Clinical emergencies in children with cancer

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What is tumor lysis syndrome?

Tumor lysis syndrome (TLS) is defined by the metabolic derangements that result from massive release of intracellular contents into the systemic circulation secondary to the initiation of cytotoxic therapy. The laboratory findings of TLS include hyperuricemia, hyperkalemia, hyperphosphatemia, hypocalcemia, and an increasing serum creatinine; clinically, TLS may cause renal failure, cardiac arrhythmias, seizures, or sudden death. Serum lactate dehydrogenase (LDH) is not a component of the syndrome; however, it can be used as a risk assessment surrogate for rapid cell turnover. Occasionally, in situations where the initial tumor burden is extremely high, such as in Burkitt lymphoma, acute lymphoblastic leukemia (ALL) with white blood cell (WBC) count greater than 100,000/mm ³ , and acute myelogenous leukemia (AML) with WBC greater than 50,000/mm ³ , a phenomenon referred to as hyperleukocytosis, TLS may occur spontaneously.

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Describe the management of TLS.

It is imperative to perform a tumor lysis risk assessment at the time of initial presentation and disease diagnosis. Risk should be assessed based on patient comorbidities, laboratory criteria, tumor type, cell burden, cell lysis potential, rate of proliferation, and degree of renal impairment. Continuous monitoring, a high index of suspicion, and preparation for early intervention are mandatory. The most important measures are ensuring adequate urine output and the use of hypouricemic agents. Allopurinol, a xanthine analog, works as a competitive xanthine oxidase inhibitor, slowing the production of uric acid and decreasing the risk of acid crystallization in kidney tubules. Rasburicase is the preferred prophylactic agent in cases of high-risk TLS and as treatment in patients with hyperuricemia. Rasburicase is a recombinant urate oxidase that catalyzes the oxidation of uric acid to allantoin, which is 5 to 10 times more urine soluble than uric acid. G6PD screening should always be performed to prevent methemoglobinemia or severe hemolytic anemia. Allopurinol should be stopped if rasburicase is started.

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