Momelotinib has a consistent safety profile with no long-term or cumulative toxicity in patients with myelofibrosis, according to a new study published in the journal Blood Advances. This conclusion was reached following the analysis of “one of the largest randomized trial databases for a JAK inhibitor to date in myelofibrosis.”

The analysis used data from 3 phase 3 randomized clinical trials of momelotinib, called MOMENTUM, SIMPLIFY-1, and SIMPLIFY-2 in which a total of 725 patients with myelofibrosis received the treatment.

Read more about the symptoms of myelofibrosis

Of these patients, 12% stayed on momelotinib for at least 5 years. The median treatment exposure for all patients was 11.3 months. 

The study’s authors reported that the most common nonhematologic treatment-emergent adverse event recorded in at least 20% of patients was diarrhea. Hematologic treatment-emergent adverse events included thrombocytopenia, which occurred in 25% of patients, anemia, which occurred in 23% of patients, and neutropenia, which occurred in 7% of patients.

The most common reason to discontinue the treatment, which 4% of patients did, was thrombocytopenia.  

The incidence of adverse events of clinical importance, such as peripheral neuropathy, malignant transformation, infections, or hemorrhage, did not increase with time.

The study authors concluded that these findings suggest a positive risk-benefit balance for momelotinib in patients with myelofibrosis. 

Myelofibrosis is a rare disease characterized by bone marrow scarring caused by the production of excess fibrous tissue. This tissue interferes with the normal production of blood cells and leads to anemia, among other symptoms. Janus kinase (JAK) inhibitors are often used to reduce the production of fibrous tissue in the bone marrow and thereby relieve the symptoms of the disease.

Momelotinib is a JAK1 and JAK2 inhibitor, which was shown to also inhibit activin A receptor type 1, a key regulator of iron homeostasis. The treatment led to improvements in splenomegaly, constitutional symptoms, and anemia in myelofibrosis.


Verstovsek S, Mesa RA, Gupta V, et al. Momelotinib long-term safety and survival in myelofibrosis: integrated analysis of phase 3 randomized-controlled trials. Blood Adv. Published online April 12, 2023. doi:10.1182/bloodadvances.2022009311