Therapy of myelofibrosis (excluding JAK2 inhibitors)

Advances in the management of myelofibrosis

BACKGROUND

Myelofibrosis (MF) is a rare and serious hematologic malignancy classified as a Philadelphia chromosome-negative myeloproliferative neoplasm (MPN). The disease is more common in males and in older individuals. Of the MPNs, MF presents with the most severe morbidity and greatest mortality. Although the cause of MF is unknown, it is thought to occur from acquired mutations that target the hematopoietic stem cell.

METHODS

We reviewed the current literature pertaining to the pathophysiology, clinical presentation, diagnosis, risk stratification, and treatment of MF. The strengths and limitations of present treatment options as well as the emerging clinical experience with Janus kinase 2 (JAK2) inhibitors are explored.

RESULTS

Diagnosis is often one of exclusion and is facilitated using the World Health Organization or International Working Group for Myelofibrosis Research and Treatment criteria, depending on whether primary or secondary MF is suspected. Treatment is complicated by a lack of disease familiarity of general practitioners and the advanced age of presenting patients. Although allogeneic stem cell transplant offers a potential cure, most treatments for this condition are limited to symptomatic management, with little to no effect on survival. Appropriate patient assessment and risk stratification are essential for predicting outcomes and allowing treating physicians to tailor therapy accordingly.

CONCLUSIONS

Significant advances have been made in understanding the pathophysiology of MF, leading to novel therapeutic approaches. The discovery of the JAK2 mutation and the development of JAK2 inhibitors provide clinicians with a new effective treatment option. Ruxolitinib is the first JAK1/2 inhibitor approved by the Food and Drug Administration (FDA) for the treatment of patients with intermediate- or high-risk MF. In clinical studies, ruxolitinib produced a significantly greater reduction in spleen size and improved quality of life compared with placebo or best available therapy. Several future therapies, including combination therapies with ruxolitinib, are currently under investigation.

Ruxolitinib: a new JAK1/2 inhibitor that offers promising options for treatment of myelofibrosis

Ruxolitinib (INCB018424) is the first potent, selective, oral inhibitor of JAK1 and 2 being developed for clinical use. Its major cellular and systemic effects are proliferation inhibition, apoptosis induction and reduction in cytokine plasma levels, all mediated by the drug's inhibition of JAKs' ability to phosphorylate STAT. In initial clinical trials of its use in myelofibrosis, ruxolitinib exhibited durable efficacy in reduction of splenomegaly and alleviation of constitutional symptoms. Patients also showed weight gain and improvement in general physical condition. The dose-limiting toxicity was thrombocytopenia. In preliminary findings of a Phase III trial in patients with primary, postpolycythemia-vera, or postessential-thrombocythemia myelofibrosis, administration at an initial dosage of 15 or 20 mg twice daily led to a spleen-volume response rate (≥ 35% reduction at 24 weeks) of 41.9 versus 0.7% for placebo (p < 0.0001); furthermore, 45.9% of the ruxolitinib recipients had ≥ 50% improvement in symptom score (on the modified Myelofibrosis Symptom Assessment Form version 2.0) versus 5.3% for placebo (p < 0.0001). Ruxolitinib recipients also showed improvement in parameters of quality of life.

Myelofibrosis successfully treated with prednisolone in a patient with pachydermoperiostosis

Pachydermoperiostosis (PDP) is a rare disorder of bone and connective tissue growth. A 21-year-old man was referred to our hospital with anemia. He showed characteristics of PDP. Bone marrow biopsy showed myelofibrosis. Chromosomal abnormalities or JAK2 mutation were not found. Anemia gradually progressed, and he became transfusion-dependent. Oral prednisolone was initiated; it gradually improved his anemia and rendered the patient free of transfusion. However, other clinical symptoms such as clubbed fingers and skin hypertrophy remained unimproved. In this case, the serum concentration of vascular endothelial growth factor and transforming growth factor-β levels were increased. Further investigation will be necessary to establish appropriate treatment strategies for this disease.