Tumor lysis syndrome
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In medicine (oncology and hematology), tumor lysis syndrome is a complication of chemotherapy to particularly large tumors (e.g. bulky lymphomas), although it occasionally occurs spontaneously. Breakdown products (lysis) of the cancer cells enter the bloodstream; many are biochemically active substances.
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Signs and symptoms
Vomiting, weakness/malaise, decreased urine production, convulsions. Symptoms progress, leading to coma and death if untreated.
In patients who are being treated for massive lesions, prophylaxis with allopurinol may already have been given (see below).
Diagnosis
Blood tests done when tumor lysis syndrome is suspected generally include full blood count, renal function (creatinine), electrolytes, blood urea nitrogen, uric acid, calcium, phosphate, and albumin (to correct calcium levels).
Tumor lysis syndrome features elevated uric acid (hence gout), potassium and phosphate and low calcium due to precipitation with the phosphate.
Pathogenesis
When compared to blood and extracellular fluid, cells are relatively high in potassium and phosphates, as both are required for cellular function. High turnover of cells leads to an increase in these in the blood.
Uric acid is a breakdown product of DNA, converted by xanthine oxidase from xanthine and hypoxanthine, which are in turn purine breakdown producs. Uric acid is more toxic to tissues than (hypo)xanthine. Oddly, gout is not a feature of tumor lysis; the high uric acid levels that cause gout probably need to be present for an extended period of time before the putative crystals can develop.
Prophylaxis and treatment
Follow-up of patients at risk consists of regular checking of urine production and blood pressure.
Patients with bulky lesions may require intravenous fluids (3 liters a day) and possibly allopurinol, an inhibitor of xanthine oxidase, which limits formation of uric acid. Elimination of waste products may possibly be accelerated by forced alkaline diuresis, e.g. administering bicarbonate to speed up urine production, and diuretics (but thiazides interfere with uric acid elimination and must be avoided).
In severe tumor lysis syndrome, individual abnormalities may need immediate treatment.
- Hyperkalemia and high phosphate levels may eventually require dialysis
- Hypocalcemia may require intravenous calcium gluconate and vitamin D3
- High uric acid may respond to rasburicase, a synthetic urate oxidase enzyme. Its role in prophylaxis is undetermined.