A Phase I Study of Ruxolitinib Plus Abemaciclib for Patients With Primary or Post-polycythemia Vera/Essential Thrombocythemia Myelofibrosis

Inclusion Criteria: * Patients with PMF or post-PV/ET MF requiring therapy and intermediate-1, -2 or high risk disease by the Dynamic International Prognostic Scoring System (DIPSS) , DIPSS-plus MIPSS7021 or MIPSS70-plus v2.0 if PMF and by the Myelofibrosis Secondary to PV and ET - Prognostic Model (MYSEC-PM) if post-PV/ET MF * Treated with ruxolitinib for ≥12 weeks with a stable dose for the preceding ≥4 weeks. Patients must be on a dose of ruxolitinib of 10mg or 15mg BID at the time of screening. * Evidence of inadequate response to ruxolitinib: Patients must have palpable splenomegaly ≥5 c…