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We conducted a clinical trial to test whether prophylactic cranial irradiation could be omitted in all children with newly diagnosed acute lymphoblastic leukemia.
A total of 498 evaluable patients were enrolled. Treatment intensity was based on presenting features and the level of minimal residual disease after remission induction treatment. Continuous complete remission was compared between the 71 patients who previously would have received prophylactic cranial irradiation and the 56 historical controls who received it.
The 5-year event-free and overall survival probabilities (95% confidence interval) for all 498 patients were 85.6% (79.9% to 91.3%) and 93.5% (89.8% to 97.2%), respectively. The 5-year cumulative risk of isolated central-nervous-system (CNS) relapse was 2.7% (1.1% to 4.2%), and that of any CNS relapse (isolated plus combined) was 3.9% (1.9% to 5.9%). The 71 patients had significantly better continuous complete remission than the 56 historical controls (P=0.04). All 11 patients with isolated CNS relapse remain in second remission for 0.4 to 5.5 years. CNS leukemia (CNS-3 status) or a traumatic lumbar puncture with blasts at diagnosis and a high level of minimal residual disease (≥ 1%) after 6 weeks of remission induction were significantly associated with poorer event-free survival. Risk factors for CNS relapse included the presence of the t(1;19)[TCF3-PBX1], any CNS involvement at diagnosis, and T-cell immunophenotype. Common adverse effects included allergic reactions to L-asparaginase, osteonecrosis, thrombosis, and disseminated fungal infection.
With effective risk-adjusted chemotherapy, prophylactic cranial irradiation can be safely omitted in the treatment of childhood acute lymphoblastic leukemia.
Contemporary clinical trials have yielded 5-year event-free survival rates of 79% to 82% for children with acute lymphoblastic leukemia (ALL).1–3 A major challenge is to reduce treatment-related late effects that may occur in more than two-thirds of long-term survivors.4 For a growing proportion of patients, prophylactic cranial irradiation, once a standard treatment, is being replaced by intrathecal and systemic chemotherapy to reduce radiation-associated late complications, such as second cancers, neurocognitive deficits, and endocrinopathy.4–8
Two pediatric clinical trials tested whether prophylactic cranial irradiation could be completely omitted.9,10 Although the cumulative risks of isolated central-nervous-system (CNS) relapse in these trials were relatively low (4% and 3%), event-free survival rates were only 68.4% and 60.7%, respectively. In another study, prophylactic cranial irradiation appeared to improve outcome of children with T-cell ALL.11 Thus, there is a persistent concern that residual leukemic cells remaining after inadequate CNS treatment could not only cause CNS relapse but also reseed bone marrow, leading to hematologic relapse. Thus, virtually all study groups continue to use prophylactic cranial irradiation for up to 20% of patients.12
In our Total XIIIA study, 22% of the patients received prophylactic cranial irradiation, overall 5-year event-free survival rate was 77.6%, and cumulative risk of isolated CNS relapse was 1.2%.13 We substituted prednisone with dexamethasone in post-remission therapy and limited prophylactic cranial irradiation to 12% of the patients in the subsequent Total XIIIB study, resulting in a 5-year event-free survival of 80.8% and a cumulative risk of an isolated CNS relapse of 1.7%.3 In the Total XV study reported here, we tested whether intensification of systemic drugs that affect CNS control, together with optimal intrathecal treatment, would allow the complete omission of prophylactic cranial irradiation without compromising overall survival. These modifications were made in the context of risk assignment based on sequential measurements of minimal residual disease (MRD), and adjustment of chemotherapy dosages based on pharmacogenetics and pharmacokinetics.
From June 2000 to October 2007, 501 consecutive patients (1 to 18 years old) with newly diagnosed ALL were enrolled in Total XV Study at St. Jude Children’s Research Hospital (n=411) or at Cook Children’s Medical Center (n=90). Three patients were subsequently excluded because of a revised diagnosis of myeloid leukemia. The protocol was approved by the institutional review boards and registered at ClinicalTrials.gov, number NCT00137111. Signed informed consent was obtained from the parents or guardians, with assent from the patients, as appropriate.
