SESSION TITLE: Disorders of the Pleura SESSION TYPE: Affiliate Case Report Poster PRESENTED ON: Tuesday, October 31, 2017 at 01:30 PM - 02:30 PM INTRODUCTION: The pleural space is a very rare site of extramedullary hematopoiesis (EMH) in patients with primary myelofibrosis (PMF). Prior reports of pleural EMH suggest poor response to medical treatment with hydroxyurea. In this report, we describe successful treatment of pleural EMH with the JAK2 inhibitor ruxolitinib. CASE PRESENTATION: An 80-year-old woman with a history of PMF, stable for 17 years without treatment, was referred to our pulmonary clinic with 9 months of dry cough, exertional dyspnea and unintentional weight loss. She was breathing at a rate of 16 while resting, with saturation of 94% on ambient air. She had decreased breath sounds on both bases. Imaging revealed moderately sized, bilateral, free flowing pleural effusions. Analysis of the fluid revealed exudative features with abundant megakariocytes and myeloid cells, consistent with EMH. Bilateral pleural effusions with similar symptoms and analytical characteristics recurred after 30 days of treatment with hydroxyurea. Sixty days after changing her treatment to ruxolitinib, she remains symptom free and her pleural effusion has not recurred. DISCUSSION: In the context of PMF, EMH occurs most frequently in the spleen, liver and vertebral bodies. Only 6 cases of EMH involving the pleura have been reported in the past 3 decades. Diagnosis is established by pleural fluid cytology analysis, but pleural biopsy and bone marrow biopsy are also performed for histologic assessment of leukemic infiltration. Although hydroxyurea has been reported to be successful for the treatment of EMH in other sites, previously reported cases of pleural EMH were refractory to treatment with hydroxyurea, and ultimately required pleurodhesis or low dose radiotherapy. Response to treatment with oral JAK2 inhibitors has been seen in patients with myelofibrosis not harboring the JAK2 V617F mutation, suggesting that these agents suppress symptoms through a more general inhibition of the JAK/STAT signaling pathway. There have been no prior reports of use of ruxolitimib for treatment of pleural EMH. CONCLUSIONS: Extramedullary hematopoiesis may occur in the pleural space, causing exudative pleural effusions refractory to standard therapy. To our knowledge, this is the first report of successful use of the JAK2 inhibitor ruxolitinib for treatment of pleural extramedullary hematopoiesis. Reference #1: Koch M, Kurian EM. Pleural fluid extramedullary hematopoiesis case report with review of the literature. Diagn Cytopathol. 2016;44(1):41-44. doi:10.1002/dc.23390. Reference #2: Ghosh AK, Pawade J, Standen GR, Lang-Lazdunski L. Primary extramedullary hematopoiesis manifesting as massive bilateral chylothorax. Ann Thorac Surg. 2005;80(4):1515-1517. doi:10.1016/j.athoracsur.2004.03.088. Reference #3: Ghosh AK, Pawade J, Standen GR, Lang-Lazdunski L. Primary extramedullary hematopoiesis manifesting as massive bilateral chylothorax. Ann Thorac Surg. 2005;80(4):1515-1517. doi:10.1016/j.athoracsur.2004.03.088. DISCLOSURE: The following authors have nothing to disclose: Kenneth Chen, Lirim Krveshi, Guillermo Ballarino No Product/Research Disclosure Information