Spontaneous Tumor Lysis Syndrome in a Critically Ill Patient With Cytology Favoring Small Cell Carcinoma: A Case Report

Tumor lysis syndrome (TLS) is a life-threatening metabolic emergency most commonly associated with hematologic malignancies and is rarely reported in solid tumors.We describe spontaneous TLS in a woman in her late 70s with chronic kidney disease, diabetes mellitus, and atrial fibrillation who presented with vasopressor-dependent shock and was found to have a large necrotic mediastinal mass with mediastinal lymphadenopathy and bilateral pulmonary nodules.Endobronchial ultrasound-guided transbronchial needle aspiration of mediastinal lymph nodes demonstrated malignancy favoring small cell carcinoma.She had received no anticancer therapy.Available pre-bronchoscopy laboratory measurements included potassium 4.5 mEq/L, phosphorus 3.0 mg/dL, uric acid 4.0 mg/dL, and calcium 8.8 mg/dL, without the characteristic biochemical pattern of TLS.Subsequently, she developed progressive hyperkalemia, hyperphosphatemia, modest hypocalcemia, severe metabolic acidosis, oliguria progressing to anuria, and worsening renal failure.Uric acid increased to a documented peak of 12 mg/dL, and lactate dehydrogenase reached 3,608 U/L.Rasburicase was administered, and continuous renal replacement therapy was initiated; however, the patient developed refractory shock and progressive multiorgan failure and died.This case highlights spontaneous tumor lysis syndrome (STLS) as a rare but potentially fatal complication of a bulky thoracic malignancy with cytology favoring small cell carcinoma, particularly in the setting of markedly impaired renal reserve.Bronchoscopy serves as a temporal landmark in the biochemical evolution of TLS, but a causal relationship cannot be established, and pre-existing shock, acute kidney injury, and possible sepsis were important concurrent contributors.