Drug dosage and remission duration in childhood lymphocytic leukemia

Pharmacologic Inhibition of NT5C2 Reverses Genetic and Nongenetic Drivers of 6-MP Resistance in Acute Lymphoblastic Leukemia

Low-intensity maintenance therapy with 6-mercaptopurine (6-MP) limits the occurrence of acute lymphoblastic leukemia (ALL) relapse and is central to the success of multiagent chemotherapy protocols. Activating mutations in the 5'-nucleotidase cytosolic II (NT5C2) gene drive resistance to 6-MP in over 35% of early relapse ALL cases. Here we identify CRCD2 as a first-in-class small-molecule NT5C2 nucleotidase inhibitor broadly active against leukemias bearing highly prevalent relapse-associated mutant forms of NT5C2 in vitro and in vivo. Importantly, CRCD2 treatment also enhanced the cytotoxic activity of 6-MP in NT5C2 wild-type leukemias, leading to the identification of NT5C2 Ser502 phosphorylation as a novel NT5C2-mediated mechanism of 6-MP resistance in this disease. These results uncover an unanticipated role of nongenetic NT5C2 activation as a driver of 6-MP resistance in ALL and demonstrate the potential of NT5C2 inhibitor therapy for enhancing the efficacy of thiopurine maintenance therapy and overcoming resistance at relapse.

SIGNIFICANCE

Relapse-associated NT5C2 mutations directly contribute to relapse in ALL by driving resistance to chemotherapy with 6-MP. Pharmacologic inhibition of NT5C2 with CRCD2, a first-in-class nucleotidase inhibitor, enhances the cytotoxic effects of 6-MP and effectively reverses thiopurine resistance mediated by genetic and nongenetic mechanisms of NT5C2 activation in ALL. This article is highlighted in the In This Issue feature, p. 2483.

St. Jude Total Therapy studies from I to XVII for childhood acute lymphoblastic leukemia: a brief review

The therapy design of childhood acute lymphoblastic leukemia (ALL) has evolved over the past 60 years. The St. Jude Children's Research Hospital has developed 17 treatment protocols from 1962 to 2017, aiming to have the most effective and least toxic treatment form. This review summarizes each protocol's objectives, inclusion criteria, treatment phases, pharmacological agents, irradiation therapy, response criteria, risk stratification, type of relapse, and overall survival. The enhancement and successful application of preventive therapy for ALL and following a risk-stratified approach have progressively improved the cure rate of childhood ALL, with relatively few adverse sequelae. Moreover, St. Jude's scientific theme serves as a reminder of the principal factor of research directed to a catastrophic disease such as ALL.

Using Pharmacology to Squeeze the Life Out of Childhood Leukemia, and Potential Strategies to Achieve Breakthroughs in Medulloblastoma Treatment

Eliminating cancer was once thought of as a war. This analogy is still apt today; however, we now realize that cancer is a much more formidable enemy than scientists originally perceived, and in some cases, it harbors a profound ability to thwart our best efforts to defeat it. However, before we were aware of the complexity of cancer, chemotherapy against childhood acute lymphoblastic leukemia (ALL) was successful because it applied the principles of pharmacology. Herein, we provide a historic perspective of the experience at St. Jude Children's Research Hospital. In 1962, when the hospital opened, fewer than 3% of patients experienced durable cure. Through judicious application of pharmacologic principles (e.g., combination therapy with agents using different mechanisms of action) plus appropriate drug scheduling, dosing, and pharmacodynamics, the survival of patients with ALL now exceeds 90%. We contrast this approach to treating ALL with the contemporary approach to treating medulloblastoma, in which genetics and molecular signatures are being used to guide the development of more-efficacious treatment strategies with minimal toxicity. Finally, we highlight the emerging technologies that can sustain and propel the collaborative efforts to squeeze the life out of these cancers. SIGNIFICANCE STATEMENT: Up until the early 1960s, chemotherapy for childhood acute lymphoblastic leukemia was mostly ineffective. This changed with the knowledge and implementation of rational approaches to combination therapy. Although the therapeutics of brain cancers such as medulloblastoma are not as refined (in part because of the blood-brain barrier obstacle), recent extraordinary advances in knowledge of medulloblastoma pathobiology has led to innovations in disease classification accompanied with strategies to improve therapeutic outcomes. Undoubtedly, additional novel approaches, such as immunological therapeutics, will open new avenues to further the goal of taming cancer.

A New Hybrid δ-Lactone Induces Apoptosis and Potentiates Anticancer Activity of Taxol in HL-60 Human Leukemia Cells

In the search for new drug candidates, researchers turn to natural substances isolated from plants which may be either used directly or may serve as a source for chemical modifications. An interesting strategy in the design of novel anticancer agents is based on the conjugation of two or more biologically active structural motifs into one hybrid compound. In this study, we investigated the anticancer potential of 4-benzyl-5,7-dimethoxy-4-methyl-3-methylidene-3,4-dihydro-2H-chroman-2-one (DL-247), a new hybrid molecule combining a chroman-2-one skeleton with an exo-methylidene bond conjugated with a carbonyl group, in human myeloid leukemia HL-60 cell line. The cytotoxicity of the new compound was tested using MTT assay. The effect of DL-247 on cell proliferation and apoptosis induction were studied by flow cytometry, fluorometric assay and ELISA analysis. DL-247 displayed high cytotoxic activity (IC₅₀ = 1.15 µM, after 24 h incubation), significantly inhibited cell proliferation and induced apoptosis by both, the intrinsic and extrinsic pathways. A combination of DL-247 with taxol exhibited a strong synergistic effect on DNA damage generation, apoptosis induction and inhibition of cell growth.

Discontinuities and disruptions in drug dosage guidelines for the paediatric population

AIMS

This study investigates paediatric drug dosage guidelines with the aim of investigating their agreement with body surface area (BSA) scaling principles.

METHODS

A total of 454 drug dosage guidelines listed in the AMH-CDC 2015 were examined. Data extracted included the administration, frequency and dose per age bracket from 0 to 18 years. Drug treatments were categorized as follows: (1) The same dose recommendation in milligrams per kilogram (mg kg^-1 ) for all age/weights; (2) Change in the mg kg^-1 dosing according to age/weight; (3) Change in dose in mg according to age/weight; (4) Change from mg kg^-1 dosing to a dose in mg according to age/weight; (5) The same recommendation for all age/weight groups in mg; or (6) BSA dosing. Example drugs were selected to illustrate dose progression across ages.

RESULTS

Most drug treatments (63%) have the same mg kg^-1 dose for all age/weight groups, 14% are dosed in mg kg^-1 across all ages with dose changes according to age/weight, 13% were dosed in mg across all ages with dose changes, 10% switched from mg kg^-1 to a set dose in mg, 4.2% have the same dose in mg for all age and weight groups and 2.2% are dosed according to BSA.

