en تخصصي Special گزارش مورد case report <div style="text-align: justify;"><span style="font-size:14px;"><span style="font-family:times new roman;"><span style="color:#008080;"><strong><em>Background:</em></strong> </span>Tumor lysis syndrome (TLS) which mostly occurs in lymphoproliferative malignancies after the start of chemotherapy is an oncologic emergency. Manifestations of metabolic imbalance including increasing hyperkalemia, hyperphosphatemia, hyperuricemia and hypocalcemia are common presentation of TLS.<br> <span style="color:#008080;"><strong><em>Case report:</em></strong></span> We present two cases of spontaneous TLS; a rare presentation of TLS before cytotoxic chemotherapy. These cases were admitted with presentation of TLS without any history of chemotherapy with mediastinal mass in chest X-ray (CXR) and subsequent diagnosis of lymphoblastic lymphoma and T-cell acute lymphocytic leukemia (ALL). After several hemodialysis sessions, their conditions were improved and they underwent chemotherapy.<br> <span style="color:#008080;"><strong><em>Conclusions:</em></strong> </span>It was found that the presentation of mediastinal mass in cases of lymphoma and acute leukemia might be associated with TLS before chemotherapy. In addition, it is important to pay attention to CXR, when we face to a patient with acute renal failure related to TLS.</span></span></div> Childhood Neoplasms, Leukemia, Lymphoma, Tumor Lysis Syndrome 313 316 http://caspianjp.ir/browse.php?a_code=A-10-78-3&slc_lang=en&sid=1 Ahmad Tamaddoni drtamaddoni@yahoo.com 10031947532846002688 10031947532846002688 No Assistant Professor in Pediatric Hematology, Non-Communicable Pediatric Diseases Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, IR Iran. Sahar Sadr Moharrerpour drsaharsadr@gmail.com 10031947532846002689 10031947532846002689 Yes Assistant Professor in Pediatric Nephrology, Non-Communicable Pediatric Diseases Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, IR Iran. Samane Asefi asefi_samane@yahoo.com 10031947532846002690 10031947532846002690 No Resident of Pediatric, Student Research Committee, Babol University of Medical Sciences, Babol, IR Iran. Babak Tamaddoni babitamaddoni@gmail.com 10031947532846002691 10031947532846002691 No Medical Student, Shahid Beheshti University of Medical Science