LCL161 in Treating Patients With Primary Myelofibrosis, Post-Polycythemia Vera Myelofibrosis, or Post-Essential Thrombocytosis Myelofibrosis

Inclusion Criteria: * Patients must provide written informed consent * Willing and able to comply with scheduled visits, treatment plan and laboratory tests * Patient is able to swallow and retain oral medication * Must be diagnosed with treatment requiring PMF or post ET/PV MF with intermediate-1, intermediate -2 or high risk disease according to the International Working Group (IWG) prognostic scoring system, or if with low risk disease then with symptomatic splenomegaly that is \>= 5 cm below left costal margin by physical exam * Patients who are not candidates for, intolerant, or relapsed/refractory to ruxolitinib * Eastern Cooperative Oncology Group (ECOG) performance status 0-2 * Absolute neutrophil count (ANC) \>= 0.5 x 10\^9/L (1500/mm\^3) * Serum direct bilirubin =\< 2.0 x ULN (upper limit of normal) * Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase \[SGOT\]) and alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase \[SGPT\]) =\< 2.5 x ULN, except for patients with MF involvement of the liver who must have AST and ALT =\< 5 x ULN * Serum creatinine =\< 1.5 x ULN * Treatment-related toxicities from prior therapies must have resolved to grade =\< 1 * At least 2 weeks from prior MF-directed treatment (till the start of study drug) Exclusion Criteria: * Any concurrent severe and/or uncontrolled medical conditions that could increase the patient's risk for toxicity while in the study or that could confound discrimination betwee…