Historically, poor chromosomal morphology in ALL made banding studies challenging, and karyotypic abnormalities were not reliably detected in early studies.⁴² The implementation of modern metaphase spreading, banding, and molecular cytogenetic techniques now reveals prognostically significant abnormal karyotypes in the majority of adult patients with ALL.⁴³ These molecular techniques include fluorescent in situ hybridization using chromosome- and gene-specific probes for gene rearrangements that are difficult to identify, such as the t(12;21) chromosomal translocation.⁴⁴ Application of these sensitive methods has revealed, for instance, that the t(12;21) translocation is much less common in adults with ALL than in children.^45,46 Other age-related differences include fewer occurrences of numerical chromosome abnormalities and a higher incidence of the Ph chromosome in adults (Table 74.4).

Because of the profound prognostic implication of the Ph chromosome, molecular testing for the BCR–ABL gene rearrangement should be performed for all patients diagnosed with ALL. The Ph chromosome was originally identified in a patient with chronic myeloid leukemia (CML), in whom the BCR and ABL genes juxtaposed within the so-called major breakpoint region.²⁴ This transcribes a 7-kb messenger RNA that is expressed as a 210-kd fusion protein, or p210BCR-ABL. In ALL, a variant breakpoint location, which results in the smaller p190BCR-ABL oncoprotein, is commonly found.⁴⁷ A polymerase chain reaction (PCR) -based laboratory test capable of detecting both the p210BCR-ABL and p190^BCR-ABL gene transcripts is now readily available to most clinicians and should always be performed in all newly diagnosed patients.

The primary basis of initial treatment strategies for ALL depends on antigenic parameters, and, hence, all patients should have their leukemic blasts characterized by immunophenotypic analysis. By current World Health Organization classification, the majority of adult ALL cases involve the precursor lymphoid neoplasms.⁴⁸ Approximately 70% of cases are B-cell ALL, and 25% are T-cell ALL. The remaining 5% are a mature B-cell neoplasm, Burkitt leukemia.⁴⁹ Compared with adults, children less often present with T-lineage ALL. There is also a slightly higher incidence of myeloid antigen expression in adult ALL patients, with reported incidences ranging from 15% to 54% compared with 4% to 35% in children.^50,51 Commonly detected myeloid antigens include CD13, CD15, and CD33.

Rare cases with co-expression of multiple lymphoid and myeloid antigens may be considered acute biphenotypic leukemia according to criteria suggested by a European group.⁵² The clinical course appears to be poor; however, there is no uniform consensus on whether to manage these cases as acute myeloid or lymphoid leukemia.⁵³ The Royal Marsden Hospital group identified 25 acute biphenotypic leukemia patients whom they treated over a 7-year period.^54,55 The patients variably underwent remission induction with ALL-like regimens, AML-like regimens, or hybrid regimens containing elements of both with equal success, except for an excess of treatment-related mortality with the combined regimen. Overall survival was 39.4% at 2 years. They observed a high incidence of the Ph chromosome (41%) that partially accounted for the unfavorable outcome and emphasized the importance of aggressive risk-adapted therapy for these cases.

The major immunophenotypic subgroup with prognostic value and therapeutic importance is the mature B-cell neoplasm, Burkitt leukemia. Burkitt leukemia is characterized by strong expression of surface immunoglobulin in addition to other markers common to B-lineage ALL, including CD10, CD19, CD20, and CD22.⁵² These patients respond poorly to standard ALL therapy, and outcome was dismal until brief, dose-intensified treatment programs were established as standard therapy.^74,75,76 The substantial improvement in survival that resulted has negated the adverse prognostic value of this feature if patients are optimally managed.

