients (pts) with MF. This study was conducted to explore possible effects of long-term Rux treatment on BM morphology in MF. Methods: Trephine biopsies were obtained at baseline, 24 (67 pts), and 48 (17 pts) months (mo) from the cohort of MF patients treated at MD Anderson Cancer Center who participated in a phase I/II trial of Rux (NCT00509899). The clinical outcomes from this trial have been published previously [Verstovsek, NEJM 2010]. Two of the authors (JT and HMK) independently evaluated the World Health Organization (WHO)-defined BM fibrosis grade (0-3). Reviewers were blinded to pts characteristics and outcomes and consensus decided discordant scores. For demonstrative purposes, WHO BM fibrosis grading was also determined for a control cohort of pts treated with hydroxyurea (HU) for 24 (31 pts) and 48 (20 pts) mo. Changes in BM fibrosis grade vs. baseline were calculated for 24 and 48 mo, and categorized as improvement, stabilization, and worsening for each patient. Results: A higher percentage of Rux-treated pts showed stabilization or improvement of BM fibrosis at both 24 and 48 mo than the HU-treated pts. Worsening was greater in the HU-treated cohort at both time points. Conclusions: This exploratory analysis of long-term exposure to Rux in MF provides the first indication that JAK inhibitor therapy may be able to meaningfully retard advancement of BM fibrosis. A comparable effect was not seen with long-term HU therapy. Additional research is needed to further elucidate these findings. Clinical trial information: NCT00509899. [Table: see text]