|
Advertisement |
|
|
||
 |
|
|||||
|
|||||
|
 |
||||||
|
||||||
|
||||||
|
© 2000 American Society for Clinical Oncology Hypersensitivity or Development of Antibodies to Asparaginase Does Not Impact Treatment Outcome of Childhood Acute Lymphoblastic LeukemiaFrom the Departments of Pharmaceutical Sciences, Hematology-Oncology, and Biostatistics and Epidemiology, St. Jude Children’s Research Hospital, and Colleges of Pharmacy and Medicine, University of Tennessee, Memphis, TN. Address reprint requests to Mary V. Relling, PharmD, Pharmaceutical Department, St. Jude Children’s Research Hospital, 332 N Lauderdale, Memphis, TN 38105; email mary.relling{at}stjude.org
PURPOSE: Development of antibodies and hypersensitivity to asparaginase are common and may attenuate asparaginase effect. Our aim was to determine the relationship between antiasparaginase antibodies or hypersensitivity reactions and event-free survival (EFS). PATIENTS AND METHODS: One hundred fifty-four children with acute lymphoblastic leukemia received Escherichia coli asparaginase 10,000 IU/m2 intramuscularly three times weekly for nine doses during multiagent induction and reinduction phases and for seven monthly doses during continuation treatment. Erwinia asparaginase was used in case of clinical hypersensitivity to E coli but not for subclinical development of antibodies. Plasma antiasparaginase antibody concentrations were measured on day 29 of induction in 152 patients. RESULTS: Antibodies were detectable in 54 patients (35.5%), of whom 30 (55.6%) exhibited hypersensitivity to asparaginase. Of the 98 patients who had no detectable antibodies, 18 (18.4%) had allergic reactions. Patients with antibodies were more likely to have a reaction than those without antibodies (P < .001). Among the 50 patients who experienced allergic reactions (including two for whom antibodies were not measured), 36 (72.0%) were subsequently given Erwinia asparaginase; seven (19.4%) reacted to this preparation. EFS did not differ among patients who did and did not have antibodies (P = .54), with 4-year EFS (± 1 SE) of 83% ± 6% and 76% ± 5%, respectively. Similarly, EFS did not differ among patients who did and did not develop allergic reactions (P = .68), with 4-year estimates of 82% ± 6% and 78% ± 5%, respectively. CONCLUSION: In this setting, in which most patients with allergy were switched to another preparation, there was no adverse prognostic impact of clinical or subclinical allergy to asparaginase.
ASPARAGINASE IS an effective antileukemic agent that exploits a metabolic difference between normal cells and malignant cells. Asparaginase catalyzes the hydrolysis of asparagine to aspartic acid and ammonia in the extracellular space. Although most normal cells can synthesize asparagine, asparagine synthetase activity or inducibility is diminished in some malignant lymphoblasts such that this amino acid is not produced in sufficient quantities in leukemic cells.1,2 As a result of asparagine depletion, synthesis of protein and nucleic acids is diminished, which decreases leukemic cell proliferation. Because asparaginase is isolated from bacterial sources (Escherichia coli or Erwinia chrysanthemi), development of allergies is a major limitation to its clinical use. Available pharmaceutical preparations of asparaginase vary in their pharmacokinetic and immunogenic properties.3-5E coli is the source of the most commonly used asparaginase preparation in the United States and is also widely used throughout the world. In the United States, Erwinia asparaginase is used only in patients who have an allergy to the E coli preparation. The reported frequency of antiasparaginase antibodies is highly variable; antibodies have been reported in as many as 79% of adults6 and as many as 70% of children7 after intravenous or intramuscular administration of E coli asparaginase. Antibody concentrations increase with repeated asparaginase administration and are higher in patients who exhibit overt allergic reactions.8 Development of antibodies may attenuate the antileukemic effect of asparaginase by shortening its half-life, preventing or delaying absorption after intramuscular injection, or interfering with enzyme activity.3,6,9 Clinical hypersensitivity reactions to E coli asparaginase are also common, and their reported frequency is highly variable (ranging from 0% to 45%).2,6,7,10-16 Factors that may affect the incidence of allergic reactions include different manufacturers, dosage, ongoing asparaginase administration, readministration after a hiatus, and concurrent chemotherapy.7,10,11,17-19 These reactions frequently require discontinuation of E coli asparaginase and subsequent substitution with another asparaginase preparation. The relationship between the development of antiasparaginase antibodies and allergic reactions and outcome in childhood acute lymphoblastic leukemia (ALL) has not been clearly defined. Recently, asparaginase allergy was found not to be prognostic among adults with ALL,20 although antibodies were not measured. In the current study, children were treated on a single protocol and had antiasparaginase antibody concentrations measured at a fixed time point relative to asparaginase dosing. Our objective was to determine whether the development of antiasparaginase plasma antibodies or clinical hypersensitivity reactions after intramuscular administration of E coli asparaginase had a significant impact on the event-free survival (EFS) of a group of uniformly treated children with newly diagnosed ALL.
