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The tumor lysis syndrome is the most common disease-related emergency encountered by physicians caring for children or adults with hematologic cancers.1-4 Although it develops most often in patients with non-Hodgkin’s lymphoma or acute leukemia, its frequency is increasing among patients who have tumors that used to be only rarely associated with this complication.5-8 The tumor lysis syndrome occurs when tumor cells release their contents into the bloodstream, either spontaneously or in response to therapy, leading to the characteristic findings of hyperuricemia, hyperkalemia, hyperphosphatemia, and hypocalcemia.1-3 These electrolyte and metabolic disturbances can progress to clinical toxic effects, including renal insufficiency, cardiac arrhythmias, seizures, and death due to multiorgan failure.
Although optimal methods of risk classification and treatment have been difficult to define, uniform standards for management of the tumor lysis syndrome are beginning to evolve. Indeed, several groups have advocated guidelines for risk stratification and made recommendations for evaluating risk and for prophylactic therapy for the tumor lysis syndrome.2,9 This review of the tumor lysis syndrome summarizes current strategies for risk assessment, prophylaxis, and therapy. The following case illustrates the clinical challenges.
An 8-year-old boy was referred to an otolaryngologist for tonsillectomy after several months of increased snoring, fatigue, sore throat, enlarged tonsils, and gradually increasing painless and nontender cervical lymphadenopathy. Two days before the scheduled procedure, his parents took him to the local emergency department after he had been unable to sleep because of congestion, sore throat, and difficulty breathing. The physician in the emergency department documented nasal congestion, enlarged tonsils that touched in the midline, and significant anterior and posterior cervical adenopathy. Dexamethasone (4 mg) was administered intramuscularly, and loratadine was prescribed. During the next 36 hours, the patient’s congestion and breathing improved somewhat, but malaise developed and he vomited repeatedly. He returned to the emergency department, where he appeared ill and was found to be moderately dehydrated. Evaluation showed a white-cell count of 84,600 per cubic millimeter, with circulating lymphoblasts; a sodium level of 133 mmol per liter; potassium, 5.9 mmol per liter; bicarbonate, 16 mmol per liter; creatinine, 1.0 mg per deciliter (88.4 μmol per liter); phosphorus, 8.5 mg per deciliter (2.7 mmol per liter); calcium, 6.7 mg per deciliter (1.7 mmol per liter); uric acid, 12.3 mg per deciliter (732 μmol per liter); and lactate dehydrogenase, 4233 IU per liter. Chest radiography revealed a small mediastinal mass, and an electrocardiogram was normal. The patient was given two boluses of normal saline (20 ml per kilogram of body weight), rasburicase (0.15 mg per kilogram), and 800 mg of aluminum hydroxide; intravenous fluids (2500 ml per square meter of body-surface area per day) were administered, and he was transferred by ambulance to a tertiary care center, where he was admitted to the intensive care unit and T-cell acute lymphoblastic leukemia was diagnosed. His course was complicated by oliguria, hyperphosphatemia (a peak of 11.2 mg per deciliter [3.6 mmol per liter] of phosphorus, on day 3), an increased creatinine level (a peak of 3.8 mg per deciliter [318.2 μmol per liter], on day 5), and hypertension that resolved after 2 months. He did not require dialysis, and more than 5 years after diagnosis, he remains in remission.
In the current classification system of Cairo and Bishop,10 the tumor lysis syndrome can be classified as laboratory or clinical (Table 1). Laboratory tumor lysis syndrome requires that two or more of the following metabolic abnormalities occur within 3 days before or up to 7 days after the initiation of therapy: hyperuricemia, hyperkalemia, hyperphosphatemia, and hypocalcemia. Clinical tumor lysis syndrome is present when laboratory tumor lysis syndrome is accompanied by an increased creatinine level, seizures, cardiac dysrhythmia, or death. A few refinements could improve this classification. First, it should be stipulated that two or more metabolic abnormalities be present simultaneously, because some patients may present with one abnormality, but later another one may develop that is unrelated to the tumor lysis syndrome (e.g., hypocalcemia associated with sepsis). Second, in contrast to Cairo and Bishop’s definition, a 25% change from baseline should not be considered a criterion, since such increases are rarely clinically important unless the value is already outside the normal range. Third, any symptomatic hypocalcemia should constitute clinical tumor lysis syndrome. Our patient met the criteria for laboratory tumor lysis syndrome when he returned to the emergency department, and he met the criteria for clinical tumor lysis syndrome the next day, when his creatinine level increased from 1.0 mg per deciliter to 2.1 mg per deciliter (185.6 μmol per liter).
