Phase II, Open Label, Single Arm Study of SAR302503 In Myelofibrosis Patients Previously Treated With Ruxolitinib

Primary Objective: \- To evaluate the efficacy of once daily dose of SAR302503 in subjects previously treated with ruxolitinib and with a current diagnosis of intermediate-1 with symptoms, Intermediate-2 or high-risk primary myelofibrosis (PMF), post-polycythemia vera myelofibrosis (Post-PV MF), or post-essential thrombocythemia myelofibrosis (Post-ET MF) based on the reduction of spleen volume at the end of 6 treatment cycles; Secondary Objectives: * To evaluate the effect of SAR302503 on Myelofibrosis (MF) associated symptoms as measured by the modified Myelofibrosis Symptom Assessment Form (MFSAF) diary * To evaluate the durability of splenic response * To evaluate the splenic response to SAR302503 by palpation at the end of Cycle 6 * To evaluate the splenic response to SAR302503 at the end of Cycle 3 * To evaluate the effect of SAR302503 on the Janus kinase 2 (JAK2) V617F allele burden * To evaluate the safety and tolerability of SAR302503 in this population * To evaluate plasma concentrations of SAR302503 for population PK analysis, if warranted