Acute lymphoblastic leukemia relapsing after first-line pediatric-inspired therapy: a retrospective GRAALL study

The outcome of adult patients with Philadelphia chromosome-negative acute lymphoblastic leukemia (Ph− ALL) relapsing after pediatric-inspired front-line therapy is ill known. Here 229 relapsing Ph− ALL younger adults (18–63 years) treated within the Group for Research on Adult Acute Lymphoblastic Leukemia (GRAALL)-2003/-2005 trials were considered. Salvage regimens consisted of potentially curative therapies in 194 cases, low-intensity therapies in 21, allogeneic stem cell transplant (allo-SCT) in 6 and best supportive care in 8. Overall, 77 patients received allo-SCT after relapse. The median follow-up was 3.1 years. A second complete remission (CR2) was achieved in 121 patients (53%). In multivariate analysis, only younger age <45 years (P=0.008) and CR1 duration ⩾18 months (P=0.009) predicted CR2. Overall survival (OS) at 2 and 5 years was 19.3% (14–24%) and 13.3% (8–18%), respectively. In CR2 patients, disease-free survival (DFS) at 2 and 5 years was 29.0% (21–38%) and 25% (17–33%). In multivariate analysis, CR1 duration ⩾18 months and allo-SCT after relapse were associated with longer DFS (P<0.009 and P=0.004, respectively) and longer OS (P=0.004 and P<0.0001, respectively). In conclusion, although younger adults relapsing after pediatric-inspired ALL therapies retain a poor outcome, some of them may be cured if CR1 duration ⩾18 months and if allo-SCT can be performed in CR2. New therapies are definitely needed for these patients.


INTRODUCTION
The prognosis of adult patients with relapsed Philadelphianegative (Ph − ) acute lymphoblastic leukemia (ALL) is dismal. [1][2][3][4][5] A frequent option in such circumstances is to obtain a new complete remission (CR) as a bridge to perform allogeneic stem cell transplantation (allo-SCT), which is the best prospect for cure. 5 This strategy mainly applies to younger and fit patients who can receive aggressive salvage regimens. Second CR (CR2) rates in such patients have been shown to range between 30 and 45% and median survival between 6 and 9 months only. [1][2][3][4][5][6][7] These data are mostly issued from studies incorporating patients treated before the era of pediatric-inspired strategies. The latter have yielded significant advances in this group of patients as demonstrated by the results of the two Group for Research on Adult Acute Lymphoblastic Leukemia (GRAALL)-2003 and -2005 trials. [8][9][10][11][12][13][14] The GRAALL-2005 trial only differed from the 2003 trial by the addition of a randomized evaluation of hyperfractionated cyclophosphamide during induction and late intensification and by the randomization of rituximab addition during all phases of therapy in CD20 + B-cell precursor (BCP) ALL patients. 14 High-risk patients 8,12 were candidate for allo-SCT in CR1.
The outcome of patients who relapsed after specific pediatriclike protocols in first-line therapy has to be further analyzed. The hypothesis was that as pediatric-based regimens have significantly improved survival, this might lead to a selection of patients with a more refractory disease/subclone. Here we retrospectively describe such results from a cohort of patients with relapsed Ph − ALL initially treated in the GRAALL-2003 and -2005 trials.

PATIENTS AND METHODS Patients
Between 2003 and 2011, 955 younger adults with de novo Ph − ALL aged between 15 and 59 years from 70 French, Belgian and Swiss centers were treated within the multicenter prospective French GRAALL-2003GRAALL- (N = 225, period: 2003GRAALL- -2005 and GRAALL-2005 (N = 730, period: 2006-2011) trials (clinicaltrials.gov, nos. NCT00222027 and NCT00327678, respectively). Of these 955 patients, 860 (548 BCP-ALL and 312 T-cell ALL (T-ALL)) reached CR1 and 311 further received allo-SCT in first CR (204 BCP-ALL and 107 T-ALL). 13 Overall, 264 patients (30%) relapsed, including 58 after allo-SCT. 1 For the purpose of this study, postrelapse information was collected retrospectively. First relapse and its issue was part of the information to be collected in the e-case report forms of the trials. Based on an extraction of these events, additional necessary information was retrieved from the patients' files.

Genetic/molecular status at diagnosis
Patients were assigned to risk groups according to definitions applied to previous GRAALL trials. 8,12 Some relapsed patients were informative for their genetic/molecular status at diagnosis according to data published by the GRAALL 11,12 MLL (KMT2A) gene rearrangements and IKZF1 gene deletion, for BCP-ALL, and NOTCH1/FBXW7/RAS/PTEN gene mutations/ deletions, for T-ALL, were thus considered as potential prognostic factors. There were no analyses of minimal residual disease levels in CR2 patients.