T-cell ALL is another formerly unfavorable prognostic subgroup that, due to changes in treatment approach, is no longer a poor risk feature.⁷⁷ In fact, with many modern treatment programs, the T-cell immunophenotype has become prognostically favorable.^7,68,78 High WBC count does not adversely affect survival in T-cell ALL unless the WBC is >100 × 10⁹/L.^66,67,79 In addition, more detailed examination of prospective immunophenotypic data collected by the CALGB identified a subset characterized by expression of fewer than three T-cell markers that had an unfavorable prognosis.⁸⁰ Leukemic blasts from these patients also infrequently expressed mature T-cell surface markers such as CD1a, CD2, CD3, CD4, and CD8, and, hence, would be consistent with the “early” T-cell ALL immunophenotype also reported to be unfavorable by the GMALL.^81,82 The distinction between early T-ALL (sCD3-, CD1a-), thymic T-ALL (sCD3-/+, CD1a+), and mature T-ALL (sCD3+, CD1a-) described by GMALL may serve as an example of a clinically significant, risk-adapted treatment stratification.⁸³

Other immunophenotypic markers have variably been shown to have prognostic value but are less well established. CD34 is expressed more frequently in adults with B-lineage ALL and was reported to affect outcome by the CALGB adversely.⁸⁰ However, CD34 expression overlapped with both a high WBC and the presence of the Ph chromosome, and findings from other smaller series have yielded conflicting results.^{84, 85, 86, 87} and ⁸⁸ Expression of myeloid antigen markers was slightly more frequent in B-lineage ALL than in T-lineage ALL but had no prognostic value in either instance.⁶⁴,^80,89

Unfavorable cytogenetic abnormalities in adult ALL include t(9;22) [BCR-ABL], observed in up to 30% of cases, t(4;11)(q21;q23)[MLL-AFF1], rare in adult ALL, t(1;19)(q23;p13)[TCF3-PBX1], also rare, and a hypodiploid karyotype, seen in 5% to 6%. Translocations involving chromosomal band 14q11 and abnormalities of the short arm of chromosome 12, including t(12;21)[ETV6-RUNX1], observed in 3% of cases, are favorable cytogenetic abnormalities. Results from collaborative studies providing karyotypic data generally indicate disease-free survival rates less than 25% for
patients with unfavorable abnormalities, as opposed to greater than 75% for those with favorable cytogenetic findings.^{60,65,90, 91, 92, 93} and ⁹⁴ Additional reports from single institutions have provided similar outcome data.^95,96 Cytogenetic findings commonly identified in adult ALL with an intermediate prognosis include normal karyotype, hyperdiploidy, and abnormalities at 6q or 9p. The t(8;14) (q24;q32)[MYC-IGH] and other MYC gene rearrangements are associated with the Burkitt leukemia subtype and are not prognostically unfavorable markers with optimal treatment.

In the UKALL XII/ECOG 2993 trial, 41 patients (5%), without an established translocation, had a complex karyotype with 5 or more chromosomal abnormalities. Four patients were primary induction failures and 19 of 37 CR patients relapsed. All but 3 of these 19 patients relapsed within 2 years of diagnosis and 17 of the 19 died. EFS and OS were significantly inferior in this group. These results established complex karyotype as a poor prognostic indicator.⁹⁷

Adult Ph-positive patients achieve CR rates comparable to Ph-negative ALL patients, but the remissions are short and survival poor with standard therapy. The most frequent translocation in adults involving the MLL gene, located at chromosome band 11q23, is t(4;11) and is also associated with poor survival.⁹⁴ The t(1;19) translocation results in the TCF3–PBX gene rearrangement, and patients with this abnormality were found to have a 3-year disease-free survival rate of only 20%.⁹² Patients with hypodiploidy ranging from 30 to 39 chromosomes have a disease-free interval of only 2 to 4 months from the start of treatment.⁹²

Deletions and translocations involving 12p include the ETV6-RUNX1 gene rearrangement. ETV6 gene rearrangements are much less frequent in adults than in children but are prognostically favorable in both. Translocations involving the TCR-α/β loci at chromosome 14q11 most frequently result in rearrangement with the TLX1 (HOX1) gene at 10q24.⁹⁸ Adult ALL patients with t(10;14)(q24;q11) experience long survival, but this may reflect an association with T-cell ALL subtypes.^65,92

