SESSION TITLE: Pulmonary Manifestations of Systemic Disease 1 SESSION TYPE: Affiliate Case Report Poster PRESENTED ON: Tuesday, October 31, 2017 at 01:30 PM - 02:30 PM INTRODUCTION: Acute Myeloid Leukemia (AML) patients often present with respiratory symptoms and non-specific radiological findings. Extramedullary infitration (EMI) of soft tissues is a rarer form of presentation. CASE PRESENTATION: A 74-yo-white male farmer, ex-smoker, with a history of hypertension, hyperlipidemia and coronary artery bypass grafting presented with symptoms of weakness, shortness of breath on exertion and fatigue for 3 weeks. He did not report any chills, night sweats or fevers during this time. On examination, his vital signs were stable and he had bibasilar crackles on auscultation of his lungs. His WBC count was elevated at 38,700/mcL (predominantly monocytes 46%) with 12% blasts, hemoglobin level was 7.4 g/dL and platelet count 43,000/mcL. CT chest showed prominent mediastinal lymphadenopathy, involving the right paratracheal and subcarinal lymph nodes. A bone marrow aspirate showed 26% myeloid blasts with monocytic differentiation confirming the diagnosis of Acute Myeloid Leukemia (AML). The mediastinal lymphadenopathy persisted despite antibiotics and Decitabine chemotherapy. Bronchoscopy and transbronchial needle aspiration of the subcarinal lymph node confirmed the presence of myeloid blasts in the subcarinal lymph nodes. DISCUSSION: EMI occurs more commonly in the myelo-monoblastic subtypes of AML. Myeloid sarcoma (MS) and leukemia cutis (dermal infiltrates of blast cells) are 2 rare but well known manifestations of EMI. In MS, leukemic blasts infiltrate into various organ tissues (liver, spleen, gums, CNS), lymph node infiltration occurs in 12% cases of AML. Clinical features depend on the organs involved and the size of infiltration. Underlying molecular mechanisms and pathogenesis of EMI with spread of leukemic cells to certain specific tissues like the lymph nodes are not well understood. Diagnosis of EMI is made by immunohistochemistry of biopsy/cytology specimens demonstrating CD68-KP1 and MPO markers on malignant myeloid cells. Optimal therapy is unknown. For isolated MS, remission-induction chemotherapy same as AML is recommended. For MS concurrent with AML, induction chemotherapy +/- HCT are indicated. Targeted therapies do not have a clear role. CONCLUSIONS: EMI of lymph nodes is a rare cause of mediastinal lymphadenopathy in AML. Reference #1: Bakst RL, Tallman MS, Douer D, Yahalom J. How I treat extramedullary acute myeloid leukemia. Blood. 2011 Oct 6;118(14):3785-93. Reference #2: Yilmaz AF, Saydam G, Sahin F, Baran Y. Granulocytic sarcoma: a systematic review. Am J Blood Res. 2013 Dec 18;3(4):265-70. DISCLOSURE: The following authors have nothing to disclose: Anirudh Aron, Khawaja Muddassir No Product/Research Disclosure Information