The diagnostic criteria of ALL was described previously.14 CNS status was defined as CNS-1, CNS-2, CNS-3, or traumatic lumbar puncture with blasts.12 MRD was determined by flow cytometry and/or polymerase-chain-reaction.15,16
Our major therapeutic aims were (i) to determine whether prophylactic cranial irradiation can be safely omitted in all patients, especially those who would have received this treatment at approximately 1 year of continuous complete remission based on previous criteria (presenting leukocyte count ≥ 100 × 109/L, Philadelphia chromosome, CNS-3 status, or T-cell ALL with leukocyte count ≥ 50 × 109/L),3,13 and (ii) to estimate the overall event-free survival. The study was monitored by an independent Data Safety Monitoring Board. Group-sequential designs were used to provide guidelines for stopping decisions based on safety and efficacy (See Supplementary Appendix for details).
Risk classification was based on presenting features and treatment response. B-cell precursor cases with age between 1 and 10 years and leukocyte count <50 × 109/L, DNA index ≥ 1.16, or t(12;21)[ETV6-RUNX1] were provisionally classified as low-risk ALL. Cases with t(9;22)[BCR-ABL1] were considered to have high-risk ALL, while the remaining cases were provisionally classified as standard (intermediate)-risk ALL. The final risk status was determined by MRD levels. Any patient with ≥ 1% bone marrow MRD on day 19 of remission induction, or 0.1% to 0.99% MRD after completion of 6-week induction therapy was considered to have standard-risk ALL. MRD ≥ 1% after completion of induction therapy denoted high-risk ALL.
Patients who consented to the optional therapeutic window were randomized to receive upfront methotrexate over 4 or 24 hours. Four days after methotrexate treatment, remission induction therapy began with prednisone, vincristine, daunorubicin, and asparaginase (Table 1). Patients with ≥ 1% MRD on day 19 received three additional doses of asparaginase. Subsequent induction therapy consisted of cyclophosphamide, mercaptopurine and cytarabine. Upon hematopoietic recovery (between days 43 and 46), MRD was assessed, and consolidation therapy began (Table 1).
During initial continuation therapy (Table 1), low-risk cases received daily mercaptopurine and weekly methotrexate with pulses of mercaptopurine, dexamethasone and vincristine. Two reinduction treatments were given between weeks 7–9 and weeks 17–19. Standard-risk cases received weekly asparaginase and daily mercaptopurine with pulses of doxorubicin plus vincristine plus dexamethasone. They also received two reinduction treatments between weeks 7–9 and weeks 17–20.
For the remaining continuation therapy (Supplementary Table 1), low-risk patients received mercaptopurine and methotrexate, with pulses of dexamethasone, vincristine and mercaptopurine, and standard-risk patients received three rotating drug pairs (mercaptopurine plus methotrexate, cyclophosphamide plus cytarabine, and dexamethasone plus vincristine). Dosages of mercaptopurine and methotrexate were adjusted according to the tolerance, and thiopurine methyltransferase phenotype and genotypes.17 Total scheduled dosages of anthracyclines and cyclophosphamide were limited to 110 mg/m2 and 230 mg/m2, and 1 g/m2 and 4.6 g/m2, for low-risk and standard-risk patients, respectively. Continuation treatment lasted 120 weeks in girls and 146 weeks in boys.
Intrathecal cytarabine was instilled following diagnostic lumbar puncture and triple intrathecal chemotherapy was given for all subsequent treatments (Table 1). Depending on the presenting features and the CNS status, low-risk patients received 13 to 18, and standard-risk patients 16 to 25, intrathecal treatments.
This procedure was an option for patients with high-risk leukemia (whose early treatment was identical to that for standard-risk patients). Reintensification therapy (Supplementary Table 2) was given to maximize MRD reduction before transplantation. The median time to transplantation after remission induction was 4.1 months (range, 2 to 12 months).
