Ruxolitinib is a selective inhibitor of
Janus kinases (JAK) 1 and 2, which are involved in the signalling pathway of various
cytokines and
growth factors essential to haematopoiesis. JAK 1 and 2 are implicated in the development of
myelofibrosis, as well as other haematological
malignancies.
Ruxolitinib is the first agent approved for the treatment of
myelofibrosis. In a randomized, double-blind, placebo-controlled, multicentre trial (COMFORT-I) in patients with
myelofibrosis, significantly more
ruxolitinib than placebo recipients achieved a ≥ 35% reduction in spleen volume (primary endpoint) at 24 weeks. In a randomized, open-label, multicentre trial (COMFORT-II) in patients with
myelofibrosis, significantly more
ruxolitinib than best available
therapy recipients achieved the same primary endpoint at 48 weeks. Significantly more
ruxolitinib than placebo recipients achieved a ≥ 50% reduction in Total Symptom Score at 24 weeks in COMFORT-I.
Ruxolitinib generally improved health-related quality-of-life scores, while best available
therapy was generally associated with worsened scores at 48 weeks in COMFORT-II. In COMFORT-I, overall survival data appeared to favour
ruxolitinib over placebo; of note, most placebo recipients had crossed over to receive
ruxolitinib. In COMFORT-II, a significant difference in overall survival between
ruxolitinib and best available
therapy was not shown; this trial was not powered to detect such a difference. In clinical trials in patients with
myelofibrosis,
ruxolitinib was generally associated with an acceptable tolerability profile. In the placebo-controlled trial, the most commonly reported grade 3 or 4 adverse events in
ruxolitinib recipients were
thrombocytopenia, anaemia and
neutropenia. These haematological adverse events were mainly managed with dosage interruptions/reductions and/or transfusions, and rarely resulted in discontinuation.