CONCLUSIONS

Paediatric dosage guidelines are based on weight-based formulas, available dosing formulations and prior patterns of use. Substantial variation from doses predicted by BSA scaling are common, as are large shifts in recommended doses at age thresholds. Further research is required to determine if better outcomes could be achieved by adopting biologically based scaling of paediatric doses.

Inherited NUDT15 variant is a genetic determinant of mercaptopurine intolerance in children with acute lymphoblastic leukemia

PURPOSE

Mercaptopurine (MP) is the mainstay of curative therapy for acute lymphoblastic leukemia (ALL). We performed a genome-wide association study (GWAS) to identify comprehensively the genetic basis of MP intolerance in children with ALL.

PATIENTS AND METHODS

The discovery GWAS and replication cohorts included 657 and 371 children from two prospective clinical trials. MP dose intensity was a marker for drug tolerance and toxicities and was defined as prescribed dose divided by the planned protocol dose during maintenance therapy; its association with genotype was evaluated using a linear mixed-effects model.

RESULTS

MP dose intensity varied by race and ethnicity and was negatively correlated with East Asian genetic ancestry (P < .001). The GWAS revealed two genome-wide significant loci associated with dose intensity: rs1142345 in TPMT (Tyr240Cys, present in *3A and *3C variants; P = 8.6 × 10(-9)) and rs116855232 in NUDT15 (P = 8.8 × 10(-9)), with independent replication. Patients with TT genotype at rs116855232 were exquisitely sensitive to MP, with an average dose intensity of 8.3%, compared with those with TC and CC genotypes, who tolerated 63% and 83.5% of the planned dose, respectively. The NUDT15 variant was most common in East Asians and Hispanics, rare in Europeans, and not observed in Africans, contributing to ancestry-related differences in MP tolerance. Of children homozygous for either TPMT or NUDT15 variants or heterozygous for both, 100% required ≥ 50% MP dose reduction, compared with only 7.7% of others.

CONCLUSION

We describe a germline variant in NUDT15 strongly associated with MP intolerance in childhood ALL, which may have implications for treatment individualization in this disease.

Mercaptopurine/Methotrexate maintenance therapy of childhood acute lymphoblastic leukemia: clinical facts and fiction

The antileukemic mechanisms of 6-mercaptopurine (6MP) and methotrexate (MTX) maintenance therapy are poorly understood, but the benefits of several years of myelosuppressive maintenance therapy for acute lymphoblastic leukemia are well proven. Currently, there is no international consensus on drug dosing. Because of significant interindividual and intraindividual variations in drug disposition and pharmacodynamics, vigorous dose adjustments are needed to obtain a target degree of myelosuppression. As the normal white blood cell counts vary by patients' ages and ethnicity, and also within age groups, identical white blood cell levels for 2 patients may not reflect the same treatment intensity. Measurements of intracellular levels of cytotoxic metabolites of 6MP and MTX can identify nonadherent patients, but therapeutic target levels remains to be established. A rise in serum aminotransferase levels during maintenance therapy is common and often related to high levels of methylated 6MP metabolites. However, except for episodes of hypoglycemia, serious liver dysfunction is rare, the risk of permanent liver damage is low, and aminotransferase levels usually normalize within a few weeks after discontinuation of therapy. 6MP and MTX dose increments should lead to either leukopenia or a rise in aminotransferases, and if neither is experienced, poor treatment adherence should be considered. The many genetic polymorphisms that determine 6MP and MTX disposition, efficacy, and toxicity have precluded implementation of pharmacogenomics into treatment, the sole exception being dramatic 6MP dose reductions in patients who are homozygous deficient for thiopurine methyltransferase, the enzyme that methylates 6MP and several of its metabolites. In conclusion, maintenance therapy is as important as the more intensive and toxic earlier treatment phases, and often more challenging. Ongoing research address the applicability of drug metabolite measurements for dose adjustments, extensive host genome profiling to understand diversity in treatment efficacy and toxicity, and alternative thiopurine dosing regimens to improve therapy for the individual patient.

Addressing genetic tumor heterogeneity through computationally predictive combination therapy

Recent tumor sequencing data suggest an urgent need to develop a methodology to directly address intratumoral heterogeneity in the design of anticancer treatment regimens. We use RNA interference to model heterogeneous tumors, and demonstrate successful validation of computational predictions for how optimized drug combinations can yield superior effects on these tumors both in vitro and in vivo. Importantly, we discover here that for many such tumors knowledge of the predominant subpopulation is insufficient for determining the best drug combination. Surprisingly, in some cases, the optimal drug combination does not include drugs that would treat any particular subpopulation most effectively, challenging straightforward intuition. We confirm examples of such a case with survival studies in a murine preclinical lymphoma model. Altogether, our approach provides new insights about design principles for combination therapy in the context of intratumoral diversity, data that should inform the development of drug regimens superior for complex tumors.

SIGNIFICANCE

This study provides the first example of how combination drug regimens, using existing chemotherapies, can be rationally designed to maximize tumor cell death, while minimizing the outgrowth of clonal subpopulations.

Is it time for a new paradigm for systemic cancer treatment? Lessons from a century of cancer chemotherapy

U.S. SEER (Surveillance Epidemiology and End Results) data for age-adjusted mortality rates for all cancers combined for all races show only a modest overall 13% decline over the past 35 years. Moreover, the greatest contributor to cancer mortality is treatment-resistant metastatic disease. The accepted therapeutic paradigm for the past half-century for the treatment of advanced cancers has involved the use of systemic chemotherapy drugs cytotoxic for cycling cells (both normal and malignant) during DNA synthesis and/or mitosis. The failure of this therapeutic modality to achieve high-level, consistent rates of disease-free survival for some of the most common cancers, including tumors of the lung, colon breast, brain, melanoma, and others is the focus of this paper. A retrospective assessment of critical milestones in cancer chemotherapy indicates that most successful therapeutic regimens use cytotoxic cell cycle inhibitors in combined, maximum tolerated, dose-dense acute treatment regimens originally developed to treat acute lymphoblastic leukemia and some lymphomas. Early clinical successes in this area led to their wholesale application to the treatment of solid tumor malignancies that, unfortunately, has not produced consistent, long-term high cure rates for many common cancers. Important differences in therapeutic sensitivity of leukemias/lymphomas versus solid tumors can be explained by key biological differences that define the treatment-resistant solid tumor phenotype. A review of these clinical outcome data in the context of recent developments in our understanding of drug resistance mechanisms characteristic of solid tumors suggests the need for a new paradigm for the treatment of chemotherapy-resistant cancers. In contrast to reductionist approaches, the systemic approach targets both microenvironmental and systemic factors that drive and sustain tumor progression. These systemic factors include dysregulated inflammatory and oxidation pathways shown to be directly implicated in the development and maintenance of the cancer phenotype. The paradigm stresses the importance of a combined preventive/therapeutic approach involving adjuvant chemotherapies that incorporate anti-inflammatory and anti-oxidant therapeutics.