All analyses were pre-specified in the protocol. To assess the effect of omitting prophylactic cranial irradiation, we compared the continuous complete remission rate after 1 year of continuation therapy of the subset of patients who met our previous criteria for prophylactic cranial irradiation at 1 year to that of historical controls who received irradiation,3,13 using an unstratified Mantel-Haenszel test.
Event-free survival and overall survival distributions were compared with the Mantel-Haenszel test. The Cox proportional hazards model was used to identify independent prognostic factors without using any variable selection methods. The cumulative incidence of isolated CNS or any CNS relapse (isolated plus combined), as well as other adverse events, were constructed by the method of Kalbfleisch and Prentice, and compared using Gray’s test. Fine and Gray’s model and the weighted logistic regression model18 were used to identify independent factors for prognosis and toxicities, respectively.
The database on January 5, 2009 was used for analysis; 97% of the survivors had been seen within 1 year. The median follow-up time was 4.0 years (range, 1.2 to 8.4 years). All reported P-values are 2-sided and not adjusted for multiple tests.
Presenting characteristics of the 498 evaluable patients are summarized in Table 2. Median age at diagnosis was 5.3 years (range, 1.0 to 18.9 years) and median leukocyte count was 11.7 × 109/L (range, 0.4 to 1014 × 109/L). We had increased proportions of T-cell ALL (15.3%) or t(1;19)[TCF3-PBX1] (5.8%) cases, owing to the overrepresentation of African-American patients relative to other series.19 Based on MRD measurements successfully done on all patients, we reclassified the risk status of 58 patients: 30 from low to standard, 6 from low to high, and 22 from standard to high.
Outcomes were similar for patients treated in the two centers. Of the 498 patients, 492 (98.8%) entered complete remission (low-risk, 99.6%; standard-risk, 99.5%, and high-risk, 90.4%). Induction failures were due to 2 fatal infections and 4 refractory leukemias. Three of the latter four patients remain in remission for 4.6, 4.6 and 6.1 years after allogeneic transplantation.
Thirty-three patients underwent allogeneic transplantation (9 from matched-sibling, 17 matched-unrelated and 7 haploidentical donors) 2 to 12 months after remission induction (median, 4.1 months). Transplantation was performed in 6 patients for t(9;22)[BCR-ABL1] ALL, 21 for MRD ≥ 1% at the end of induction, 5 for persistent MRD on week 16 post-remission and 1 for near-haploidy. Twenty-four patients remain alive in remission, 7 died of complications, and 2 relapsed.
There were 17 hematologic, 11 isolated CNS, 4 combined CNS and hematologic, and 1 testicular relapses, 1 secondary myelodysplastic syndrome, and 12 deaths in remission (including those after transplantation). The 5-year cumulative risk (95% confidence interval) of isolated CNS relapse was 2.7% (1.1% to 4.3%), any CNS relapse was 3.9% (1.9% to 5.9%) (Fig.1), and any relapse was 9.3% (6.0% to 12.6%). Pertinent features of the 11 patients with isolated CNS relapse are summarized in Supplementary Table 3. Notably, all 11 patients remain alive in second remission for 0.4 to 5.5 years (median, 2.5 years); 10 have been off therapy (3 after transplantation) for 1 month to 4.1 years (median, 2.0 years). The 5-year event-free survival and overall survival estimates were 85.6% (79.9% to 91.3%) and 93.5% (89.8% to 97.2%) for all 498 patients (Fig. 1). All 30 low-risk patients reclassified into the standard-risk group remain free of relapse.
Among the 71 patients who met our previous criteria for receiving prophylactic CNS irradiation, two had bone marrow relapse, one CNS relapse, and one remission death. Their continuous complete remission after 1 year of continuation therapy was significantly better than that of the 56 historical controls (P=0.04):3,13 the 5-year rate was 90.8% (76% to 100%) versus 73.0% (61.2% to 84.8%) (Supplementary Fig. 1); the relative risk was 0.34 (0.11 to 1.02).