Patient Eligibility and Treatment Schedules All 154 children with newly diagnosed ALL enrolled on St. Jude Children’s Research Hospital front-line protocol Total XIII-HR were evaluated. The criteria for eligibility, diagnosis, risk-group classification, and treatment have been reported elsewhere.21,22 Patients received E coli asparaginase (Elspar; Merck & Co, Inc, West Point, PA) 10,000 IU/m2 intramuscularly three times weekly for a total of nine doses during both induction and reinduction phases, as well as seven monthly doses during the first 7 months of continuation therapy. Two months after the last patient was accrued, the protocol was amended such that asparaginase doses 7, 8, and 9 during reinduction and all doses from maintenance were eliminated to reduce the risk of secondary acute myeloid leukemia (AML).21 In patients who developed clinical asparaginase allergy, patients were either premedicated with diphenhydramine, with or without glucocorticoids, or switched to a different preparation (Erwinia asparaginase or polyethylene glycol–conjugated [PEG] asparaginase), or both. The multiagent treatment regimen for Total XIII-HR is listed in Table 1. All allergic reactions were graded according to the standard National Cancer Institute common toxicity criteria. All treatment protocols were approved by the institutional review board, and informed consent was obtained from patients or their parents or guardians according to institutional guidelines.
Sample Collection For measurement of antiasparaginase antibodies, blood samples from a peripheral vein were collected in heparinized tubes on day 29 of induction therapy (ie, 10 days after nine doses of asparaginase) in 152 patients; two of 154 patients did not have plasma available for study for logistic reasons. Samples were centrifuged at 3,000 rpm for 5 minutes, and the plasma was stored at -70°C until analysis. Plasma or CSF suitable for asparagine measures was not available.
Determination of Antiasparaginase Antibodies
Statistical Methods EFS was measured from the date on which the patient was enrolled onto the study to the first failure of any kind (ie, relapse, secondary malignancy, or death) or the date of last follow-up. Patients who did not achieve a complete remission by day 43 were assigned an EFS value of zero. Distributions of EFS were estimated by the method of Kaplan and Meier,23 and associated SEs were calculated according to the method of Peto et al.24 Distributions of EFS were compared using the Mantel-Haenszel test stratified for immunophenotype, age at diagnosis, and WBC count at diagnosis. Logistic regression was used to test for relationships between explanatory variables of interest and whether patients experienced hypersensitivity. A Cox proportional hazards model, stratified for immunophenotype, age at diagnosis, and leukocyte count at diagnosis, was used to determine the impact of antiasparaginase plasma antibody concentration on EFS. No adjustments were made for multiple testing. All P values reported are two-sided, and all statistical analyses were conducted using SAS Release (Version 6.12, SAS Institute, Inc, Cary, NC).
Antiasparaginase Antibodies and Allergic Reactions Of the 154 patients, 151 achieved a complete remission. Antiasparaginase antibody concentrations were measured in 149 of the 151 patients who achieved remission and in the three who did not. Of the 152 children who had antibodies measured, 54 (35.5%) had detectable antibodies; all three children who did not achieve remission did not have detectable antibodies. Patient characteristics are listed in Table 2. Patients with B-lineage immunophenotype were more likely to develop antibodies than patients with T-lineage ALL (Table 2; P = .028). Patients who developed antibodies were more likely to experience a hypersensitivity reaction to asparaginase than those who did not (30 of 54 v 18 of 98; P < .001) (Fig 1). Among those who did develop antiasparaginase antibodies, the odds of experiencing a hypersensitivity reaction to asparaginase increased by approximately 5.6 times for each 0.01 OD increase in antibody concentration (P = .019). The proportion of children receiving the maximal number of asparaginase doses was not different in those who did versus those who did not exhibit antibodies (P = .31). The two patients who were not tested for antiasparaginase antibody experienced a hypersensitivity reaction.