When cancer cells lyse, they release potassium, phosphorus, and nucleic acids, which are metabolized into hypoxanthine, then xanthine, and finally uric acid, an end product in humans (Fig. 1).12 Hyperkalemia can cause serious — and occasionally fatal — dysrhythmias. Hyperphosphatemia can cause secondary hypocalcemia, leading to neuromuscular irritability (tetany), dysrhythmia, and seizure, and can also precipitate as calcium phosphate crystals in various organs (e.g., the kidneys, where these crystals can cause acute kidney injury).13 Uric acid can induce acute kidney injury not only by intrarenal crystallization but also by crystal-independent mechanisms, such as renal vaso-constriction, impaired autoregulation, decreased renal blood flow, oxidation, and inflammation.14-16 Tumor lysis also releases cytokines that cause a systemic inflammatory response syndrome and often multiorgan failure.17-19
The tumor lysis syndrome occurs when more potassium, phosphorus, nucleic acids, and cytokines are released during cell lysis than the body’s homeostatic mechanisms can deal with. Renal excretion is the primary means of clearing urate, xanthine, and phosphate, which can precipitate in any part of the renal collecting system. The ability of kidneys to excrete these solutes makes clinical tumor lysis syndrome unlikely without the previous development of nephropathy and a consequent inability to excrete solutes quickly enough to cope with the metabolic load.
Crystal-induced tissue injury occurs in the tumor lysis syndrome when calcium phosphate, uric acid, and xanthine precipitate in renal tubules and cause inflammation and obstruction (Fig. 2).20,23 A high level of solutes, low solubility, slow urine flow, and high levels of cocrystallizing substances favor crystal formation and increase the severity of the tumor lysis syndrome.24-26 High levels of both uric acid and phosphate render patients with the tumor lysis syndrome at particularly high risk for crystal-associated acute kidney injury, because uric acid precipitates readily in the presence of calcium phosphate, and calcium phosphate precipitates readily in the presence of uric acid. Also, higher urine pH increases the solubility of uric acid but decreases that of calcium phosphate. In patients treated with allopurinol, the accumulation of xanthine, which is a precursor of uric acid and has low solubility regardless of urine pH, can lead to xanthine nephropathy or urolithiasis (Fig. 1).20,27
Calcium phosphate can precipitate throughout the body (Fig. 2). The risk of ectopic calcification is particularly high among patients who receive intravenous calcium.13 When calcium phosphate precipitates in the cardiac conducting system, serious, possibly fatal, dysrhythmias can occur. Acute kidney injury developed in our patient as a result of the precipitation of uric acid crystals and calcium phosphate crystals and was exacerbated by dehydration and acidosis that developed because the tumor lysis syndrome had not been suspected and no supportive care was provided.
The incidence and severity of the tumor lysis syndrome depend on the cancer mass, the potential for lysis of tumor cells, the characteristics of the patient, and supportive care (Table 2). The variability of patient cohorts and lack of standard criteria have contributed to a wide range of reported incidences (see Table 1 in the Supplementary Appendix, available with the full text of this article at NEJM.org).28 The greater the cancer mass, the greater the quantity of cellular contents released after the administration of effective anticancer therapy. Cancers with a high potential for cell lysis include high-grade lymphomas, acute leukemias, and other rapidly proliferating tumors. However, the potential for cell lysis must be considered along with the effectiveness of therapy, as highlighted by a case of tumor lysis syndrome in an adult who died after treatment with cetuximab for metastatic colon carcinoma, a cancer in which the tumor lysis syndrome had not been previously reported.5 Indeed, the tumor lysis syndrome increasingly has been reported in patients with cancers that previously had been rarely associated with this complication, such as endometrial cancer, hepatocellular carcinoma, chronic lymphocytic leukemia, and chronic myelogenous leukemia.5-8,29-32 Characteristics of patients that confer high risk include preexisting chronic renal insufficiency, oliguria, dehydration, hypotension, and acidic urine.