Challenges and opportunities in childhood cancer drug development

Advances made in the treatment of childhood malignancies over the past four decades have resulted in overall 5-year survival rates of approximately 80%. However, despite these advances, several childhood cancers still have unacceptably low cure rates, and, even when treatment is successful, the acute and long-term morbidity of current therapy can be substantial. The development of molecularly targeted anticancer drugs offers the prospect of more effective therapy with fewer side effects, but will require increasing partnership between governments, and the academic and private sectors.

No advantage of a rotational continuation phase in acute lymphoblastic leukemia in childhood treated with a BFM back-bone therapy

BACKGROUND

Our aim was to compare two different schedules of maintenance in pediatric acute lymphoblastic leukemia (ALL) treated with a BFM-based therapy, in a randomized study: an Arm with 6-MP + MTX (with or without vincristine and dexamethasone pulses) versus a more intensive continuation phase.

PROCEDURE

From January 1996 to November 2002, 429 eligible children with ALL were enrolled in a protocol with BFM-based back-bone, followed by a randomized continuation phase in standard (SRG) and intermediate (IRG) risk groups. Patients were randomized between Arms A and B for SRG and B or C for IRG. Arms A and C consisted of 6-MP and MTX and in Arm C, six pulses of VCR and dexamethasone were added. Arm B combined four pairs of drugs rotated weekly. All risk-groups received maintenance until completing 2 years of therapy from diagnosis.

RESULTS

With a median follow-up of 138 (range: 96-178) months, the overall pEFS (SE) was 72 (6)% for all patients and the different risk groups showed: SRG: 85 (3)%, IRG: 71 (1)%, and HRG: 42 (7)% (P-value ≤ 0.0001). The pDFS (SE) according to the assigned arm of maintenance was, for Arm A: 89 (3)% and for Arm B: 85 (4)% in SRG, and, for Arm B: 77 (4)% and for Arm C: 75 (4)% in IRG, at 10 years follow-up. There were no statistically significant differences in outcome between arms of maintenance for both risk groups.

CONCLUSIONS

In protocols with initial BFM-based strategy, a more intensive continuation phase did not benefit any risk group of patients.

Challenges in implementing individualized medicine illustrated by antimetabolite therapy of childhood acute lymphoblastic leukemia

Predicting the response to medical therapy and subsequently individualizing the treatment to increase efficacy or reduce toxicity has been a longstanding clinical goal. Not least within oncology, where many patients fail to be cured, and others are treated to or beyond the limit of acceptable toxicity, an individualized therapeutic approach is indicated. The mapping of the human genome and technological developments in DNA sequencing, gene expression profiling, and proteomics have raised the expectations for implementing genotype-phenotype data into the clinical decision process, but also multiplied the complex interaction of genetic and other laboratory parameters that can be used for therapy adjustments. Thus, with the advances in the laboratory techniques, post laboratory issues have become major obstacles for treatment individualization. Many of these challenges have been illustrated by studies involving childhood acute lymphoblastic leukemia (ALL), where each patient may receive up to 13 different anticancer agents over a period of 2-3 years. The challenges include i) addressing important, but low-frequency outcomes, ii) difficulties in interpreting the impact of single drug or single gene response data that often vary across treatment protocols, iii) combining disease and host genomics with outcome variations, and iv) physicians' reluctance in implementing potentially useful genotype and phenotype data into clinical practice, since unjustified downward or upward dose adjustments could increase the of risk of relapse or life-threatening complications. In this review we use childhood ALL therapy as a model and discuss these issues, and how they may be addressed.

Phase I oncology studies: evidence that in the era of targeted therapies patients on lower doses do not fare worse

PURPOSE

To safely assess new drugs, cancer patients in initial cohorts of phase I oncology studies receive low drug doses. Doses are successively increased until the maximum tolerated dose (MTD) is determined. Because traditional chemotherapy is often more effective near the MTD, ethical concerns have been raised about administration of low drug doses to phase I patients. However, a substantial portion of oncology trials now investigate targeted agents, which may have different dose-response relationships than cytotoxic chemotherapies.

EXPERIMENTAL DESIGN

Twenty-four consecutive trials treating 683 patients between October 1, 2004, and June 30, 2008, at MD Anderson Cancer Center were analyzed. Patients were assigned to a low-dose (<or=25% MTD), medium-dose (25-75% MTD), or high-dose (>or=75% MTD) group, and groups were compared for response rate, time-to-treatment failure, progression-free survival, overall survival, and toxicity. To remove negatively biasing data from the high-dose group, in a second analysis, patients treated above the MTD were excluded (high-dose group, 75-100% MTD). Of the 683 patients, 97.7% received targeted agents.

RESULTS

Even when excluding patients above the MTD, there was an early trend favoring the low- versus high-dose group in time-to-treatment failure, with 32.9% versus 25.2% of patients on therapy at 3 months (P = 0.08). In addition, the low-dose group fared at least as well as the other groups in all other outcomes, including response rate, progression-free survival, overall survival, and toxicity.

CONCLUSIONS

These data may help alleviate concerns that patients who receive low drug doses on contemporary phase I oncology trials fare worse and suggest targeted agents may have different dose-response relationships than cytotoxic chemotherapies.

Vincristine: Can its therapeutic index be enhanced?

Vincristine is one of the most widely used and more effective drugs in paediatric oncology. The dose-limiting toxicity of neuropathy, lack of proven neuroprotective measures and an incomplete understanding of the pharmacokinetics and pharmacogenetics of vincristine have limited its therapeutic potential. Recent advances in the understanding of vincristine pharmacokinetics and pharmacogenetics, and potential methods of preventing neurotoxicity are reviewed which could enable dose escalation and dose individualisation in order to enhance the therapeutic index.

A history of cancer chemotherapy

The use of chemotherapy to treat cancer began at the start of the 20th century with attempts to narrow the universe of chemicals that might affect the disease by developing methods to screen chemicals using transplantable tumors in rodents. It was, however, four World War II-related programs, and the effects of drugs that evolved from them, that provided the impetus to establish in 1955 the national drug development effort known as the Cancer Chemotherapy National Service Center. The ability of combination chemotherapy to cure acute childhood leukemia and advanced Hodgkin's disease in the 1960s and early 1970s overcame the prevailing pessimism about the ability of drugs to cure advanced cancers, facilitated the study of adjuvant chemotherapy, and helped foster the national cancer program. Today, chemotherapy has changed as important molecular abnormalities are being used to screen for potential new drugs as well as for targeted treatments.