Fifty (32.5%) of the 154 patients had one or more hypersensitivity reactions to E coli asparaginase, with initial reactions developing after three to 22 doses (median, 12 doses). The majority of hypersensitivity reactions to asparaginase occurred after the time point (day 29) at which antibody concentrations were measured. Six patients had nine reactions during induction; four of these patients had detectable antibodies at day 29, with two of the levels being among the highest antibody concentrations measured. In addition, there were 54 reactions during continuation and 26 reactions during reinduction therapy. Timing of initial (first) reactions were as follows: one patient each reacted to the third through seventh doses (one patient reacted to the fourth dose, but it was not given until continuation because of coagulopathy during induction), two reacted to the eighth dose, four reacted to the 10th dose, nine each reacted to the 11th and 12th doses, six reacted to the 13th dose, seven reacted to the 14th dose, three reacted to the 15th dose, and one each reacted to the 16th, 17th, 19th, 20th, and 22nd doses. After a reaction to asparaginase, patients either continued on the same preparation with premedication or switched to another asparaginase product (Fig 2).
Characteristics of the hypersensitivity reactions to asparaginase are listed in Table 3. Fifty patients experienced a total of 89 reactions to asparaginase (79 reactions to the E coli preparation and 10 to the Erwinia preparation). There was an approximately equal number of patients who presented with localized reactions alone and with generalized reactions alone; however, most reactions manifested as a plethora of symptoms rather than as single symptoms. One patient who exhibited a clinical allergic reaction to both E coli and Erwinia asparaginase received PEG asparaginase, a conjugate of the native E coli asparaginase covalently linked to polyethylene glycol, and reacted to this preparation with generalized erythema and angioedema.
EFS The 4-year EFS ± 1 SE for patients with and without antibodies was 83% ± 6% and 76% ± 5%, respectively (Fig 3). After stratifying for immunophenotype, age at diagnosis, and diagnostic WBC count, there was no evidence to suggest that the EFS of patients with antiasparaginase plasma antibodies was significantly different from that of those without antibodies (P = .54). Moreover, there was no evidence to suggest that antiasparaginase plasma antibody concentrations, evaluated as a continuous variable, had independent prognostic significance (P = .154).
The 4-year EFS ± 1 SE for patients who reacted to asparaginase and those who did not was 82% ± 6% and 78% ± 5%, respectively (Fig 4). After stratifying for immunophenotype, age at diagnosis, and diagnostic WBC count, there was no evidence to suggest that the EFS of patients who had hypersensitivity reactions to asparaginase was significantly different from that of those who did not (P = .68).
We observed no relationship between the development of antiasparaginase antibodies or hypersensitivity reactions and outcome in children with newly diagnosed ALL. Antibodies were measured at a fixed time point relative to asparaginase administration: day 29 of remission induction therapy after nine doses of intramuscular E coli asparaginase. Variables that may influence antibody levels and/or allergic reactions, such as previous exposure, time of treatment, and concurrent chemotherapy,4,7,10,11,18,19 were not confounding factors, because all patients were on the same treatment protocol. In this setting, in which asparagi- nase preparations were changed after reactions occurred, development of antiasparaginase antibodies at the end of remission induction or hypersensitivity reactions did not compromise EFS. Thirty-six percent of 152 patients, including 63% of the patients who exhibited clinical hypersensitivity, had measurable antibody levels. It has been suggested that antiasparaginase antibodies may have a deleterious effect on systemic exposure or effect of asparaginase, as development of antibodies has been associated with attenuated serum asparaginase activity in six of seven children and 15 of 16 adults.6 We did not measure asparaginase activity or asparagine concentrations in this study. However, it may be that the schedule of asparaginase was intense enough—either a high enough dose or a great enough frequency—such that attenuation of asparaginase by antibodies was not important with respect to outcome in these patients. Conflicting data exist regarding the relationship between antiasparaginase antibodies and clinical outcome, and studies have typically involved small numbers of patients and heterogeneous populations. In a study of children and adults with ALL and AML, the frequency of remission among antibody producers was 68% (13 of 19 patients) and among nonproducers was 27% (three of 11 patients).6 Antibody formation was hypothesized to be a surrogate for an active immune response against leukemic cells and thus a good prognostic factor. In contrast, Cheung et al10 found that six children who did not make appreciable amounts of antibody were in continuous marrow remission after 26 months, whereas four of seven patients who had higher levels of antibody experienced relapse and died. These investigators hypothesized that asparaginase inactivation by antibodies had occurred and was deleterious in their patients. In our large cohort of patients who received uniform therapy for the same disease, we found no significant differences in EFS between patients who developed antibodies at the end of remission induction and those who did not. It has been proposed that hypersensitivity to asparaginase may attenuate its pharmacologic effect. Asselin et al3 were unable to detect asparaginase activity 1 week after a reaction to E coli asparaginase in 80% of patients who continued to receive the same preparation, and the enzyme half-life was significantly shorter in patients who were switched to PEG asparaginase (mean ± SD, 1.82 ± 0.26 days) than in those who never had a reaction (5.73 ± 3.24 days; P < .01). Furthermore, Gentili et al25 reported that no patient who reacted to Erwinia asparaginase experienced plasma asparagine depletion. Despite prior reports of the effect of hypersensitivity reactions on asparaginase pharmacokinetics and pharmacodynamics, we found no significant differences in EFS between patients who reacted to asparaginase and those who did not. Adverse consequences of hypersensitivity in our study may have been minimized, as patients who had a hypersensitivity reaction to E coli were quickly switched to the Erwinia preparation and did not receive fewer total doses of asparaginase. Consistent with our finding, in a study of adults with newly diagnosed ALL, even patients who had hypersensitivity reactions requiring discontinuation of asparaginase did not have a shorter remission duration than did patients who received all planned doses.20 Thirty-three percent of the 154 children included in this study had a hypersensitivity reaction to asparaginase, which is consistent with the reported frequency in children (0% to 45%).5,6,10-12,14,17,18,26-28 The majority of the reactions occurred during the continuation phase (54 reactions v nine during induction and 26 during reinduction therapies), which may be related to the monthly administration schedule, as the risk of hypersensitivity reactions may increase with readministration after a period of no asparaginase therapy for at least a month.17 Also, the reduced incidence of allergic reactions during induction and reinduction may be caused by immunosuppression associated with concomitant chemotherapy,10,11,17-19 particularly glucocorticoids. Fourteen percent of patients who reacted to E coli asparaginase eventually reacted to Erwinia asparaginase, which is similar to results from previous reports.5,17,18,29,30 Patients generally reacted sooner to Erwinia asparaginase than they did to the E coli preparation, as initial reactions to E coli asparaginase occurred after a median of 12 doses (range, three to 22 doses), and subsequent reactions after Erwinia asparaginase occurred after a median of four doses (range, one to 11 doses). The rapid hypersensitivity may have been related to previous reactions to E coli asparaginase and the total number of asparaginase doses received, which are both risk factors for reactions to Erwinia asparaginase.17 Patients who developed antiasparaginase antibodies were more likely to experience a hypersensitivity reaction than those who did not. Furthermore, the risk of developing a hypersensitivity reaction among patients who developed antiasparaginase antibodies was related to the antibody concentration. In this subset of patients, 50% of patients who experienced an allergic reaction had an antibody concentration greater than an OD of 0.135 at 1:3200 dilution, whereas there were no patients who did not experience allergic reactions whose levels exceeded this value (data not shown). Although antiasparaginase antibodies were measured only on day 29 of induction and the majority of the hypersensitivity reactions occurred later, antibody analysis may be of clinical value, especially if patients are to receive multiple or additional courses of asparaginase treatment, because elevated antibody levels may indicate an increased risk of future hypersensitivity. We have also previously shown that antibody levels increase with the number of asparaginase doses, but the antiasparaginase antibody concentration at the end of induction and before any hypersensitivity reaction was higher in patients who experienced a subsequent reaction than in those who never experienced a reaction.8 Although drug hypersensitivity has most commonly been related to IgE, antibodies to asparaginase have been characterized as IgG.10 Cheung et al10 detected IgG antibodies in eight patients who experienced a hypersensitivity reaction (mean, 42 U/mL; range, 21 to 70 U/mL) after multiple doses of intramuscular or intravenous E coli asparaginase. In contrast, the 18 patients who did not have a reaction had a mean IgG antibody level of 6 U/mL (range, 2 to 12 U/mL). The eight patients with hypersensitivity reactions did not have a significantly different IgE level as compared with normal, unimmunized, nonallergic volunteers (mean ± SD, 77 ± 65 cpm v 65 ± 63 cpm, respectively). Thus in our study, we measured IgG antiasparaginase antibodies and not IgE antibodies. The use of asparaginase immediately before etoposide administration has been implicated in an increased rate of secondary AML; this is possibly the result of decreased synthesis of a protein that is required to repair DNA damage or reverse recombinogenesis induced by etoposide.21,31,32 In our study, there were nine patients whose first adverse event was secondary AML; five of the nine patients had detectable antibodies (median OD, 0.026; range, 0.00 to 0.133), and three developed allergic reactions. One additional patient initially experienced an isolated CNS relapse but was diagnosed with secondary AML approximately 1 year later. This patient did not develop detectable antibodies or experience hypersensitivity. In general, E coli asparaginase was well tolerated in these pediatric patients, and most patients received all of the planned therapy. Patients who had antiasparaginase antibodies or patients who had hypersensitivity reactions to E coli asparaginase did not have a significantly different EFS than the remaining children treated on this ALL protocol. It is possible that E coli asparaginase is inactivated in patients who develop antiasparaginase antibodies or become hypersensitive, but any adverse prognostic significance of such inactivation may have been attenuated in our patients because we substituted another asparaginase preparation. In addition, patients on this protocol received several addi- tional antileukemic agents during continuation treatment (etoposide, cyclophosphamide, methotrexate, mercaptopurine, prednisone, vincristine, and cytarabine); thus any attenuation of the asparaginase effect may have been obscured by the intensity of other active antileukemic agents.