The adequacy of fluid management affects both the development and the severity of the tumor lysis syndrome. Thus, disastrous cases of the tumor lysis syndrome occurred in patients with nonhematologic cancer who received effective anticancer treatment but no intravenous fluids or monitoring because the tumor lysis syndrome was not anticipated.5,32 In contrast, in many countries, patients with a bulky Burkitt’s lymphoma who have a high potential for lysis have a low risk of clinical tumor lysis syndrome because they routinely receive aggressive treatment with hydration and rasburicase, a recombinant urate oxidase enzyme that is a highly effective uricolytic agent (Table 1 in the Supplementary Appendix). Children with Burkitt’s lymphoma who received rasburicase were a fifth as likely to undergo dialysis as those who received allopurinol, illustrating the dramatic difference that supportive care can make, even when other risk factors for the tumor lysis syndrome are the same.33 This was seen in the 8-year-old boy in the vignette.
Acute kidney injury is associated with high morbidity and mortality,34 and its prevention requires an awareness of the patient’s a priori risk of the tumor lysis syndrome and careful monitoring for early signs of it. Models that predict the risk of the tumor lysis syndrome have been developed for adults with acute myeloid leukemia35,36 and children with acute lymphoblastic leukemia37 treated with hydration and allopurinol (but not rasburicase). These models lack a standard definition of the tumor lysis syndrome, use different primary end points (i.e., either clinical tumor lysis syndrome or any type of the tumor lysis syndrome), lack standardized supportive care guidelines, and have complex scoring systems. Experts have issued management guidelines for the tumor lysis syndrome,2,9,38 but further guidance awaits simple risk-prediction models that have a standardized definition of the tumor lysis syndrome and uniform supportive care guidelines for each cancer type.28 We present a practical approach for clinicians (Fig. 3, and Table 2 in the Supplementary Appendix).
Optimal management of the tumor lysis syndrome should involve preservation of renal function. Management should also include prevention of dysrhythmias and neuromuscular irritability (Fig. 3).
All patients who are at risk for the tumor lysis syndrome should receive intravenous hydration to rapidly improve renal perfusion and glomerular filtration and to minimize acidosis (which lowers urine pH and promotes the precipitation of uric acid crystals) and oliguria (an ominous sign). This is usually accomplished with hyperhydration by means of intravenous fluids (2500 to 3000 ml per square meter per day in the patients at highest risk). Hydration is the preferred method of increasing urine output, but diuretics may also be necessary. In a study involving a rat model of urate nephropathy with elevated serum uric acid levels induced by continuous intravenous infusion of high doses of uric acid, high urine output due to treatment with high-dose furosemide or congenital diabetes insipidus (in the group of mice with this genetic modification) protected the kidneys equally well, whereas acet-azolamide (mild diuresis) and bicarbonate provided only moderate renal protection (no more than a low dose of furosemide without bicarbonate).39 Hence, in patients whose urine output remains low after achieving an optimal state of hydration, we recommend the use of a loop diuretic agent (e.g., furosemide) to promote diuresis, with a target urine output of at least 2 ml per kilogram per hour.