Mechanisms of antifolate resistance and methotrexate efficacy in leukemia cells

Antifolates are the first class of antimetabolites introduced to clinic about 6 decades ago. Now, after several years of administration of antifolates against malignancies and particularly leukemia, we are still trying to achieve a full understanding of the mechanisms of action and resistance to these agents. The present article covers different factors able to influence efficacy of antifolates on leukemic cells, the known mechanisms of resistance to methotrexate (MTX) and strategies to overcome these mechanisms. The dominant factors that are contributed to tolerance to cytocidal effects of MTX including pharmacokinetic factors, impaired transmembrane uptake as the most frequent rote of provoking resistance to MTX, augmented drug efflux, impaired intracellular polyglutamation as a determining process of drug efficacy, alterations in expression or activity of target enzymes and increased intracellular folate pools; and finally role of 7-hydroxymethotrexate on response or resistance to MTX will be discussed in more detail. Finally, strategies to overcome resistance to antifolates are discussed.

Pulses of vincristine and dexamethasone in addition to intensive chemotherapy for children with intermediate-risk acute lymphoblastic leukaemia: a multicentre randomised trial

BACKGROUND

Studies in the 1970s and 1980s suggested that the outcome of childhood acute lymphoblastic leukaemia (ALL) could be improved by intensification of conventional continuation chemotherapy with pulses of vincristine sulfate and steroids. We aimed to investigate the efficacy and toxic effects of vincristine-dexamethasone pulses as an addition to the continuation-therapy phase in a large cohort of children with intermediate-risk disease who were treated with the Berlin-Frankfurt-Münster (BFM) treatment strategy.

METHODS

3109 children, diagnosed with ALL and intermediate-risk features, were enrolled by eight participating organisations in eleven countries. All were treated with very similar protocols based on the BFM treatment strategy, which included induction, consolidation, reinduction, and continuation-therapy phases. At the beginning of the continuation-therapy phase, those patients in complete remission were randomly assigned to either a treatment or a control group. Control patients were given conventional mercaptopurine and methotrexate chemotherapy only. Patients in the treatment arm were also given pulses of vincristine (1.5 mg/m2 weekly for 2 weeks) and dexamethasone (6 mg/m2 daily for 7 days) every 10 weeks for six cycles. The primary outcome measure was disease-free survival. Analysis was by intention to treat. The study is registered at http://www.clinicaltrials.gov with the identifier NCT00411541.

FINDINGS

174 patients (5.6%) relapsed or died in complete remission before randomisation. Of the remaining 2935 patients, 2618 (89.2%) were randomly assigned: 1325 to the treatment group and 1293 to the control group. With median follow-up of 4.8 years, 240 children in the treatment group and 241 in the control group had relapses; 15 in the treatment group and 14 controls died in complete remission or developed second malignant neoplasms. The 5-year and 7-year disease-free survival estimates were 79.8% (SE 1.2) and 77.5% (1.5) in the treatment group and 79.2% (1.2) and 78.4% (1.3) in the control group, respectively. Treatment with pulses of vincristine and dexamethasone was associated with a non-significant 3% relative-risk reduction (hazard ratio 0.97; 95% CI 0.81-1.15; p=0.70).

INTERPRETATION

Children with intermediate-risk ALL who received intensive chemotherapy based on BFM protocols did not benefit from intensification of the continuation-therapy phase with a schedule of pulses of vincristine and dexamethasone.

Vincristine pharmacokinetics and response to vincristine monotherapy in an up-front window study of the Dutch Childhood Leukaemia Study Group (DCLSG)

The relationship between vincristine pharmacokinetics and its antileukaemic effect in children is unknown. Since vincristine plays a key role in the treatment of childhood acute lymphoblastic leukaemia (ALL), it is worthwhile to explore if efficacy can be improved by individual dose adjustment. Therefore, we studied the relationship between vincristine antileukaemic effect and pharmacokinetics in children newly diagnosed with ALL before the start of standard induction chemotherapy. Vincristine plasma concentration was measured by high-pressure liquid chromatography analysis with electrochemical detection. Primary pharmacokinetic parameters were estimated by maximum a posteriori parameter estimation with a Bayesian algorithm using the ADAPT II software package. Secondary pharmacokinetic parameters were calculated from the model. Response to a single dose of vincristine was determined on bone marrow (BM) and peripheral blood (PB) smears after 3 days. Variability of vincristine pharmacokinetics did not explain variability of response to vincristine monotherapy. Our results do not support the clinical application of pharmacokinetically guided adaptation of a standard body surface area-based dose of vincristine.

Increasing the dosage of vincristine

BACKGROUND

Vincristine (VCR) is widely used to treat patients with malignant disease; among the patients treated with VCR are children with brain tumors. In vitro studies have demonstrated that the cytotoxic activity of VCR is related to both extracellular concentration and duration of exposure. The attainment of higher plasma concentrations by injecting larger bolus doses of VCR has been limited by concerns about neurotoxicity. One possible alternative strategy for enhancing the antitumor efficacy of VCR involves prolonging the duration of in vivo exposure. Therefore, the authors explored the neurotoxicity and pharmacokinetics of VCR administered via a 96-hour continuous infusion after administration of a conventional bolus dose in a pediatric population.

METHODS

The current study included 16 patients, 11 of whom were males. The median age of the study population was 4.8 years (range, 1.7-15.8 years). The diagnoses included intrinsic pontine glioma (n = 4), ependymoma (n = 5), astrocytoma (n = 3), medulloblastoma/primitive neuroectodermal tumor (PNET; n = 2), ganglioglioma (n = 1), and choroid plexus carcinoma (n = 1). Of the 16 patients, 5 were newly diagnosed, and the remaining 11 had disease recurrences, 8 of which arose after radiotherapy. Treatment included cyclophosphamide 65 mg/kg administered intravenously over 1 hour on Day 1, a bolus of VCR 1.5 mg/m(2) administered intravenously on Day 2, and VCR 0.5 mg/m(2) per 24 hours administered via continuous intravenous infusion on Days 2-5. Thus, a total VCR dose of 3.5 mg/m(2) was administered via infusion over 4 days. Fifteen patients received 2 courses of treatment at 21-28-day intervals, and a total of 31 treatment courses were administered. VCR concentrations in plasma samples were measured using high-performance liquid chromatography.

RESULTS

Jaw pain, constipation, mild abdominal pain, and depressed reflexes were common. However, only 1 of 31 courses was associated with Grade III toxicity, and no Grade IV toxicity (e.g., cranial nerve palsy, ileus, inappropriate antidiuretic hormone secretion, seizures, hallucinations, etc.) was noted. The steady-state plasma concentration of VCR during continuous infusion ranged from 1 to 3 microg/L in all patients. Responses after 2 courses were evaluated in 14 of 16 patients. A complete response was noted in one patient (astrocytoma), a partial response in three patients (one each with astrocytoma, ependymoma, and PNET), stable disease in seven patients, and disease progression in three patients.