The absence of chromosomal abnormalities does not preclude the less conspicuous presence of aberrantly expressed oncogenes that promote leukemogenesis. Oligonucleotide microarrays, and more recently, next-generation sequencing technologies have led to a revolution in analysis of the leukemia genome and will undoubtedly add to cytogenetic profiling in the risk stratification of ALL. These are discussed in detail in Chapter 72. Using oligonucleotide microarrays, Ferrando et al. identified T-cell oncogenes—TLX1, TLX3, TAL1, and LYL1—that may have prognostic relevance in T-cell ALL.⁹⁹ These genes normally function as a homeobox gene (TLX1) or encode developmentally essential transcription factors (TAL1, LYL1) in normal thymocyte maturation. Their dysregulated expression is thought to foster leukemogenicity and can be detected as a signature genetic profile, which not only has the ability to provide insight into their pathogenetic heterogeneity, but also render important prognostic information. Overexpression of TLX1, present in approximately 30% of adult T-ALL cases, has been associated with a favorable prognosis, and in one study, demonstrated a leukemia-specific survival rate of 88% in TLX1-positive patients compared with 56% in TLX1-negative patients at a median follow-up of 4.7 years.¹⁰⁰ In contrast, the overexpression of TAL1 or LYL1 has been linked to poor response to treatment, and the predictive value of TLX3, another homeobox factor related to TLX1, is conflicting.^101,102

Another mechanism for ALL leukemogenesis is the constitutive activation of tyrosine kinase via the NUP214-ABL1 fusion episome. The juxtaposition of the two oncogenes leads to the familiar amplification of ABL1 on the chromosome band 9q34. However, the NUP214-ABL1 fusion escapes detection by conventional cytogenetics by virtue of its extrachromosomal position and requires molecular analysis for delineation. The fusion episome has been detected in approximately 6% of individuals with T-ALL.¹⁰³ Because of its sensitivity to abl tyrosine kinase inhibitors, the subset of T-ALL patients with this molecular feature is predicted to benefit from early identification.¹⁰⁴ The known presence of TLX1 or TLX3 may also merit exploration for the NUP214-ABL1 fusion given their tendency for co-expression.¹⁰⁵

Failure to achieve CR within 4 weeks of starting treatment or after one course of induction chemotherapy has been considered an independent unfavorable prognostic factor, confirmed in most adult ALL studies.^7,73 An exception is the international, multicenter UKALL XII/ECOG E2993 trial, which could not confirm its importance in its 1,500 patient cohort.⁶¹ When significant, early CR held predictive value for standard ALL programs as well as for newer, dose-intensified treatment protocols.^{5,67,78,106,107,108} Patients requiring greater than 4 weeks to achieve CR were at least twice as likely to relapse, depending on the study. In one study, patients who did not achieve CR by week 4 of induction had a 5-year disease-free survival of 0% as compared with 46% for the remainder of the complete responders.⁷⁸ In this study, the number of weeks required to achieve CR was only marginally worse than the Ph chromosome as an unfavorable variable.

Evaluation for persistence of leukemic blasts at even earlier time-points, between days 7 and 21 of induction, has been firmly established as an important prognostic indicator for outcome in pediatric ALL.^{109, 110} and ¹¹¹ Early persistence of leukemic blasts at 7 days after starting induction is thought to represent corticosteroid resistance.¹¹² In contrast, persistence at time-points after 21 days is considered a reflection of cytotoxic chemotherapy resistance. Numerous prospective studies in pediatric ALL have shown that a substantial unfavorable influence on outcome is associated with the morphologic detection of blood or marrow leukemic blasts persisting during induction therapy at day 7, day 21, or at other time-points in between. Persistence of leukemia was usually defined as the finding of greater than 1 × 10⁹/L blast cells in a peripheral blood sample or leukemic blasts greater than 5% of normal cells in a marrow specimen.