Reducing the level of uric acid, with the use of allopurinol and particularly with the use of rasburicase, can preserve or improve renal function and reduce serum phosphorus levels as a secondary beneficial effect.40 Although allopurinol prevents the formation of uric acid, existing uric acid must still be excreted. The level of uric acid may take 2 days or more to decrease, a delay that allows urate nephropathy to develop (Fig. 1b in the Supplementary Appendix). Moreover, despite treatment with allopurinol, xanthine may accumulate, resulting in xanthine nephropathy.13,20,27 Since the serum xanthine level is not routinely measured, its effect on the development of acute kidney injury is uncertain. By preventing xanthine accumulation and by directly breaking down uric acid, rasburicase is more effective than allopurinol for the prevention and treatment of the tumor lysis syndrome. In a randomized study of the use of allopurinol versus rasburicase for patients at risk for the tumor lysis syndrome, the mean serum phosphorus level peaked at 7.1 mg per deciliter (2.3 mmol per liter) in the rasburicase group (and mean uric acid levels decreased by 86%, to 1 mg per deciliter [59.5 μmol per liter] at 4 hours) as compared with 10.3 mg per deciliter (3.3 mmol per liter) in the allopurinol group (and mean uric acid levels decreased by 12%, to 5.7 mg per deciliter [339.0 μmol per liter] at 48 hours).41,42 The serum creatinine level improved (decreased) by 31% in the rasburicase group but worsened (increased) by 12% in the allopurinol group. Pui and colleagues40 documented no increases in phosphorus levels and decreases in creatinine levels among 131 patients who were at high risk for the tumor lysis syndrome and were treated with rasburicase. Finally, in a multicenter study involving pediatric patients with advanced-stage Burkitt’s lymphoma, in which all patients received identical treatment with chemotherapy and aggressive hydration, the tumor lysis syndrome occurred in 9% of 98 patients in France (who received rasburicase) as compared with 26% of 101 patients in the United States (who received allopurinol) (P=0.002).33 Dialysis was required in only 3% of the French patients but 15% of the patients in the United States (P=0.004). At the time of the study, rasburicase was not available in the United States.
Urinary alkalinization increases uric acid solubility but decreases calcium phosphate solubility (Fig. 1a in the Supplementary Appendix). Because it is more difficult to correct hyperphosphatemia than hyperuricemia, urinary alkalinization should be avoided in patients with the tumor lysis syndrome, especially when rasburicase is available.13 Whether urine alkalinization prevents or reduces the risk of acute kidney injury in patients without access to rasburicase is unknown, but the animal model of urate nephropathy suggested no benefit.39 If alkalinization is used, it should be discontinued when hyperphosphatemia develops. In patients treated with rasburicase, blood samples for the measurement of the uric acid level must be placed on ice to prevent ex vivo breakdown of uric acid by rasburicase and thus a spuriously low level. Patients with glucose-6-phosphate dehydrogenase deficiency should avoid rasburicase because hydrogen peroxide, a breakdown product of uric acid, can cause methemoglobinemia and, in severe cases, hemolytic anemia.43,44 Rasburicase is recommended as first-line treatment for patients who are at high risk for clinical tumor lysis syndrome.9 Because of cost considerations and pending pharmacoeconomic studies, no consensus has been reached on rasburicase use in patients who are at intermediate risk for the tumor lysis syndrome; some have advocated use of a small dose of rasburicase in such patients.45,46 Patients who are at low risk can usually be treated with intravenous fluids with or without allopurinol, but they should be monitored daily for signs of the tumor lysis syndrome.
Hyperkalemia remains the most dangerous component of the tumor lysis syndrome because it can cause sudden death due to cardiac dysrhythmia. Patients should limit potassium and phosphorus intake during the risk period for the tumor lysis syndrome.47 Frequent measurement of potassium levels (every 4 to 6 hours), continuous cardiac monitoring, and the administration of oral sodium polystyrene sulfonate are recommended in patients with the tumor lysis syndrome and acute kidney injury. Hemodialysis and hemofiltration effectively remove potassium. Glucose plus insulin or beta-agonists can be used as temporizing measures, and calcium gluconate may be used to reduce the risk of dysrhythmia while awaiting hemodialysis.
