tumor lysis syndrome ( tls ) is an oncologic emergency that frequently occurs in patients with a rapidly proliferating malignancy , commonly hematologic , after the initiation of cytotoxic therapy . tls is characterized by a massive release of intracellular potassium , phosphate , and nucleic acid metabolites into the systemic circulation , which can result in cardiac arrhythmia , seizure , or acute renal failure , all of which could be life - threatening . . however , spontaneous lysis of solid tumors is considered rare . herein , we present a case of spontaneous tls in a 55-year - old woman that occurred shortly after she was diagnosed with metastatic small cell lung cancer . a 55-year - old female smoker with a history of chronic obstructive pulmonary disease and diabetes presented to the emergency department with worsening dyspnea and respiratory distress . a physical examination revealed wheezing and decreased breath sounds in the left upper lung field . she was admitted to the intensive care unit and started receiving intravenous antibiotics , fluid resuscitation , and noninvasive ventilatory support . owing to right upper quadrant pain and a high alkaline phosphate level , once the patient 's condition stabilized , chest and abdomen computed tomography examinations were performed , which showed a 7-cm mass in the left upper lung lobe associated with obstructive pneumonitis involving much of the left upper lobe ( fig . 1 ) as well as extensive bilateral mediastinal and left hilar , axillary , and supraclavicular lymphadenopathy and multiple liver metastases . histopathologic examination of a liver biopsy specimen indicated high - grade small cell neuroendocrine cancer . magnetic resonance imaging of the brain yielded normal findings . finally , the diagnosis was established as extensive stage small cell lung cancer . on hospital day 4 , however , oliguria was detected . serum biochemistry tests showed elevated creatinine and potassium levels , and therefore , sepsis - associated acute kidney injury was initially considered . subsequent laboratory examinations revealed increasing levels of potassium ( maximum 5.6 meq / l ) , phosphorus ( maximum 8.4 mg / dl ) , and uric acid ( maximum 11.3 mg / dl ) . accordingly , spontaneous tls was diagnosed on the basis of the characteristic symptom of multiple electrolyte - related abnormalities . aggressive treatment in the form of fluid resuscitation , phosphate binders , allopurinol , and rasburicase was initiated . nonetheless , her renal function continued to deteriorate , with the creatinine level increasing from 0.5 mg / dl upon admission to 7.9 mg / dl over 6 days . the departments of oncology and nephrology were consulted , and the consensus was to conduct daily hemolysis after the first cycle of palliative chemotherapy comprising cisplatin and etoposide . the patient in this case demonstrated spontaneous tls caused by small cell lung cancer , which is a highly proliferative solid tumor . the patient had oliguric renal failure and characteristic laboratory abnormalities including hyperkalemia , hyperuricemia , and hyperphosphatemia in the setting of widespread metastatic disease . to the best of our knowledge , only 4 case reports of spontaneous tls associated with small cell lung cancer have been reported in the literature [ 3 , 4 , 5 , 6 ] . typically , tls results from the massive release of intracellular electrolytes and metabolites when large numbers of tumor cells are lysed by cytotoxic chemotherapy or , rarely , spontaneously . most commonly , tls occurs in cases of rapidly growing malignancies with a high tumor burden , especially hematologic malignancies such as burkitt lymphoma or acute lymphoblastic leukemia . however , cases of tls involving solid tumors have been reported in the literature [ 7 , 8 ] . the classic findings of tls are hyperkalemia , hyperphosphatemia with secondary hypocalcemia , and hyperuricemia . these electrolyte abnormalities can lead to cardiac arrhythmia , seizure , or acute renal failure , all of which could be life - threatening without prompt recognition and treatment . the risk factors for tls include bulky tumors , extensive metastatic diseases including visceral or bone marrow involvement , elevated serum uric acid or lactate dehydrogenase levels , high white blood cell count ( > 50,000 cells/l ) , tumors with a high sensitivity to antineoplastic treatment , and underlying renal dysfunction . tls involving solid tumors is assumed to share similar risk factors [ 8 , 9 ] , although its spontaneous occurrence in tumor types with relatively low response rates to cytotoxic therapy or without the classic rapid growth kinetics , such as that observed in hepatocellular , pancreatic , ovarian cancer , and malignant melanoma , has been reported . in our patient , the risk factors included extensive metastatic disease and small cell lung cancer , a rapidly proliferative tumor cell type . although rare , tls involving solid tumors is associated with a higher mortality rate than that reported for hematologic malignancies . current guidelines emphasize both preventive measures and monitoring for high - risk patients undergoing chemotherapy [ 1 , 2 ] . allopurinol , a xanthine oxidase inhibitor , or rasburicase can be used to lower the serum uric acid level . hemodialysis is an option for patients who develop severe renal failure or refractory electrolyte abnormalities , as in our patient . in conclusion , spontaneous tls should be considered in the differential diagnosis for patients who demonstrate the classic electrolyte abnormalities or renal failure in the setting of malignancy even without cytotoxic treatment , as observed in our case . prophylactic treatment could be a suitable option for patients with multiple risk factors for spontaneous tls . the authors declare that there is no conflict of interest regarding the publication of this article .