Nivolumab in Treating Patients With Primary Myelofibrosis, Post-Essential Thrombocythemia Myelofibrosis, or Post-Polycythemia Vera Myelofibrosis

PRIMARY OBJECTIVES: I. To determine the efficacy/clinical activity of nivolumab in patients with myelofibrosis (MF). SECONDARY OBJECTIVES: I. To determine the safety of nivolumab in patients with MF. TERTIARY OBJECTIVES: I. To explore time to response and duration of response. II. To assess changes in symptom burden. III. To explore changes in bone marrow fibrosis. IV. To explore changes in Janus kinase 2 valine at amino acid position 617 (JAK2V617F) (or other molecular marker) allele burden or changes in cytogenetic abnormalities. OUTLINE: Patients receive nivolumab intravenously (IV) over 60 minutes once every 2 weeks for 8 doses and then once every 12 weeks thereafter. Treatment may continue for up to 4 years in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up at 30, 60, and 100 days.