Supported in part by the National Institutes of Health, Bethesda, MD; Cancer Center CORE grant nos. CA-21765 and CA-51001; a Center of Excellence Grant from the State of Tennessee; a grant from Rhône-Poulenc Rorer Pharmaceuticals Inc; and American Lebanese Syrian Associated Charities. We thank our nurses, Sheri Ring, Margaret Edwards, Terri Kuehner, and Lisa Walters, and Jean Cai, Ken Cox, Ya Qin Chu, Krystal Effinger, Sherree Johns, Natasha Lenchik, and Yi Su for their excellent technical assistance.
1. Capizzi RL, Bertino JR, Skeel RT, et al: L-asparaginase: Clinical, biochemical, pharmacological, and immunological studies. Ann Intern Med 74:893-901, 1971 2. Haskell CM, Canellos GP: l-asparaginase resistance in human leukemia–asparagine synthetase. Biochem Pharmacol 18:2578-2580, 1969[Medline]
3.
Asselin BL, Whitin JC, Coppola DJ, et al: Comparative pharmacokinetic studies of three asparaginase preparations. J Clin Oncol 11:1780-1786, 1993 4. Evans WE, Tsiatis A, Rivera G, et al: Anaphylactoid reactions to Escherichia coli and Erwinia asparaginase in children with leukemia and lymphoma. Cancer 49:1378-1383, 1982[Medline] 5. Billett AL, Carls A, Gelber RD, et al: Allergic reactions to Erwinia asparaginase in children with acute lymphoblastic leukemia who had previous allergic reactions to Escherichia coli asparaginase. Cancer 70:201-206, 1992[Medline] 6. Killander D, Dohlwitz A, Engstedt L, et al: Hypersensitive reactions and antibody formation during L-asparaginase treatment of children and adults with acute leukemia. Cancer 37:220-228, 1976[Medline] 7. Oettgen HF, Stephenson PA, Schwartz MK, et al: Toxicity of E. coli L-asparaginase in man. Cancer 25:253-278, 1970[Medline] 8. Woo MH, Hak LJ, Storm MC, et al: Anti-asparaginase antibodies following E. coli asparaginase therapy in pediatric acute lymphoblastic leukemia. Leukemia 12:1527-1533, 1998[Medline] 9. Peterson RG, Handschumacher RE, Mitchell MS: Immunological responses to L-asparaginase. J Clin Invest 50:1080-1090, 1971 10. Cheung NK, Chau IY, Coccia PF: Antibody response to Escherichia coli L-asparaginase. Prognostic significance and clinical utility of antibody measurement. Pediatr Hematol Oncol 8:99-104, 1986 11. Nesbit M, Chard R, Evans A, et al: Evaluation of intramuscular versus intravenous administration of L-asparaginase in childhood leukemia. Am J Pediatr Hematol Oncol 1:9-13, 1979[Medline] 12. Pratt CB, Simone JV, Zee P, et al: Comparison of daily versus weekly L-asparaginase for the treatment of childhood acute leukemia. J Pediatr 77:474-483, 1970[Medline]
13.
Pratt CB, Choi SI, Holton CP: Low-dosage asparaginase treatment of childhood acute lymphocytic leukemia. Am J Dis Child 121:406-409, 1971
14.
