Ruxolitinib Rechallenge Can Improve Constitutional Symptoms and Splenomegaly in Patients With Myelofibrosis: A Case Series

Myelofibrosis (MF) is one of the classic myeloproliferative neoplasms and can occur de novo or following transformation from polycythemia vera (PPV MF) or essential thrombocythemia (PET MF). It can be associated with constitutional symptoms and splenomegaly, both of which can negatively impact quality of life. The only curative option for MF is allogeneic stem cell transplantation. Studies have shown that JAK2 inhibitors such as ruxolitinib are effective in reducing both splenomegaly and symptom burden. Although there is no approved treatment for patients who progress on ruxolitinib, anecdotal evidence suggests patients may respond to a re-challenge of ruxolitinib after drug cessation.We conducted a multi-institutional, retrospective case series to study patients who were re-challenged with ruxolitinib after inadequate response to or loss of response with an initial treatment course. Thirteen patients were identified. Six patients had primary MF, 3 patients had PPV MF, and 4 patients had PET MF. Ten patients were JAK2-positive, 2 were CALR-positive, and 1 patient had neither mutation. Nine patients received 1 ruxolitinib re-challenge, and 4 received 2 re-challenges. Response was defined as improvement in constitutional symptoms and/or reduction in spleen size.During the primary treatment course with ruxolitinib, there was improvement in constitutional symptoms and reduction in spleen size in 92% and 85% of patients, respectively. Following cessation of ruxolitinib, all patients received a first re-challenge course with improvement in symptoms and splenomegaly in 92% and 69%, respectively. Of the 4 patients who received a second re-challenge course of ruxolitinib, all had improvements in spleen size and constitutional symptoms. Six patients have continued on a first or second ruxolitinib re-challenge course with good response.Our study demonstrates that re-exposure to ruxolitinib following a period of treatment cessation in patients with MF can lead to durable responses with regards to both splenomegaly and symptom burden.