Although pediatric protocols already incorporate early treatment response assessment by a day 7 or day 14 bone marrow examination into risk classification, similar data in adult ALL are limited.¹¹³ Results from the few reported studies agree with findings from the pediatric experience. Sebban et al. prospectively evaluated persistence of marrow blasts, defined as greater than 5% of nucleated cells, at day 15 of induction for influence on outcome.¹⁰⁷ Among 437 adult ALL patients, one third were found
to have persistent blast cells. These patients were less likely to achieve CR after 4 weeks of therapy. Even among only the patients who achieved CR within 4 weeks, an otherwise favorable feature, those who had persistent blasts at day 15 fared significantly worse. Among all complete remitters, the 5-year disease-free survival was 34% for those who cleared marrow blasts at day 15, compared with 19% for those who did not. Annino et al. and the Italian collaborative study group evaluated the early corticosteroid response by giving a 7-day course of prednisone immediately before induction.⁹ The pre-induction response was previously shown to have strong prognostic value in pediatric ALL.^114,115 In the adult ALL study, prednisone response was defined by reduction of peripheral blood blasts to less than or equal to 1 × 10⁹/L. Lack of a prednisone response was found to affect overall survival negatively, as it did in the pediatric ALL studies, and, among CR patients, it also adversely influenced remission duration.

MRD refers to the post-remission persistence of leukemia that cannot be detected by histomorphologic assessment. Immunophenotypic, cytogenetic, or molecular techniques can be used to detect MRD.¹¹⁶ Samples from peripheral blood are generally one log10 less sensitive than bone marrow, perhaps as post-treatment BCR-ABL transcripts from peripheral blood clear more rapidly,¹¹⁷ but may have comparable sensitivity in T-lineage ALL.^118,119,120 Fluorescence in situ hybridization is better than conventional banding analysis for detecting chromosomal translocations and numerical abnormalities, but both techniques are limited by low sensitivity.^{121, 122, 123} and ¹²⁴ Flow cytometry, used in four or more color combinations and taking advantage of new reagents, detects aberrant antigen expression on leukemic cells and can unambiguously distinguish one leukemic blast among more than 104 normal cells in 90% of all patients.^125,126 This level of sensitivity is sufficient for prognostically significant MRD detection.¹²⁷ Additionally, flow cytometry is rapid, reliable, and allows accurate quantitation, and the technical requirements for the assay are already in place at most centers, making it an attractive diagnostic tool. The most sensitive assays for detecting MRD, however, are based on PCR techniques, which can detect one leukemic blast in up to 106 normal cells. PCR targets using fusion gene transcripts such as BCR-ABL, ETV6-RUNX1, AFF1–MLL, and E2A-PBX are relatively standardized, but each alone can only be used for patient subsets.^{128, 129} and ¹³⁰ PCR targets based on immunoglobulin and T-cell receptor gene rearrangements can be used to detect MRD in theoretically all patients, but lose sensitivity if consensus rather than patient-specific primers are used.^128,131 On the other hand, generating patient allele-specific primers requires DNA sequencing capability. Although a number of clinical studies have suggested the prognostic significance of threshold values of MRD,^132,133 early experience with accurate quantitation of leukemia-specific residual disease with the PCR assay was fraught with technical challenges, and standardization of assay sensitivity among testing facilities was of major concern.¹³⁰ Where available, however, real-time quantitative PCR technology utilizing newer automated methods has proven to be technically simple, yielding precise and consistent quantitation of residual leukemic clones, and is gaining widespread acceptance.^134,135 Information from pediatric ALL trials using PCR and flow cytometry in tandem may help determine more definitively the role of each for evaluating MRD.¹³⁶

The prognostic utility of MRD detection was first described in studies conducted on children with ALL.^109,128,137 Three of the pediatric studies stand out for having large patient numbers, inclusion of both B- and T-lineage ALL, and for including patients with poor risk features.^127,132,133 The European studies were multicentered and used PCR detection of patient-specific antigen receptor gene rearrangement, whereas Coustan-Smith et al. used multicolor flow cytometry in an unselected patient cohort treated at the St. Jude Children’s Research Hospital. MRD was determined at the end of induction and at various time-points thereafter. The testing was technically challenging, as 1,254 of 1,914 (66%) combined patients treated during the study period did not have suitable PCR targets, serial PCR performed, or an immunophenotype suitable for MRD assessment. Nonetheless, all three studies demonstrated an unfavorable influence of persistent MRD on relapse-free survival. By multivariate analyses in the St. Jude study, sequential detection of persistent MRD remained a poor prognostic marker after controlling for age, WBC count, and adverse cytogenetics including the Ph chromosome and MLL gene rearrangement.¹²⁷ Detection of MRD during maintenance therapy tended to have the strongest positive predictive value for relapse. Conversely, absence of MRD at the end of induction negated the unfavorable influence of persistent leukemic blasts at day 7 as a prognostic factor.

