B48-21 Spontaneous Tumor Lysis Syndrome in a Patient With Metastatic Well-differentiated Grade 2 Neuroendocrine Tumor

Abstract Introduction Tumor lysis syndrome (TLS) is a life-threatening oncologic emergency caused by massive tumor cell breakdown, leading to hyperuricemia, hyperphosphatemia, hyperkalemia, and secondary hypocalcemia that can trigger acute renal failure, arrhythmias, or seizures. It typically follows cytotoxic therapy in rapidly proliferating hematologic malignancies. In contrast, spontaneous TLS (sTLS) occurs without recent treatment and is extremely rare in solid tumors. Its development in well- differentiated neuroendocrine tumors (NETs) is exceptionally uncommon, underscoring the importance of early recognition even in slow-growing metastatic malignancies with high tumor burden. Case Report A 57-year-old man with hypertension, obstructive sleep apnea, and recentlydiagnosed metastatic grade 2 NET (liver, lung, bone), confirmed on liver biopsy, presented with one day of progressive weakness, confusion, and diffuse pain. Eleven days earlier he had received a single octreotide injection, without any chemotherapy or radiotherapy. Examination revealed jaundice and lethargy. Laboratory testing showed BUN 118 mg/dL, creatinine 7.3 mg/dL, uric acid 17.5 mg/dL, phosphorus 12.5 mg/dL, calcium 6.3 mg/dL, AST/ALT 723/448 U/L, total bilirubin 9.5 mg/dL, LDH 3984 U/L, and INR 1.9, fulfilling Cairo-Bishop criteria for TLS. Despite aggressive IV fluids and high-dose furosemide, urine output was 100 mL/day. He received Rasburicase 6 mg IV and continuous renal replacement therapy (CRRT), resulting in improved mentation and metabolic parameters. Cultures andimaging showed no infection or new lesions. Discussion and Importance This case highlights an exceptionally rare presentation of spontaneous tumor lysis syndrome (sTLS) in a low-grade solid malignancy, challenging the expected indolent behavior of well-differentiated neuroendocrine tumors. The patient’s abrupt metabolic decompensation, despite the absence of recent cytotoxic therapy, demonstrates thatextensive tumor burden and intrinsic necrosis can independently precipitate severe electrolyte and renal disturbances. This underscores the importance of maintaining a high index of suspicion for sTLS in metastatic solid tumors. Prompt clinical recognition, early initiation of Rasburicase, and timely renal replacement therapy are vital to prevent irreversible renal injury and improve outcomes in this rare but potentially fatal presentation. This abstract is funded by: None