Hypocalcemia can also lead to life-threatening dysrhythmias and neuromuscular irritability; controlling the serum phosphorus level may prevent hypocalcemia. Symptomatic hypocalcemia should be treated with calcium at the lowest dose required to relieve symptoms, since the administration of excessive calcium increases the calcium–phosphate product and the rate of calcium phosphate crystallization, particularly if the product is greater than 60 mg2 per square deciliter (Fig. 2D and 2E). Hypocalcemia not accompanied by signs or symptoms does not require treatment. Despite the lack of studies that show the efficacy of phosphate binders in patients with the tumor lysis syndrome, this treatment is typically given. The role of renal phosphate leak in renal lithiasis and the use of phosphate binders have recently been reviewed in the Journal.48,49
Despite optimal care, severe acute kidney injury develops in some patients and requires renal replacement therapy (Table 3 in the Supplementary Appendix). Although the indications for renal-replacement therapy in patients with the tumor lysis syndrome are similar to those in patients with other causes of acute kidney injury, somewhat lower thresholds are used for patients with the tumor lysis syndrome because of potentially rapid potassium release and accumulation, particularly in patients with oliguria. In patients with the tumor lysis syndrome, hyperphosphatemia-induced symptomatic hypocalcemia may also warrant dialysis. Phosphate removal increases as treatment time increases, which has led some to advocate the use of continuous renal-replacement therapies in patients with the tumor lysis syndrome, including continuous venovenous hemofiltration, continuous venovenous hemodialysis, or continuous venovenous hemodiafiltration.50 These methods of dialysis use filters with a larger pore size, which allows more rapid clearance of molecules that are not efficiently removed by conventional hemodialysis (Table 3 in the Supplementary Appendix). One study that compared phosphate levels among adults who had acute kidney injury that was treated with either conventional hemodialysis or continuous venovenous hemodiafiltration showed that continuous venovenous hemodiafiltration more effectively reduced phosphate.51 Much less is known about the dialytic clearance of uric acid, but in countries where rasburicase is available, hyperuricemia is seldom an indication for dialysis.40,44,52 In our patient, once the tumor lysis syndrome was identified, treatment with intravenous fluids, phosphate binders, and rasburicase prevented the need for dialysis. Despite a potassium level of 5.9 mmol per liter, he had no dysrhythmia or changes on electrocardiography, but had he presented 1 day later, the tumor lysis syndrome may have proved fatal.
Urine output is the key factor to monitor in patients who are at risk for the tumor lysis syndrome and in those in whom the syndrome has developed. In patients whose risk of clinical tumor lysis syndrome is non-negligible, urine output and fluid balance should be recorded and assessed frequently. Patients at high risk should also receive intensive nursing care with continuous cardiac monitoring and the measurement of electrolytes, creatinine, and uric acid every 4 to 6 hours after the start of therapy. Those at intermediate risk should undergo laboratory monitoring every 8 to 12 hours, and those at low risk should undergo such monitoring daily. Monitoring should continue over the entire period during which the patient is at risk for the tumor lysis syndrome, which depends on the therapeutic regimen. In a protocol for acute lymphoblastic leukemia, which featured up-front, single-agent methotrexate treatment,53 new-onset tumor lysis syndrome developed in some patients at day 6 or day 7 of remission-induction therapy (after the initiation of combination chemotherapy with prednisone, vincristine, and daunorubicin on day 5 and asparaginase on day 6).
Patients at high risk for the tumor lysis syndrome may also receive low-intensity initial therapy. Slower lysis of the cancer cells allows renal homeostatic mechanisms to clear metabolites before they accumulate and cause organ damage. This strategy, in cases of advanced B-cell non-Hodgkin’s lymphoma or Burkitt’s leukemia, has involved treatment with low-dose cyclophosphamide, vincristine, and prednisone for a week before the start of intensive chemotherapy. Similarly, many groups subscribe to a week of prednisone monotherapy for childhood acute lymphoblastic leukemia.
Supported in part by grants (CA21765 and U01 GM92666) from the National Institutes of Health and by the American Lebanese Syrian Associated Charities.
Dr. Howard reports receiving consulting fees from EnzymeRx and Sanofi-Aventis.
Disclosure forms provided by the authors are available with the full text of this article at NEJM.org.