Studies assessing the predictive value of MRD in adult ALL have generally echoed findings of pediatric studies.^{138, 139} and ¹⁴⁰ Mortuza et al. reported results for 66 Ph-negative adult B-lineage ALL patients treated at a single institution, for whom MRD was assessed with PCR using consensus immunoglobulin heavy chain gene primers.¹³⁸ Detection of residual leukemia at the 10-3 level, the limit of sensitivity of the assay, independently correlated with inferior disease-free survival when measured 3 to 5 months after induction therapy. The kinetics of MRD clearance has also gained much attention with respect to predicting relapse risk. Among the 196 standard-risk ALL patients monitored by quantitative PCR during their first year of treatment in the German Multicenter Acute Lymphoblastic Leukemia (GMALL) study, the 3-year relapse rate was 0% if MRD declined rapidly to lower than 10^-4 at day 11, or below detection threshold at day 24, compared with a relapse rate of 94% if the MRD was at a level of 10^-4 or higher until week 16.¹⁴¹ Based on these results, they defined three risk groups based on MRD assessment in this otherwise homogeneous standard risk group. Scheuring et al. suggested that the magnitude and rate of BCR-ABL increase, as well as the absolute number of transcripts, could predict relapse within 2 months.¹⁴² Another large cooperative group study reported that a 2-log reduction of MRD after induction, and a greater than 3-log reduction after consolidation therapy were associated with a 2-year actuarial probability of overall, disease-free, and relapse-free survival of 48%, 27%, and 38%, respectively, compared with 0% survival with smaller reductions.¹⁴³ The increasingly recognized prognostic significance of MRD has prompted a large cooperative group study to evaluate prospectively the utility of MRD in selecting patients for stem cell transplantation in first CR as a model for risk-adapted treatment strategy.¹⁴⁴

Attention should be paid to metabolic, infectious, and hematologic issues before starting leukemia-specific therapy. Hyperuricemia, hyperphosphatemia, and secondary hypocalcemia may be pronounced with high leukemic cell burden and require intravenous hydration, alkalinization, and administration of allopurinol. In addition to myelosuppression during intensive treatment blocks, ALL therapy suppresses cell-mediated immunity, and some protocols have provisions for prophylaxis against herpes simplex virus and Pneumocystis jiroveci infections.¹⁰⁶ The clinical consequences of hyperleukocytosis (≥100 × 10⁹/L) in adult ALL patients are not well understood. Patients with MLL gene rearrangements and Burkitt leukemia are at higher risk for hyperleukocytosis at presentation.⁶⁰ In children, pronounced hyperleukocytosis involving lymphoid blasts are better tolerated than myeloid blasts, as reflected by fewer complications attributable to leukostasis or hemorrhage.¹⁴⁵ In one series, leukapheresis for pediatric ALL patients having blast counts greater than or equal to 2 × 10⁹/L led to outcomes equivalent to those for children who did not have this degree of hyperleukocytosis.¹⁴⁶ A similar policy is reasonable for adult ALL patients. Alternatively, immediate administration of prednisone or vincristine can rapidly reduce the circulating blast count. In an adult series, the WBC count dropped from greater than 100 × 10⁹/L to less than 1 × 10⁹ in 39% of patients given a 7-day course of prednisone immediately preceding remission induction chemotherapy.⁹