Table 2 shows treatment outcome by selected features. Only CNS-3 status or traumatic lumbar puncture with blasts and MRD ≥ 1% at the end of induction were independently associated with poorer event-free survival (Table 3). Features independently associated with isolated CNS relapse included T-cell ALL, African-American race, the t(1;19)[TCF3-PBX1] and any CNS involvement (Table 3).
Table 4 summarizes the most relevant toxicities. The cumulative risk of toxic death during chemotherapy was 1.4% (0.4% to 2.4%). T-cell cases had a higher risk of seizures than B-cell precursor cases. Osteonecrosis, thrombosis and hyperglycemia occurred more often in the standard- and high-risk arms, which featured higher doses of dexamethasone and asparaginase, than in the low-risk arm. Age >10 years was independently associated with an increased risk of severe infections, osteonecrosis, hyperglycemia, and thrombosis.
Total XV study achieved a 5-year survival rate of 93.5%, which is superior to results of all major studies reported to date.1–3,13,20–27 This outcome also compares favorably with the recent result (87.5%) reported by the Surveillance, End Results, and Epidemiology Program for patients less than 15 years old treated between 2000 and 2004.28 The 5-year survival rates of 97.7% for low-risk and 89.7% for standard-risk B-cell precursor ALL were especially gratifying. Importantly, our study demonstrated that with intensification of systemic and intrathecal chemotherapy, prophylactic cranial irradiation can be totally omitted without compromising overall survival. Indeed, the 71 patients who met previous criteria to receive prophylactic cranial irradiation fared significantly better than the 56 historical controls.3,13 Because etoposide and irradiation were given only to the small subgroup of patients who underwent transplantation, we expect a very low rate of therapy-induced cancers. Extrapolating from the long-term results of reported studies,1–3,20–26 we predict that no more than 4% of patients might develop major adverse events 5 to 10 years after diagnosis, and this treatment protocol should yield a 10-year survival rate, and perhaps a cure rate, of 90%.5
We attribute this improved outcome to the incorporation of effective treatment components from earlier clinical trials1–3,13,20–26 coupled with a stringent risk classification based on MRD and dose adjustments based on the pharmacogenetic and pharmacodynamic characteristics. We used increased dosage of methotrexate in T-cell or t(1;19)[TCF3-PBX1] ALL because these blasts accumulate methotrexate polyglutamates less avidly than blasts of other subtypes.29 Indeed, high-dose methotrexate has improved outcome in T-cell ALL,30 whereas relatively lower doses appear adequate for low-risk B-cell precursor ALL.31 We targeted methotrexate dose individually, a strategy that improved outcome in our previous trial,31 and used two courses of reinduction treatment which have been shown to benefit patients with intermediate-risk ALL.32
Intensified asparaginase treatment was used because this approach has improved outcome in previous trials.2,33 For patients with hypersensitivity reactions to native E coli asparaginase, Erwinia asparaginase was substituted at high and frequent doses because an inadequate dose of this drug led to inferior outcome.34 Because we used a relatively high dose of mercaptopurine, we prospectively identified patients with inherited deficiency of thiopurine-S-methyltransferase and lowered mercaptopurine dosage accordingly to avoid toxicities.17 We regularly monitored levels of thioguanine nucleotides to assess mercaptopurine treatment and administered methotrexate intravenously to ensure compliance. Dosages of mercaptopurine and methotrexate were adjusted to the limits of tolerance but not overzealously to avoid undue interruptions of therapy.27,35 Dexamethasone was used post-remission because it has yielded better outcome than prednisone or prednisolone.36,37
