Ruxolitinib, an orally bioavailable and selective inhibitor of
Janus kinase 1 (JAK1) and JAK2, significantly reduces
splenomegaly and disease-related symptoms in patients with
myelofibrosis (MF). However, no clear survival benefit has been demonstrated, which may in part reflect suboptimal
drug exposure related to lower dosages needed to minimize hematological toxicity, specifically
cytopenias. Furthermore, the optimal management of specific conditions such as
leukocytosis or
thrombocytosis in patients under
ruxolitinib therapy is still undefined. In these cases, combining
ruxolitinib with a cytoreductive agent like
hydroxyurea might improve hematological response. This observational multi-center study enrolled 20 adult patients with intermediate- or high-risk primary MF, post-
polycythemia vera MF, or postessential
thrombocythemia MF with hyperproliferative manifestations of the disease and WBC and/or platelet counts not controlled by
ruxolitinib therapy. The patients received treatment with a combination of
ruxolitinib and
hydroxyurea. A clinical response of any type was obtained in 8 patients (40%) during
ruxolitinib monotherapy and in 17 patients (85%) during
ruxolitinib-
hydroxyurea combination (P = 0.003). After a median duration of 12.4 months of combination
therapy, 16/20 patients had a hematological response; 14/17 patients who had started combination
therapy to control WBC count and 2/3 who started in order to reduce platelets count. The number of patients requiring
ruxolitinib dosage reduction or discontinuations was lower during combination
therapy and, at the end of follow-up the median
ruxolitinib dose was increased in 50% of patients. In conclusion, the combination of
hydroxyurea with
ruxolitinib yielded a high clinical response rate and increased
ruxolitinib exposure in patients with hyperproliferative forms of MF.