CONCLUSIONS

Continuous infusion of VCR after a conventional bolus dose plus cyclophosphamide for children with tumors of the central nervous system did not result in significant neurotoxicity and appeared to be a safe strategy for achieving increased systemic exposure.

A descriptive study of randomized trials of treatments for childhood acute lymphoblastic leukaemia

This report presents a historical and descriptive account of randomized trials in childhood leukaemia since the earliest such studies in the 1960s. It focuses on trials that began before 1988, making use of the register of trials developed for a systematic review of treatments for acute lymphoblastic leukaemia in children. The number of randomized trials starting each year increased from one or two in the 1960s to an annual average of five or six in the 1980s. However trials remained relatively small, with more than half of all randomizations accruing less than 200 patients and only five having more than 1000. Most trials were published more than once.

Pharmacokinetics of vincristine monotherapy in childhood acute lymphoblastic leukemia

We studied vincristine pharmacokinetics in 70 children newly diagnosed with acute lymphoblastic leukemia, after a single dose of vincristine as monotherapy. Vincristine plasma concentrations were measured by HPLC analysis. A two-compartment, first-order pharmacokinetic model was fitted to the data by maximum a posteriori parameter estimation. In this group of children pharmacokinetic factors were highly variable: median (25th and 75th percentiles) total body clearance, 228 (128-360) mL.min(-1).m(-2); elimination half-life, 1001 (737-1325) min; apparent volume of distribution at steady state 262 (158-469) L/m(2). Vincristine clearance was substantially slower than has been reported previously for children receiving vincristine in combination with steroids as part of combination chemotherapy (median clearance, 228 mL.min(-1).m(-2) versus mean clearance, 381 and 482 mL. min(-1). m(-2), respectively). Steroids are known as inducers of vincristine-metabolizing cytochrome P(450) 3A4 enzymes. The absence of steroids during our study appears to be the most likely explanation for this difference. Furthermore, we found that vincristine clearance was faster in patients with hyperdiploid (>50 chromosomes) than in patients with diploid or hyperdiploid (46-50 chromosomes) leukemic blasts.

Continuing therapy for childhood acute lymphoblastic leukaemia: clinical and cellular pharmacology of methotrexate, 6-mercaptopurine and 6-thioguanine

Across the world, therapy with 6-mercaptopurine (6-MP) and methotrexate (MTX) forms the basis of the continuing therapy of childhood acute lymphoblastic leukaemia (ALL). In this review, the pharmacological determinants of the sensitivity of human leukaemia cell lines and lymphoblasts derived from children with ALL will be discussed. In addition, clinical pharmacological studies of 6-MP and MTX in relation to the continuing therapy with childhood ALL will be reviewed. For 6-MP in vitro, prolonged exposure times to relatively high extracellular drug concentrations are necessary for cytotoxicity, and these concentrations are much higher than those achieved during continuing therapy for childhood ALL. For MTX, plasma concentrations are achieved during continuing therapy that would be cytotoxic to human leukaemia cells during prolonged exposures in vitro. For both MTX and 6-MP, wide inter- and intrapatient variation in plasma pharmacokinetic parameters has been described. For 6-MP and MTX, cellular pharmacological studies have been largely restricted to erythrocytes as a surrogate of the possible effects in leukaemic blasts. Although measures of the pharmacology of 6-MP and MTX in erythrocytes has been related to prognosis in many studies, 6-MP systemic exposure and the dose intensity of 6-MP and MTX actually received by children during this phase of therapy seems to be the most important determinant of efficacy. Further studies will be needed to determine the importance of pharmacokinetic variability during continuing therapy as a determinant of outcome for children with ALL. In this respect, minimal residual disease status during this phase of treatment may prove to be a useful pharmacodynamic endpoint.

Haemopoietic growth factors in paediatric oncology: a review of the literature

Recombinant haemopoietic growth factors (HGFs) are an attractive adjunct to reduce morbidity from chemotherapy regimens and their use has become widespread in paediatric oncology. Although patients receiving HGFs often have faster haematological recovery after intensive chemotherapy, this does not always translate into meaningful clinical benefits. This article reviews the clinical effectiveness of HGFs in a variety of different contexts. Most published studies have used granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF) as prophylaxis to ameliorate the subsequent neutropenia following intensive chemotherapy. These 2 agents have also been used to mobilise peripheral blood stem cells for autologous transplantation. HGFs specific for anaemia and thrombocytopenia are currently in paediatric clinical trials and it is hoped that the proper context and administration strategy can be found to make their use clinically effective. This article also reviews data on toxicity, specifically focusing on differences between various formulations of growth factors. HGFs are expensive, and cost-benefit analyses reviewed in this article give an important perspective on the financial aspects of paediatric cancer care. Because HGFs do not benefit every child receiving chemotherapy and overuse increases costs and may result in unnecessary adverse effects, evidence-based guidelines for their rational use in paediatric oncology are proposed.

Therapy for acute myeloid leukemia: intensive timing of induction chemotherapy

Children's Cancer Group (CCG) study 2891 for children with previously untreated acute myeloid leukemia enrolled more than 1200 patients between 1989 and 1995. This study showed that increased dose intensity during induction therapy improved survival for all patients except those with Down syndrome, where it proved harmful. Although increased dose intensity improved survival, it did not improve remission induction rate, indicating that the quality of remissions varies. This finding complicates the evaluation of postremission therapy options, which CCG 2891 also evaluated. Survival with related-donor allogeneic bone marrow transplantation was superior to survival with both purged autologous bone marrow transplantation and a more standard chemotherapy consolidation, whereas survival for autologous transplantation and chemotherapy was equivalent.

Prediction of methotrexate elimination after high dose infusion in children with acute lymphoblastic leukaemia using a population pharmacokinetic approach

High-dose methotrexate (HD-MTX) with leucovorin rescue is a component of therapy in children with acute lymphoblastic leukaemia. Since MTX toxicity is related to drug exposure, a monitoring of serum MTX concentrations at H24, H48, H72 and until the concentration is less than 0.2 micromol/L is commonly performed. However, a number of patients may reach concentrations of less than 0.2 micromol/L long before the next sampling is scheduled. The aim of our study was to develop a Bayesian method predicting the time at which MTX concentration reaches 0.2 micromol/L in order to decrease the number of samples drawn and to allow for a more rapid patient discharge. Methotrexate population parameters were estimated from a retrospective analysis of 60 infusions in 23 children and MTX concentrations were predicted from an independent set of 20 courses in 14 children with a Bayesian approach using either one (H48) or two (H24 and H48) samples. The following population parameters were obtained using a two-compartment model: CL = 3.51 L/h (inter-individual variability: 66%), Vd = 8.67 L (58%), k12 = 0.0044 h(-1)(105%), k21 = 0.039 h(-1)(25%). Clearance and Vd were found to increase with weight and age respectively. Both sampling schedules tested for the Bayesian estimation enabled accurate prediction of concentrations and provided satisfactory precision despite a small bias. When considering the ability to predict the time at which the threshold was reached, the one-sample (H48) schedule gave the best results. We conclude that a sampling schedule involving only one sample and Bayesian parameter estimation may be able to predict the delay necessary to reach 0.2 micromol/L in each individual.

