Dr. Mascarenhas on the Evolution of JAK Inhibitors in Myelofibrosis

John O. Mascarenhas, MD, professor of medicine, hematology, and medical oncology, Icahn School of Medicine at Mount Sinai, director, the Center of Excellence for Blood Cancers and Myeloid Disorders, member, the Tisch Cancer Institute, discusses evolution of JAK inhibitors in the treatment landscape of myelofibrosis.

For nearly a decade, ruxolitinib (Jakafi) was the only JAK inhibitor approved for the treatment of patients with myelofibrosis after the FDA approved ruxolitinib as the first drug to specifically treat patients with myelofibrosis in November 2011. However, fedratinib (Inrebic) and pacritinib (Vono) joined the treatment paradigm in recent years. In 2019, the FDA approved fedratinib for the treatment of adult patients with intermediate-2 or high-risk primary or secondary myelofibrosis and, most recently, in 2022, the FDA granted an accelerated approval to pacritinib for the treatment of adult patients with intermediate or high-risk primary or secondary (post-polycythemia vera or post-essential thrombocythemia) myelofibrosis with a platelet count below 50 × 109/L. It is anticipated that momelotinib will be approved at some point in 2023, Mascarenhas notes.

Due to the expanding options for JAK inhibitors in the treatment of myelofibrosis, it is critical that practitioners be aware of the different niches that a JAK inhibitor may be applicable, Mascarenhas says.

Because ruxolitinib has been a part of the treatment landscape for nearly a decade and has an established role in the treatment of myelofibrosis, clinicians may be more comfortable with the drug due to a wealth of experience with that particular JAK inhibitor, and it will likely remain the mainstay of JAK inhibitor therapy for patients with myelofibrosis, Mascarenhas continues.

The other JAK inhibitor options can fill needs in specific subsets of patients. Pacritinib represents a treatment option for patients with platelet count of less than 50 x 109/L, and, notably, it can be utilized, irrespective of platelet count, as a second-line JAK inhibitor, Mascarenhas says. Moreover, fedratinib has broader label and can be utilized in the up-front or second-line settings, Mascarenhas says. As a second-line treatment, fedratinib represents a potential option specifically in patients who experience progression or a lack of spleen response with ruxolitinib, Mascarenhas adds. However, neither ruxolitinib nor fedratinib are good drugs for improving anemia and can be associated with myelosuppression, Mascarenhas concludes.