Abstract Body (Do not enter title and authors here): A 65-year-old male with history of coronary artery disease with percutaneous coronary intervention six months earlier presented with one month of fevers, night sweats, chest pain, muscle aches, fatigue, dyspnea on exertion and palpitations. CT chest revealed a 9x5cm mass in the right atrium and right ventricle, which was confirmed on TTE. He had a TTE two weeks earlier without evidence of a mass. Cardiac MRI further revealed a large pericardial effusion and the cardiac mass encasing the right coronary artery and superior vena cava causing near occlusion of the distal SVC. A biopsy and pericardiocentesis revealed acute leukemia of ambiguous lineage, but bone marrow biopsy and serial lumbar punctures were negative for disease. The patient underwent treatment with intravenous and intrathecal chemotherapy. His course was complicated by atrial fibrillation with rapid ventricular response requiring a rate control strategy as his chemotherapy-induced thrombocytopenia prevented anticoagulation. Initial restaging scans one to three months after chemotherapy showed resolution of uptake and reduction in mass size. However, subsequent scans one month after prior scans showed the mass to have increased uptake and size, so partial resection was performed with repeat pathology confirming acute leukemia of ambiguous lineage. Initial plans for bone marrow transplant were placed on hold given local recurrence. Currently, he is receiving palliative radiation as a bridge with hope for more targeted therapy.

Acute undifferentiated leukemia is exceedingly rare and is defined as an absence of definitive myeloid or lymphoid lineage markers. There has never been a reported case of acute undifferentiated leukemia presenting as an isolated cardiac mass as seen in this case. Cardiac involvement in leukemia is rare, and it is usually associated with a distinct myeloid or lymphoid lineage if discovered. Patients with cardiac involvement are frequently asymptomatic and cardiac involvement may only be noted during autopsy. Overall, outcomes for cardiac hematologic malignancies are poor but are slightly more favorable in leukemias.

Cardiac hematologic malignancies are exceedingly rare and can progress quickly. It is important to recognize them quickly and initiate definitive treatment plans as soon as possible to prevent local and metastatic recurrence. More research is needed to understand the progression of acute undifferentiated leukemia presenting as a cardiac mass.