Statistical analyses
The primary objective of the study was to assess the outcome in younger Ph − ALL patients relapsing after having being treated in first-line therapy as part of the GRAALL-2003/-2005 trials. This was evaluated by assessing the CR2 rate as well as overall (OS) and disease-free survivals (DFS). Secondary objectives were to determine prognostic factors for CR2, DFS and OS.
CR2 was defined by a neutrophil count 41.0 × 10 9 /, a platelet count 4100 × 10 9 /l and bone marrow blasts o 5% while all extramedullary disease had resolved. Relapse after CR2 was defined as the reappearance of leukemic cells in the bone marrow or extramedullary. Patient characteristics and CR rates were compared using Fisher's exact test. Comparisons of medians were performed using the Mann-Whitney U-test.
OS was defined as the time from the day of first relapse to death or last follow-up. DFS was defined from the date of CR2 to that of second relapse or death or last follow-up. Survival outcomes were not censored at allo-SCT. OS and DFS were estimated using the Kaplan-Meier method and then compared using the log-rank test. 15 Characteristics considered for univariate analysis were age (⩽45 years), ALL lineage (B vs T), ALL risk classification (high vs standard), 8,12 CR1 duration (⩽18 months), prior allo-SCT, relapse type (central nervous system vs others), relapse treatment type (intensive vs non-intensive, allo-SCT after relapse or not) and response to salvage regimen (CR2 or not). To evaluate the prognostic value of CR2 achievement, a landmark period of 82 days (75th percentile of the achievement of CR2) was used. Some lineagespecific cytogenetic or molecular features present at diagnosis were also considered, including t(4;11)(q21;q23)/MLL-AF4(KMT2A-AFF1), low hypodiploidy/near triploidy and IKZF1 gene deletion for BCP-ALL and complex karyotype (⩾5 anomalies) or NOTCH1/FBXW7/RAS/PTEN mutational status for T-ALL.
Postrelapse allo-SCT was analyzed as a time-dependent event using Mantel-Byar estimations. 16 Factors associated with a P-value o 0.10 on univariate analysis were included in the final logistic regression hazard model for multivariate analysis. Multivariable regressions were performed with the Cox model. 17 Hazard ratios (HRs) are given with 95% confidence interval (CI).
STATA/SE 10.1 software (STATA, College Station, TX, USA) was used. All tests were two-sided, with a type I error at 5%.

Patients
Data were available for 229 of the 264 patients who relapsed after prior CR1 achievement. In this cohort, the median age at relapse was 35.7 years. Allo-SCT preceded relapse for 54 patients (24%) and the median duration of CR1 was 10 months (range, 0.5-74). One hundred and fifty-one patients (66%) had BCP-ALL and 165 patients (72%) carried high-risk characteristics 8,12 at diagnosis. The main site of relapse was bone marrow alone (n = 181, 79%). Characteristics of the patients are given in Table 1. Details of the patients' evolution are given in the flow chart ( Figure 1).

Salvage regimens
All salvage regimens were permitted after relapse and details are given in Table 2. Most patients (n = 194, 85%) were retreated intensively with a variety of reported regimens, 18-39 while 21 patients received less-intensive chemotherapy (mainly vincristine and corticosteroids), 6 upfront allo-SCT and 8 only best supportive care. The main novelties compared with previously reported salvage regimens were the use of second-generation purine analogs, such as clofarabine for BCP-ALL 18 (34 patients) or nelarabine for T-ALL 19 (12 patients), and a regimen based on L-asparaginase encapsulated in erythrocytes 21 (12 patients). Only a few patients received immunotherapy with rituximab 40 because of CD20 expression or gemtuzumab ozogamicin because of CD33 expression. 41 Only the 215 patients who received an intensive (frontline allo-SCT excluded) or a less-intensive salvage regimen were considered for the analysis of prognostic factors of CR2. Only the 108 patients having obtained CR2 after intensive salvage regimen were considered for DFS analyses, and only the 221 who had received a treatment at relapse were considered for OS analyses. In the univariate analysis, a younger age ( o 45 years; HR = 0.48 (95% CI, 0.27-0.87); P = 0.015) and a longer CR1 duration (418 months; HR = 0.45 (95% CI, 0.23-0.86); P = 0.017) were associated with CR2 achievement. In BCP-ALL, the presence of t(4;11) (n = 21) was also associated with failure to reach CR2 with only 20% of these patients reaching CR2.
The question remains of how to improve the results of these patients. Considering the factors predicting better OS, if we cannot influence such a parameter as CR1 duration, it remains that everything has probably still to be made to consider allo-SCT in all relapsing patients. The lower toxicity of RIC and the availability of alternative donors (cord blood or haplo-identical) may allow to proceed in time with allo-SCT for all these patients, even in case of comorbidities. However, it has to be recalled that patients who received allo-SCT after relapse in this series were in majority those who achieved CR2 (~80%) and that post-allo-SCT survival of patients with active disease at transplant (even if they finally achieved CR2) remains poor, 46,47 suggesting that upfront allo-SCT may not be an option in these circumstances. As a consequence, it appears crucial to obtain CR2, whatever the salvage regimen used, intensive or not. Interestingly, some prognostic genetic features observed at diagnosis, such as IKZF1 gene deletion or NOTCH1/ FBXW7/RAS/PTEN mutation status, were taken into account for their impact of postrelapse outcome. This has only been investigated in some pediatric publications. [48][49][50] None of these molecular features had any impact in terms of postrelapse outcome in our study, perhaps because of the small number of informative cases. It may also be, although this was not investigated, that different clones were involved at relapse which did not express mutations or deletions found at diagnosis. 50  Outcome of younger adults with relapsed Ph-negative ALL A Desjonquères et al Finally, the impact of minimal residual disease levels in adults reaching CR2 remains to be determined.The MRD level may help to discriminate patients who may benefit from additional therapy/ maintenance, such as blinatumomab, 51 before transplant.
In conclusion, younger adult patients relapsing after current ALL therapies still display a poor outcome. Yet, a minority of them may be cured, especially if CR1 duration has exceeded 18 months and if they are able to receive allo-SCT in CR2. New therapies have to be evaluated prospectively in these patients.