Interferon treatment of chronic active hepatitis C during therapy of acute lymphoblastic leukemia

Due to concerns that antineoplastic therapy produces prolonged decrease in immune function, interferon treatment of chronic active hepatitis C (CAHC) has been used only at one year or longer after the end of cancer therapy. We report the experience of an 11-year-old who developed symptomatic CAHC at the start of maintenance therapy for testicular relapse of acute lymphoblastic leukemia (ALL). Significant dose reduction of maintenance therapy did not improve the tolerance of antileukemic treatment. In an effort to improve his liver disease and to deliver effective antileukemic therapy, interferon alpha and an alternative maintenance therapy regimen for ALL were initiated. The patient tolerated the combined therapy well. Interferon therapy was continued for 27 months, which was three months from the end of antineoplastic therapy. At that time serum transaminase values were normal, and no HCV viral genome was detectable. Viral genome was detected 10 months later. The combined effects of interferon and antineoplastic therapy resulted in myelosuppression requiring dose reduction of both treatments. The patient remains asymptomatic and with no evidence of recurrent leukemia more than six years from diagnosis of relapse. The effect on the status of this patient's CAHC was similar to that reported among leukemic patients who underwent an interferon course more than one year from the end of antineoplastic therapy. Interferon treatment of CAHC can be given concomitantly with antineoplastic therapy.

Dose-response effect of adjuvant cyclophosphamide, methotrexate, 5-fluorouracil (CMF) in node-positive breast cancer. International Breast Cancer Study Group

There is evidence in the literature of a relationship between dose and response to adjuvant chemotherapy for breast cancer, although published results are conflicting. We therefore retrospectively analysed the role of dose response in patients included in four adjuvant trials of the International Breast Cancer Study Group (IBCSG, formerly the Ludwig Breast Cancer Study Group (trials I, II, III and V), all using 'classical' cyclophosphamide, methotrexate, and 5-fluorouracil (CMF). A total of 1385 node-positive patients were treated with oral cyclophosphamide, and intravenous methotrexate plus 5-fluorouracil (CMF) for at least six 4 week courses. 1350 of these were included in 6 month landmark treatment outcome analyses. A total of 1029 patients were premenopausal, 321 were postmenopausal; 800 had one to three and 550 more than three involved axillary nodes at surgery. The median follow-up ranged from 12 years for trial V to 15 years for trials I-III. Patients were grouped according to three prospectively defined dose levels based on the percentage of the protocol prescribed dose that was actually administered (level I > or = 85%, level II 65-84%, level III < 65%). Patients who received dose level II had a higher disease-free (P = 0.07) and overall survival (P = 0.03) than those who received a higher (level I) or lower (level III) percentage. The 10 year overall survival was 60% for dose level II, 56% for dose level I, 51% for dose level III. The results were generally consistent within trial, menopausal status, and oestrogen receptor status groups. The results within nodal groups showed a large difference among the dose levels for the group with one to three positive nodes (P = 0.02), but no difference for the group with four or more positive nodes. Our results indicate that the dose-response effect remains a crucial factor in adjuvant chemotherapy of breast cancer. Reductions larger than 35% in the dose administered of oral CMF adversely influenced the outcome of breast cancer patients and should be avoided. The better outcome of the intermediate dose group indicates the need to investigate other aspects involved in the cytotoxicity of adjuvant CMF chemotherapy.

Conventional compared with individualized chemotherapy for childhood acute lymphoblastic leukemia

BACKGROUND

The rate of clearance of antileukemic agents differs by a factor of 3 to 10 among children with acute lymphoblastic leukemia. We hypothesized that the outcome of treatment would be improved if doses were individualized to prevent low systemic exposure to the drugs in patients with fast drug clearance.

METHODS

We stratified and randomly assigned 182 children with newly diagnosed acute lymphoblastic leukemia to postremission regimens that included high-dose methotrexate and teniposide plus cytarabine. The doses of these drugs were based on body-surface area (in the conventional-therapy group) or the rates of clearance of the three medications in each patient (in the individualized-treatment group). In the individualized-treatment group, doses were increased in patients with rapid clearance and decreased in patients with very slow clearance.

RESULTS

Patients who received individualized doses had significantly fewer courses of treatment with systemic exposures below the target range than did patients who received conventional doses (P<0.001 for each medication). Among the patients with B-lineage leukemia, those who received individualized therapy had a significantly better outcome than those given conventional therapy (P=0.02); the mean (+/-SE) rates of continuous complete remission at five years were 76+/-6 percent and 66+/-7 percent, respectively. There was no significant difference between treatments for patients with T-lineage leukemia (P=0.54). In a proportional-hazards model, the time-dependent systemic exposure to methotrexate, but not to teniposide or cytarabine, was significantly related to the risk of early relapse in children with B-lineage leukemia.

CONCLUSIONS

Adjusting the dose of methotrexate to account for the patient's ability to clear the drug can improve the outcome in children with B-lineage acute lymphoblastic leukemia.

Regional perfusion with hemofiltration (chemofiltration) for the treatment of patients with regionally advanced cancer

BACKGROUND

Regionally advanced cancer is a common, often unresolved problem. Effective local control with chemotherapy is limited by the toxicity following systemic administration. Chemofiltration (CF) is a form of regional perfusion that enables the administration of cytotoxic drugs into one body area while limiting systemic toxicity. The drug is infused into the artery supplying the involved area. The venous effluent of the same organ is pumped out into a hemofiltration unit at a high flow rate. The drug is then filtered away and the blood returned to systemic circulation.

METHODS

Forty-one patients underwent 45 CF. Twenty-four patients had CF of the pelvis for advanced rectal carcinoma (10), malignant melanoma (6), and cancers of the uterine cervix (3), ovary (2), vulva (1), endometrium (1), and anus (1). Seventeen patients underwent CF of the liver for metastatic colon (10), breast (4), pancreas (1), ovary (1), and unknown primary (1) cancer. 5-fluorouracil (1 g/m2) and mitomycin-C (30 mg/m2); cisplatinum (200 mg/m2) alone or combined with bleomycin (50 mg/m2) and mitomycin-C (20 mg/m2); or melphalan (1 mg/kg) were the combinations used.

