Urine Xanthine Crystals in Hematologic Malignancies with Tumor Lysis Syndrome

Tumor lysis syndrome (TLS) is a metabolic disorder caused by massive tumor lysis. Hypouricemic agents are administered to prevent TLS-related hyperuricemia and renal failure. We experienced three cases of urine xanthine crystals during TLS in patients with hematologic malignancies who received prophylactic fe-buxostat. Yellowish and pinkish deposits were observed in urinary tract catheters and urinary bags. Urine mi-croscopy revealed that the deposits were xanthine crystals. In rapid tumor lysis, inhibition of xanthine oxi-dase can cause xanthine accumulation and urine xanthine crystallization. During TLS, urine xanthine crystals may be overlooked, so careful observation and management are required to avoid xanthine nephropathy.