Ruxolitinib and Lenalidomide As a Combination Therapy for Patients with Myelofibrosis

Background: Ruxolitinib (RUX) is a potent and selective inhibitor of the JAK/STAT pathway that significantly abrogates splenomegaly and constitutional symptoms in patients (pts) with myelofibrosis (MF). Lenalidomide (LEN) is a second-generation immunomodulatory agent that may improve MF-associated anemia and thrombocytopenia. RUX and LEN possess complimentary efficacy profiles.

Aim:Our single-center phase II open-labeled study was conducted to determine the efficacy and safety of the combination of RUX with LEN in pts with MF. Objective improvements were defined using International Working Group for Myelofibrosis Research and Treatment (IWG-MRT) 2007 criteria. We were cognizant of an overlapping toxicity of the two medications, namely myelosuppression.

Methods:Pts received 15 mg RUX orally twice daily in continuous 28-day cycles with 5 mg LEN orally once daily on days 1-21. Dosage was reduced, increased or delayed based on the assessment of efficacy and toxicity.

Results: Thirty-one pts were enrolled between October 2011 and August 2013. Twenty-one (68%) had received prior treatment, including 2 with thalidomide. After a med follow-up of 21.6 mo (1.9-27.7), 28 pts remain alive. The median time on study was 14.7 mo (1.8-26.6) and the median number of cycles administered was 15 (1-29).

Simultaneous administration of RUX and LEN was difficult. Only 2 (6%) pts have not required a dose interruption/dose adjustment. The median time to first dose interruption/dose adjustment was 56 days (4-360). Among the 29 pts who needed a dose interruption/adjustment, 23 (79%) needed it within 3 months of starting therapy. The first change in 23 (74%) pts was a dose interruption: median time to first dose interruption was 56 days (4-360), with 20 (87%) of the dose interruptions occurring within 3 months of therapy. LEN was held in all 23 pts and 14 (61%) never restarted LEN. RUX was concurrently held in 7 (30%), reduced in 9 (40%), and continued at same dose in 7 (30%). Reasons for the first dose interruption were low platelets (n=8), low absolute neutrophil count (n=3), anemia (n=3), diarrhea (n=3), financial constraints (n=2), deep vein thrombosis (n=1), skin rash (n=1), transaminitis (n=1), and arthralgia/fever (n=1). The first change in 6 (19%) pts was a dose increase (all in RUX): median time to dose increase was 83 days, with 3 (50%) of the increases occurring within 3 months of starting therapy. The reasons for dose increase were leukocytosis (n=2), suboptimal response (n=2), increased spleen size (n=1), and thrombocytosis (n=1). At the time of submission, 18 pts remain on study: 7 on RUX alone and 11 on both medications.

IWG-MRT defined clinical improvement (CI) in splenomegaly was noted in 11 (36%) pts. Of note, CI in splenomegaly was seen in 6 of 11 (55%) pts who did not require a dose interruption in the first 3 months. Median time to response was 1.0 mo (0.4-9.1) and median response duration was 19.3 mo (9.4-25.6+). An additional 18 (58%) pts had IWG-MRT defined stable disease. Reasons for discontinuation in 13 pts were lack of response (n=2), infection (n=2), progression (n=1), neuropathy (n=1), renal failure (n=1), diarrhea (n=1), myelosuppression (n=2), concurrent lymphoma (n=1), and financial constraints (n=2). Grade 3/4 myelosuppression was noted in 13 pts. Five pts experienced grade 3/4 non-hematological toxicity (related and unrelated): G3 diarrhea (n=1), G3 edema (n=1), G4 acute kidney injury (n=1), and G3 liver enzyme (n=2).

Conclusion: Concomitant administration of RUX with LEN resulted in early dose interruption in a majority of pts. Most pts were unable to restart LEN after dose interruption. Starting the two drugs simultaneously compromised the expected efficacy of RUX alone. A sequential approach with single-agent RUX for the first 3-6 months followed by the addition of the second agent once a steady dose of RUX has been achieved and optimal benefit reached may be a more viable approach for future RUX combination strategies.