en Oncology Oncology case report case report <span style="font-size:14px;"><span style="font-family:Times New Roman;"><span style="color:#0000ff;"><strong><em>Background</em></strong><em>:</em></span> It is a rare cardiac malignant primary tumor that seems to derive from the same cellular line as myxomas, but the prognosis is very different. It is a rare cardiac malignant primary tumor that seems to derive from the same cellular line as myxomas, but the prognosis is very different. It is a rare cardiac malignant primary tumor that seems to derive from the same cellular line as myxomas, but the prognosis is very different. Cardiac myxosarcoma is a rare neoplasm that appears to rise from the same cellular source like myxoma. It is difficult to differentiate a myxoma tumor from a myxosarcoma tumor because of its appearance and pathology examination. Myxosercoma tumor requires surgery and chemoradiotherapy, but myxoma is treated only by surgery.<br> <span style="color:#0000ff;"><strong><em>Case Presentation</em></strong><em>:</em></span> We describe a case of a 58-year-old patient with a left atrium myxosarcoma, presenting with congestive heart failure. Transthoracic echocardiogram (TTE) showed a large polypoid and mobile mass in the left atrium, the patient underwent cardiac surgery and the tumor was successfully extracted, and histopathological result revealed typical features of myxoma. 15 days after surgery, he underwent explorative laparatomy because of progressive GI bleeding. Laparatomy revealed extensive metastatic masses in abdomen and the pathology diagnoses was myxosaroma. Unfortunately, in spite of supportive care, the patient expired on postoperative day one.<br> <span style="color:#0000ff;"><strong><em>Conclusion</em></strong><em>:</em></span> It is difficult to differentiate a myxoma tumor from a myxosarcoma tumor because of its appearance and pathology examination. Maybe magnetic resonance imaging can help us to achieve more data suggesting malignancy.</span></span> Pneumomediastinum, Pneumopericardium, Subcutaneous emphysema, acute lymphoblastic leukemia 379 382 http://caspjim.com/browse.php?a_code=A-10-1455-1&slc_lang=en&sid=1 Mohammad Kajiyazdi mkajiyazdi50@gmail.com 100319475328460031160 100319475328460031160 No Pediatric Hematology and Oncology Ward, Bahrami Children Hospital, Tehran University of Medical Sciences, Tehran, Iran Amir Hossein Norooznezhad norooznezhad@gmail.com 100319475328460031161 100319475328460031161 Yes Medical Biology Research Center, Health Technology Institute, Kermanshah University of Medical Sciences, Kermanshah, Iran