RESULTS

Generally the procedure was well tolerated. Complications included transient leukopenia (18), paralytic ileus (2), hair loss (2), renal failure (1). Two patients died within 40 days following CF. Of 36 evaluable patients, 16 (44%) had partial response, 14 (38%) had stable disease, and 6 (18%) had disease progression. A decrease of at least 30% in carcinoembryonic antigen levels occurred in 12 of 24 patients (50%). Median time to progression was 7 months. Ten of 13 patients (77%) achieved good symptomatic palliation.

CONCLUSIONS

The results of CF in our study are not superior to alternative methods of drug delivery to the liver and pelvis. However, considering that previous systemic chemotherapy had failed two-thirds of the patients, some benefit may be attributed to this regional delivery modality. Furthermore, pelvic CF afforded very significant symptomatic relief which was definitely superior to other methods.

Duration and intensity of maintenance chemotherapy in acute lymphoblastic leukaemia: overview of 42 trials involving 12 000 randomised children

BACKGROUND

The effects on long-term outcome in childhood acute lymphoblastic leukaemia (ALL) of the duration and the intensity of maintenance chemotherapy need to be assessed reliably. With this objective the Childhood ALL Collaborative Group coordinated a worldwide overview of all randomised trials that began before 1987.

METHODS

Individual patient data were sought for about 3900 children in trials of longer vs shorter maintenance (eg, 3 vs 2 years), 3700 in trials of intensive "reinduction" chemotherapy during maintenance, and 4400 in trials of various other questions, including 1300 in trials of pulses of vincristine and prednisone (VP) during maintenance. Analyses were of survival in first remission, overall survival, and cause-specific mortality.

FINDINGS

Deaths during remission were increased by longer maintenance (2.7 percent vs 1.2 percent), VP pulses (4.0 vs 3.2 percent), and intensive reinduction (4.8 percent vs 3.3 percent), but these increases were counterbalanced by reductions in relapses. Total events (relapse or death) were significantly reduced by longer maintenance (23.3 percent vs 27.6 percent), VP pulses (31.2 percent vs 40.4 percent) and intensive reinduction (27.8 percent vs 35.8 percent) (each 2p<0.001). Many of those who relapsed were successfully re-treated, however, and only for intensive reinduction was overall survival significantly improved (18.5 percent vs 22.3 percent; 2p=0.01).

INTERPRETATION

Intensive reinduction chemotherapy in these trials produced an absolute improvement of about 4 percent in long-term survival; if the extra deaths in remission had been avoided, this would have been a 5 percent benefit. Further improvements in survival seem more likely to be obtained with intensive treatment than with longer low-level maintenance.

Non-cryopreserved, limited number (1 or 2) peripheral blood progenitor cell (PBPC) collections following GCSF administration provide adequate hematologic support for high dose chemotherapy

Sixty-two patients with a variety of malignant diseases including 44 with breast cancer, seven with sarcomas, five with germ cell tumours, four with Hodgkin's disease and two with multiple myeloma received short duration, high dose chemotherapy, with non-cryporeserved peripheral blood progenitor cell rescue as treatment for malignancy. Limited, (one or two) peripheral blood precursor cell collections were performed following either cyclophosphamide, cyclophosphamide+GCSF or GCSF priming. Total nucleated cell and CD34+ cell yields were significantly higher with either of the two GCSF priming regimens as compared to cyclophosphamide only priming. Cell viability at the time or reinfusion was also enhanced by GCSF priming. Chemotherapy regimens included either high dose cyclophosphamide, mitoxantrone and VP16 (HD-CNV); high dose melphelan plus VP16; high dose BCNU, cyclophosphamide and VP16 (BCV); or high carboplatin, cyclophosphamide and VP16 (PCV) all given over 8-12 h. Non-cryopreserved blood progenitor cells, stored at 4 degrees C, were reinfused 24 h after completion of chemotherapy. Sixty-one of 62 patients showed hematologic recovery. Median time to hematologic recovery was significantly shorter for patients receiving GCSF primed cell collections. There was also significantly less hospitalization and antibiotic usage for patients receiving GCSF primed precursor cell collections. The addition of post chemotherapy GCSF did not, however, appear to enhance the rate of hematologic recovery. This study shows that simplified schedules for high dose chemotherapy administration together with simple precursor cell collection procedures provide safe and effective methods for administering myeloablative chemotherapy treatment.

Hyperthermic isolated limb perfusion with cis-diamminedichloro-platinum. II. An experimental study in dogs with a balloon-occlusion technique for repeated high-dose treatment

Isolated organ perfusion is attractive for regional high-dose chemotherapy because of its advantage to reduce whole body toxicity. Intraoperative hyperthermic isolated perfusion procedures involving a heart-lung machine have been developed, but repeated treatments carry a high risk of vessel and tissue damage. Therefore, a study of isolated hyperthermic limb perfusion in four dogs was conducted using a balloon-occlusion technique including a hyperthermia unit, two low-flow rotary pumps, a bubble oxygenator, and two polyurethane balloon catheters. After 15 min infusion of cisplatinum the concentrations of serum platinum (Pt) in the isolated limb and in the whole body were measured by atomic absorption spectroscopy. Regional exposure to Pt was more than 10-fold higher than systemic exposure. After 60 min isolated limb perfusion, the area under the curve (AUC) of Pt concentrations in the isolated limb showed values between 767.4 and 1055.6 micrograms/l x 60 min, whereas in the whole body values between 59.8 and 75.9 micrograms/l x 60 min were obtained. Repeated isolated limb perfusions with the balloon-occlusion technique were performed in three dogs without systemic side effects. This model of regional chemotherapy may be useful for preoperative chemotherapy in malignant tumors of the limbs.

Treatment of acute lymphoblastic leukemia. 30 years' experience at St. Jude Children's Research Hospital

BACKGROUND

Therapy for childhood lymphoblastic leukemia has evolved during the past three decades, but key questions about what are the least toxic, most effective forms of treatment remain unanswered because of the lack of comprehensive follow-up information.

METHODS

To assess long-term outcome in the series of clinical trials conducted at St. Jude Hospital, we compared the results of treatment typical of four eras: exploratory combination chemotherapy (era 1, 1962 to 1966; 91 patients), regimens for the control of meningeal leukemia (era 2, 1967 to 1979; 825 patients), limited intensification of therapy (era 3, 1979 to 1983; 428 patients), and extended intensification of therapy (era 4, 1984 to 1988; 358 patients). ("Intensification" refers to strategies of systemic chemotherapy that are more aggressive than conventional ones.) The major end points were survival and event-free survival; we also calculated the relative risk of treatment failure and the rate of relapse or death after treatment ended (post-treatment failure rate).