We relied on high-dose methotrexate, intensive asparaginase, dexamethasone, and optimal intrathecal therapy to control CNS leukemia. Intrathecal therapy was intensified in patients with blasts in the CSF, even from traumatic lumbar puncture, which has been associated with poor outcome, 38–41 Special precautions12 were taken to decrease the rate of traumatic lumbar punctures from 24% in previous studies42 to 8% in this study. We gave intrathecal therapy in a large volume (8 mL or more, depending on age), and kept patients in the prone position for at least 60 minutes after intrathecal therapy,12 which improves intraventricular distribution.43,44 Finally, we used triple intrathecal therapy, which proved more effective than intrathecal methotrexate for CNS control.45 With these measures, the isolated CNS relapse rate was 2.7%, well within the 1.5% to 4.5% range in clinical trials that used prophylactic cranial irradiation.1–3,13,20–26,37 Only 1 of our 9 patients with CNS-3 status developed CNS relapse. Although a remarkably low rate (0.6%) of isolated CNS relapse was achieved in one study, approximately two-thirds of those patients received cranial irradiation.2
Our improved therapy has abolished most historically important prognostic factors, including leukocyte count. Even though high levels of MRD (i.e., ≥ 1%) at the end of induction were still associated with a poor outcome, use of this measure for risk-directed therapy has undoubtedly contributed to the improved results in this study. Indeed, while patients with MRD levels between 0.01% and 0.99% had a cumulative risk of relapse of 43% in our previous trials,15 those with the same levels had a 5-year event-free survival rate of 79.5% in this study. Despite intensive treatment, vigilant supportive care resulted in a toxic death rate of only 1.4%. Rates of disseminated fungal infection and thrombosis were relatively high but no patient died of these complications. Children over 10 years of age were more likely than younger patients to develop severe infection, osteonecrosis, thrombosis, and hyperglycemia, a finding that may be explained by slower clearance of dexamethasone in older patients.46
The complete omission of prophylactic cranial irradiation allowed us to clearly identify risk factors for CNS relapse: any CNS involvement, the t(1;19)[TCF3-PBX1] and T-cell ALL. We would argue against using prophylactic cranial irradiation even in patients with these features because approximately 90% would have received unnecessary irradiation. Further, since CNS and hematologic relapses are competing events, eradication of occult CNS leukemia by cranial irradiation alone may allow overt systemic relapse from residual leukemia in the bone marrow or other sites, which is more difficult to salvage. Indeed, in one study, triple intrathecal treatment reduced the frequency of CNS relapse compared with intrathecal methotrexate, but was associated with increased bone marrow and testicular relapse rates, leading to a poor overall survival.45 Moreover, patients with isolated CNS relapse who have not received prophylactic irradiation are highly curable, especially if their bone marrow is not involved, as assessed by MRD determination.47,48 In this regard, all of our 11 patients with an isolated CNS relapse remain in second remission, and most are likely cured after one course of therapeutic irradiation. For patients at high risk of CNS relapse, we have further intensified early intrathecal treatments in our ongoing clinical trial.
This work was supported by grants (CA21765, CA51001, CA60419, CA78224, CA36401, and GM61393) from the National Institutes of Health, by American Cancer Society F.M. Kirby Clinical Research Professorship, and by the American Lebanese Syrian Associated Charities (ALSAC).
We are indebted to Julie Groff for assistance with the figure, Jeana Cromer, Emily Baum and Linda Holloway for data management, Dr. Sheila Shurtleff for molecular analysis, our clinical and laboratory colleagues, and many patients and parents who participated in the research program.
Dr. Pui reports receiving lecture fees from Enzon Pharmaceuticals; Dr. Cheng, receiving consulting fees and grant support from Enzon Pharmaceuticals, Dr. Jeha, receiving research support from Genzyme, Sanofi-Aventis, and EUSA Pharma; Dr. Downing, relationship with the American Society for Investigative Pathology as a Council Member; and Dr. Relling, research support from Enzon Pharmaceutical and consulting fees from Genome Explorations. No other potential conflict of interest relevant to this article was reported.