Jaffe N, Traggis D, Das L, et al: L-asparaginase in the treatment of neoplastic diseases in children. Cancer Res 31:942-949, 1971 15. Jaffe N, Traggis D, Das L, et al: Favorable remission induction rate with twice weekly doses of L-asparaginase. Res 33:1-4, 1973 16. Leventhal BG, Henderson ES: Therapy of acute leukemia with drug combinations which include asparaginase. Cancer 28:825-829, 1971[Medline] 17. Evans WE, Tsiatis A, Rivera G, et al: Anaphylactoid reactions to Escherichia coli and Erwinia asparaginase in children with leukemia and lymphoma. Cancer 49:1378-1383, 1982 18. Land VJ, Sutow WW, Fernbach DJ, et al: Toxicity of L-asparaginase in children with advanced leukemia. Cancer 30:339-347, 1972[Medline] 19. Jacquillat C, Weil M, Bussel A, et al: Treatment of acute leukemia with L-asparaginase: Preliminary results on 84 cases. Recent Results Cancer Res 33:263-278, 1970[Medline] 20. Larson RA, Fretzin MH, Dodge RK, et al: Hypersensitivity reactions to L-asparaginase do not impact on the remission duration of adults with acute lymphoblastic leukemia. Leukemia 12:660-665, 1998[Medline] 21. Pui C-H, Relling MV, Behm FG, et al: L-asparaginase may potentiate the leukemogenic effect of the epipodophyllotoxins. Leukemia 9:1680-1684, 1995[Medline] 22. Relling MV, Yanishevski Y, Nemec J, et al: Etoposide and antimetabolite pharmacology in patients who develop secondary acute myeloid leukemia. Leukemia 12:346-352, 1998[Medline] 23. Kaplan EL, Meier P: Nonparametric estimation from incomplete observations. J Am Stat Assoc 53:457-481, 1958 24. Peto R, Pike MC, Armitage P, et al: Design and analysis of randomized clinical trials requiring prolonged observation of each patient: II. Analysis and examples. Br J Cancer 35:1-39, 1977[Medline]
25.
Gentili D, Conter V, Rizzari C, et al: L-asparagine depletion in plasma and cerebrospinal fluid of children with acute lymphoblastic leukemia during subsequent exposures to Erwinia L-asparaginase. Ann Oncol 7:725-730, 1996 26. Dellinger CT, Miale TD: Comparison of anaphylactic reactions to asparaginase derived from Escherichia coli and from Erwinia cultures. Cancer 38:1843-1846, 1976[Medline] 27. Steuber CP, Levy GJ, Nix WL, et al: Use of L-asparaginase and cytosine arabinoside for refractory acute lymphocytic leukemia with particular reference to T-cell leukemia. Med Pediatr Oncol 5:33-38, 1978[Medline]
28.
Ertel IJ, Nesbit ME, Hammond D, et al: Effective dose of L-asparaginase for induction of remission in previously treated children with acute lymphocytic leukemia: A report from Childrens Cancer Study Group. Cancer Res 39:3893-3896, 1979 29. Ohnuma T, Holland JF, Meyer P: Erwinia carotovora asparaginase in patients with prior anaphylaxis to asparaginase from E. coli. Cancer 30:376-381, 1972[Medline] 30. King OY, Wilbur JR, Mumford DM, et al: Therapy with Erwinia L-asparaginase in children with acute leukemia after anaphylaxis to E. coli L-asparaginase. Cancer 33:611-614, 1974[Medline] 31. Pui C-H, Relling MV, Rivera GK, et al: Epipodophyllotoxin-related acute myeloid leukemia: A study of 35 cases. Leukemia 9:1990-1996, 1995[Medline]
32.
Winick NJ, McKenna RW, Shuster JJ, et al: Secondary acute myeloid leukemia in children with acute lymphoblastic leukemia treated with etoposide. J Clin Oncol 11:209-217, 1993 Submitted August 26, 1999; accepted November 17, 1999.
This article has been cited by other articles:
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|||||||||||
|
|||||||||||
|
|
Copyright © 2000 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
|
TOP
ABSTRACT
INTRODUCTION
0.016 (mean OD of 20 untreated normal human volunteers + 2 SDs) at 1:3200 plasma dilution were considered to be positive for antibodies. 
2 test were used to determine whether or not categorical variables of interest differed in their distributions between two groups. The Wilcoxon rank sum test was used to compare continuous variables. 