RESULTS

The probability of event-free survival improved significantly in each successive era (P < 0.001 by the log-rank test), reaching 71 percent in era 4. There was a decrease of approximately 50 percent in the risk of treatment failure from one era to the next in each subgroup of patients defined according to different combinations of the leukocyte count, race, age, and sex. Leukemia appeared to be eradicated in patients who remained in complete remission for three years or more after treatment in era 4. The incidence of death due to nonleukemic causes remained 4 to 6 percent despite the trend toward more intensive treatment. An estimated 765 patients (45 percent) are long-term survivors; most of them (80 percent) have no health problems related to leukemia or its treatment.

CONCLUSIONS

The development and successful application of preventive therapy for meningeal leukemia, followed by the intensification of systemic chemotherapy, has progressively improved the rate of cure of childhood lymphoblastic leukemia, with relatively few adverse sequelae.

Granulocyte colony-stimulating factor (G-CSF) as an adjunct to induction chemotherapy of adult acute lymphoblastic leukemia (ALL)

Our purpose was to evaluate the ability of recombinant human granulocyte colony-stimulating factor (r-metHuG-CSF) as an adjunct to induction chemotherapy of acute lymphoblastic leukemia (ALL) to ameliorate chemotherapy-induced neutropenia and thus allow patients to receive full doses of chemotherapy on time. Sixteen consecutive patients with adult ALL (13 de novo, three relapsed) were treated with induction chemotherapy according to the BMFT protocol and received in addition r-metHuG-CSF (200 micrograms/m2/day). Patients who were treated with the same induction chemotherapy but without G-CSF between 1982 and 1990 served as controls. Fifteen of the 16 patients achieved complete hematological remission. One patient died because of fungal septicemia. Compared with historical controls, G-CSF-treated patients had a significantly faster neutrophil recovery in phase I, resulting in neutrophil counts > 1000/microliters at day 17 vs day 26 (in median) in controls. In phase II, the onset of severe leukocytopenia (< 1500/microliters) was significantly (p = 0.01) delayed and the degree of leukocytopenia less pronounced (mean nadir 3300/microliters) in G-CSF-treated patients compared with controls (1880/microliters). The number of days of febrile neutropenia was not different in phase I. In phase II it was lower in study patients (0 vs 1.1 days), but the difference did not reach statistical significance (p = 0.09). Full doses of chemotherapy could be given on time to 11/13 (85%) G-CSF patients but to only 7/30 (23%) controls. These data indicate that (a) G-CSF can be given along with chemotherapy in induction treatment of ALL without compromising efficacy; (b) the duration of neutropenia in phase I is markedly shortened and the degree of leukocytopenia in phase II ameliorated; (c) these beneficial effects allow patients to receive full doses of chemotherapy on time.

Reduction of infection rates in cancer patients associated with the use of haematopoietic growth factors

As the risk of infection associated with chemotherapy is related to the depth of the fall in neutrophil counts, protection from neutropenia has been used as an endpoint for growth factors in this setting. However, the functional status of these and other myeloid cells are also important. Therefore, more direct measurements of clinical improvement will also be useful. Several studies have suggested that the use of granulocyte-macrophage colony-stimulating factor (GM-CSF) can result in improvements in hospital stay, days of fever, antibiotic use and thrombocytopenia. Similar findings have been confirmed by our own work which indicates that GM-CSF not only shortens the period of leukopenia, but also reduces the complications of infection. More sensitive and appropriate endpoints should be included in future trials, including rate of and survival from infection as well as overall and disease-free survival.

Lessons from 20 years of curative therapy of childhood acute leukaemia

The past 20 years of curative therapeutics of childhood acute leukaemia has been largely a period of consolidation of gains, refinement of techniques and dissemination of expertise and technology. However, certain lessons have been learned. First, cure can be permanent but the complexity and cost of curative treatment currently restricts its accessibility; prevention or simple curative treatment is needed. Secondly, cure of the child demands that the risk of adverse sequelae of treatments be carefully balanced with known therapeutic benefits. Thirdly, preventive meningeal irradiation is no longer required. Fourth, treatment intensification is self-limiting. Adverse reactions can cancel out or exceed therapeutic benefits, resulting in a lower cure rate or a similar cure rate with lower quality of cure. Finally, morphology, immunophenotype and genotype of acute leukaemia are important criteria for selecting and scheduling drug therapy. Genotype may be the most important since leukaemia is a genetic disorder for which morphology and immunophenotype are mere reflections. However, none of these features, individually or together, are sufficient to explain all the difference in outcome among children on a given treatment plan or to completely fulfill the need of criteria for selection of treatment. Acute leukaemia remains an unsolved problem demanding considerably more basic and clinical research to meet the need for prevention and simple dependable curative treatment.

Maintenance chemotherapy and cure of childhood acute lymphoblastic leukaemia

Maintenance chemotherapy with 6-mercaptopurine and methotrexate, widely believed an essential contribution to the high cure rates achieved in children with acute lymphoblastic leukaemia (ALL), is thought to work by killing the leukaemia cells that remain after intensive chemotherapy. We suggest instead that ALL commonly arises in precursor B cells normally programmed to die, and that maintenance chemotherapy does not kill these cells but controls growth of the leukaemia clone so that programmed death can occur. A similar approach may apply to other cancers in which programmed death is intrinsic to the normal counterparts of the neoplastic cells.

Prognostic significance of methotrexate and 6-mercaptopurine dosage during maintenance chemotherapy for childhood acute lymphoblastic leukemia

Tolerance of full-dose methotrexate/6-mercaptopurine (MTX/6MP) maintenance therapy for childhood acute lymphoblastic leukemia (ALL) without side effects could reflect insufficient systemic drug exposure, and drug withdrawals due to toxicity might reduce the chance of cure. The present study included 122 children with non-B cell acute lymphoblastic leukemia with a median follow-up of 84 months. Leukopenia and hepatotoxicity were calculated as weighted means of all white cell counts and all serum aminotransferase measurements, respectively, registered for each patient. Forty-five patients relapsed (30 in bone marrow). Patients tolerating an average dose of MTX of more than 75% of the recommended protocol doses and having cumulated drug withdrawals of less than 1% of the period of maintenance therapy had an increased risk of hematological relapse (p = 0.008) as well as of any relapse (p = 0.03) when compared to the remaining patients. Patients with a cumulative withdrawal of MTX or of 6MP for greater than 10% of the maintenance therapy period had an increased risk of hematological relapse (MTX: p = 0.009, 6MP: p less than 0.0001) and of any relapse (MTX: p = 0.16, 6MP: p = 0.0002). Liver toxicity was the main reason for cumulative long-term drug withdrawals. However, patients with a mean aminotransferase level above the upper normal limit (40 IU/l) who were kept on therapy (cumulative withdrawals of neither drug for more than 5% of their maintenance therapy period) had a significantly lower risk of hematological relapse (p = 0.02) as well as of any relapse (p = 0.06) than the remaining children. The concept of treating to toxicity seems warranted for maintenance therapy of childhood lymphoblastic leukemia.