An institutional review of genomic sequencing in pediatric solid tumors.

BACKGROUND: Although tumor genomic profiling has aided the advancement of targeted genetic therapy, its clinical integration remains a challenge in pediatric cancers due to lower mutation frequency and less available targeted drugs. There have been multiple novel studies examining molecular sequencing in pediatrics; however, many of these studies primarily utilized large-scale, genome-wide screening applications that limit applicable use due to the availability of testing. This study examined the institutional use of a targeted, clinically available approach to tumor genomic sequencing. METHODS: A retrospective chart review was performed on pediatric patients with solid tumors who were managed at Roswell Park Comprehensive Cancer Center and underwent molecular testing of their tumor biopsy via OmniSeq from August 2016 to July 2021. Results were reviewed for mutations considered to be "actionable" by targeted therapy. Patients with actionable mutations were further examined to evaluate treatment course, receival of targeted therapy, and clinical outcomes. RESULTS: We identified 64 pediatric patients consisting of 20 (31%) with CNS tumors and 44 (69%) with non-CNS tumors, ranging in age from 9 months to 21 years. Thirty-five total actionable mutations were identified amongst 27 patients (42%). Of these 27, 12 patients (44%) received at least 1 targeted drug against a respective actionable mutation, of which 6 patients (50%) achieved clinical benefit to therapy, including 1 complete response. CONCLUSIONS: The use of a clinically focused and readily available targeted molecular sequencing panel identified actionable mutations at a comparable rate to the large-scale, less readily available sequencing panels utilized in other studies. Half of our patients who received targeted therapy achieved a complete response or clinical benefit from therapy. Although targeted therapy has a role in pediatric cancer treatment, many newer drugs require further research on their safety and efficacy.

Multi-institution analysis of tumor mutational burden and outcomes in pediatric central nervous system tumor patients.

BACKGROUND: Pediatric central nervous system (CNS) tumors are the leading cause of pediatric cancer mortality. Research addressing genomic biomarkers and clinical outcomes is needed to inform therapeutic decision-making. METHODS: We conducted a retrospective analysis of pediatric patients (age <21) diagnosed with a primary CNS tumor at four upstate New York hospitals from 2008 to 2021. Clinical and histopathologic data were identified from each patient, including genomic analysis of somatic mutations and tumor mutational burden (TMB) where available. These variables were each compared with overall survival using Cox regression analyses. Multivariable analysis was conducted to identify patient characteristics that may independently predict survival. RESULTS: We identified 119 patients. Common tumor types included low-grade glioma (N = 51), high-grade glioma (N = 29), and medulloblastoma (N = 11). Common driver mutations included TP53 inactivation (N = 16), BRAF-KIAA1549 fusion (N = 16), FGFR1 amplification (N = 12), BRAF V600E mutation (N = 12), NF1 loss (N = 12), and H3F3A K28M mutation (N = 6). Median TMB was one mutation/megabase (mut/Mb, range = 0-132). Overall survival was 79.9%. Variables associated with poorer survival on univariable analysis were higher TMB (p = .002, HR 4.97), high-grade tumors (p = .009, HR 84.3), and high-grade glioma histology (p = .021, HR 3.14). Multivariable analyses further identified TMB (p = .011, HR 4.46) and high-grade histology (p = .015, HR 5.28) as independently predictive of worse survival. Tumor progression was more common in high-TMB (N = 15, 44%) than in low-TMB tumors (N = 19, 35%). CONCLUSIONS: High TMB is correlated with higher rates of progression and death as compared to low-TMB tumors. These findings may help identify patients who may benefit from alternative treatments, such as immunotherapies.

Pediatric Aggressive Mature B-Cell Lymphomas, Version 3.2022, NCCN Clinical Practice Guidelines in Oncology.

NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for Pediatric Aggressive Mature B-Cell Lymphomas include recommendations for the diagnosis and management of pediatric patients with primary mediastinal large B-cell lymphoma (PMBL) and sporadic variants of Burkitt lymphoma and diffuse large B-cell lymphoma. PMBL is now considered as a distinct entity arising from mature thymic B-cells accounting for 2% of mature B-cell lymphomas in children and adolescents. This discussion section includes the recommendations outlined in the NCCN Guidelines for the diagnosis and management of pediatric patients with PMBL.

Successful Bone Marrow Transplantation With Intensive Post-transplant Intrathecal Chemotherapy for CNS Relapsed AML in 2 Infants.

BACKGROUND: Infant acute myeloid leukemia is a rare but aggressive form of leukemia. OBSERVATION: We report 2 children who presented with hyperleukocytosis, subsequently diagnosed with infant acute myeloid leukemia, and both developed isolated central nervous system relapse while on chemotherapy. Both infants underwent successful bone marrow transplantation with myeloablative conditioning (thiotepa, busulfan, and cyclophosphamide) without radiation, followed by 12 empiric post-transplant lumbar punctures with intrathecal cytarabine. Both patients tolerated these therapies well, and are without infections, chronic graft-versus-host disease, or any post-transplant sequelae. CONCLUSION: Nonradiation-based conditioning followed by empiric central nervous system-directed intrathecal chemotherapy may be considered for high-risk infants with leukemia.

Novel Therapies Potentially Available for Pediatric B-Cell Non-Hodgkin Lymphoma.

Burkitt lymphoma, diffuse large B-cell lymphoma (DLBCL), and primary mediastinal B-cell lymphoma are the most common aggressive pediatric mature B-cell non-Hodgkin lymphomas (B-NHLs). Despite excellent survival with current chemotherapy regimens, therapy for Burkitt lymphoma and DLBCL has a high incidence of short- and long-term toxicities. Patients who experience relapse generally have a very poor prognosis. Therefore, novel approaches using targeted therapies to reduce toxicities and improve outcomes in the relapse setting are needed. The addition of rituximab, a monoclonal antibody against CD20, to upfront therapy has improved survival outcomes for high-risk patients and may allow decreased total chemotherapy in those with low-risk disease. Antibody-drug conjugates have been combined with chemotherapy in relapsed/refractory (R/R) NHL, and multiple antibody-drug conjugates are in development. Additionally, bispecific T-cell-engaging antibody constructs and autologous CAR T-cells have been successful in the treatment of R/R acute leukemias and are now being applied to R/R B-NHL with some successes. PD-L1 and PD-L2 on tumor cells can be targeted with checkpoint inhibitors, which restore T-cell-mediated immunity and antitumor responses and can be added to conventional chemotherapy and immune-directed therapies to augment responses. Lastly, trials of small molecule inhibitors targeting cell signaling pathways in NHL subtypes are underway. This article reviews many of the targeted therapies under development that could be considered for future trials in R/R pediatric mature B-NHL.

Pediatric Aggressive Mature B-Cell Lymphomas, Version 2.2020, NCCN Clinical Practice Guidelines in Oncology.

Pediatric aggressive mature B-cell lymphomas are the most common types of non-Hodgkin lymphoma in children, and they include Burkitt lymphoma (BL) and diffuse large B-cell lymphoma (DLBCL). These diseases are highly aggressive but curable, the treatment is complex, and patients may have many complicated supportive care issues. The NCCN Guidelines for Pediatric Aggressive Mature B-Cell Lymphomas provide guidance regarding pathology and diagnosis, staging, initial treatment, disease reassessment, surveillance, therapy for relapsed/refractory disease, and supportive care for clinicians who treat sporadic pediatric BL and DLBCL.

Novel targeted therapeutic agents for the treatment of childhood, adolescent and young adult non-Hodgkin lymphoma.