There are no useful clinical staging or prognostic scoring systems for adult ALL patients as there are for other hematologic malignancies, and there are no agreed-on uniform risk criteria as there are for pediatric ALL.^{147, 148, 149, 150} and ¹⁵¹ A prognostic model based on CALGB data suggested an additive effect of multiple adverse prognostic features on outcome, and, conversely, those without any poor prognostic factors did exceptionally well with few relapses.⁷ Others have described similar analyses.^66,78 Based on these models and the current clinical evidence, a general framework for risk assessment may consider placing adults with ALL in different risk prognostic categories (Fig. 74.3). All patients with at least one established poor prognosis factor based on clinical, immunophenotypic, cytogenetic, or molecular features and response to induction therapy should be considered at high risk for relapse. Adding response to therapy, based on MRD detection, as a risk criterion for adapting therapy has been validated in several adult studies. In two consecutive GMALL trials (GMALL 06/99 and 07/03) involving 1,648 patients, prospective MRD evaluation was used at several time-points. MRD absence after consolidation therapy was highly predictive of continuous complete remission after 5 years (74% vs. 35%) as well as OS (80% vs. 42%). A multivariate analysis of prognostic factors, including age, immunophenotype, risk group, and MRD status after consolidation, found that only the MRD status was predictive of CCR after 5 years with a hazard ratio of 4.5 (P < 0.0001). Both age, with a hazard ratio of 1.3 (P = 0.0007), and MRD status, with a hazard ratio of 4.0 (P < 0.0001), influenced overall survival.⁶²

In addition, patients with persistent MRD undergoing HSCT in first CR experienced higher rates of CCR than those without HSCT (66% vs. 11%), which led to better survival (54% vs. 32%). The Northern Italian Study Group also reported an advantage for patients positive for MRD treated with HSCT (n = 36) compared with non-HSCT (n = 18) with approximately 50% compared with 10% long-term disease-free survival.¹⁵²

The goal of remission induction therapy is hematologic complete remission (CR), as defined by the eradication of morphologically detectable leukemia cells in blood and bone marrow and the return of normal hematopoiesis. The importance of achieving CR after induction was highlighted in a study that demonstrated a 5-year overall survival rate of 45% in CR patients compared with 5% in patients who did not achieve CR.⁶¹ Remission induction chemotherapy for adults with ALL is most commonly built around a backbone of vincristine and prednisone. Remission induction with these two drugs in combination produces CR in approximately one half of patients with de novo ALL. The CR rate improves to 70% to 85% when an anthracycline is added, which was proven in a landmark CALGB trial to be superior to vincristine and prednisone alone.¹⁵³ Induction failures are evenly divided between refractory disease and toxicity-related mortality.^5,7,9,66,78 The efficacy of various anthracyclines in adults, including daunorubicin, doxorubicin, zorubicin, and mitoxantrone, has been similar.^{77,154, 155} and ¹⁵⁶

Many alterations to the basic induction regimen have been evaluated.^{82,157, 158, 159} and ¹⁶⁰ A critical evaluation of the individual merits of these modifications is challenging. Improvement to CR rates that already exceed 80% would be difficult to detect at a satisfactory level of significance. Modern treatment protocols are complex, and it is difficult to attribute outcome results to any one component or to make comparisons of significant findings between any two trials. For example, some modern induction protocols also incorporate L-asparaginase, cyclophosphamide, or both, although neither has been proven by controlled trials to be beneficial in adult ALL when added to standard three-drug induction regimens. The one randomized trial with L-asparaginase found no improvement in frequency or duration of CR with the addition of L-asparaginase to doxorubicin, vincristine, and prednisone during induction.¹⁶¹ Nonetheless, L-asparaginase has a mechanism of action that is close to being ALL-specific, causes minimal myelosuppression, and has been shown to be efficacious in pediatric ALL.¹⁶² An Italian Gruppo Italiano Malattie Ematologiche dell’ Adulto (GIMEMA) trial randomized adult ALL patients to induction with daunorubicin, vincristine, prednisone, and L-asparaginase with or without cyclophosphamide.⁹ The rate and durability of remission, as well as overall survival, did not differ between the two randomized treatment groups or for any subtype analyzed. In contrast, other studies have suggested a benefit with the inclusion of cyclophosphamide during induction, especially for patients with T-cell ALL, and, conversely, worse outcome with its omission.^7,163