Non-Hodgkin lymphomas (NHLs) are a heterogeneous group of malignancies. Most NHLs in children, adolescent and young adult patients are aggressive lymphomas that are generally treated with multi-agent chemotherapy or immunochemotherapy regimens. While overall survival is high, the treatment can lead to a high rate of acute and long-term toxicity. However, in the rarer instance of relapsed or refractory disease, outcomes are dismal. Novel therapeutic approaches to the treatment of both T-cell and B-cell NHLs are critical to improve outcomes while also minimising the associated toxicity of current treatment regimes. Potential therapeutic approaches in development include humoral and cellular immunotherapies, small molecule inhibitors of relevant signalling pathways and epigenetic modifying agents. In this review, we will highlight the current state of development of agents of interest with a focus on agents relevant to childhood, adolescent and young adult NHL.

Pevonedistat, a NEDD8-activating enzyme inhibitor, is active in mantle cell lymphoma and enhances rituximab activity in vivo.

Mantle cell lymphoma (MCL) is characterized by an aggressive clinical course and inevitable development of refractory disease, stressing the need to develop alternative therapeutic strategies. To this end, we evaluated pevonedistat (MLN4924), a novel potent and selective NEDD8-activating enzyme inhibitor in a panel of MCL cell lines, primary MCL tumor cells, and 2 distinct murine models of human MCL. Pevonedistat exposure resulted in a dose-, time-, and caspase-dependent cell death in the majority of the MCL cell lines and primary tumor cells tested. Of interest, in the MCL cell lines with lower half-maximal inhibitory concentration (0.1-0.5 µM), pevonedistat induced G1-phase cell cycle arrest, downregulation of Bcl-xL levels, decreased nuclear factor (NF)-κB activity, and apoptosis. In addition, pevonedistat exhibited additive/synergistic effects when combined with cytarabine, bendamustine, or rituximab. In vivo, as a single agent, pevonedistat prolonged the survival of 2 MCL-bearing mouse models when compared with controls. Pevonedistat in combination with rituximab led to improved survival compared with rituximab or pevonedistat monotherapy. Our data suggest that pevonedistat has significant activity in MCL preclinical models, possibly related to effects on NF-κB activity, Bcl-xL downregulation, and G1 cell cycle arrest. Our findings support further investigation of pevonedistat with or without rituximab in the treatment of MCL.

Outcomes of adults and children with primary mediastinal B-cell lymphoma treated with dose-adjusted EPOCH-R.

Treatment with dose-adjusted EPOCH (etoposide, doxorubicin, cyclophosphamide, vincristine, prednisone) chemotherapy and rituximab (DA-EPOCH-R) has become the standard of care for primary mediastinal B-cell lymphoma (PMBCL) at many institutions despite limited data in the multi-centre setting. We report a large, multi-centre retrospective analysis of children and adults with PMBCL treated with DA-EPOCH-R to characterize outcomes and evaluate prognostic factors. We assessed 156 patients with PMBCL treated with DA-EPOCH-R across 24 academic centres, including 38 children and 118 adults. All patients received at least one cycle of DA-EPOCH-R. Radiation therapy was administered in 14·9% of patients. With median follow-up of 22·6 months, the estimated 3-year event-free survival (EFS) was 85·9% [95% confidence interval (CI) 80·3-91·5] and overall survival was 95·4% (95% CI 91·8-99·0). Outcomes were not statistically different between paediatric and adult patients. Thrombotic complications were reported in 28·2% of patients and were more common in paediatric patients (45·9% vs. 22·9%, P = 0·011). Seventy-five per cent of patients had a negative fluorodeoxyglucose positron emission tomography (FDG-PET) scan at the completion of DA-EPOCH-R, defined as Deauville score 1-3. Negative FDG-PET at end-of-therapy was associated with improved EFS (95·4% vs. 54·9%, P < 0·001). Our data support the use of DA-EPOCH-R for the treatment of PMBCL in children and adults. Patients with a positive end-of-therapy FDG-PET scan have an inferior outcome.

Immunotherapeutic approaches for the treatment of childhood, adolescent and young adult non-Hodgkin lymphoma.

With the introduction of the anti-CD20 monoclonal antibody rituximab, B-cell non-Hodgkin lymphoma was the first malignancy successfully treated with an immunotherapeutic agent. Since then, numerous advances have expanded the repertoire of immunotherapeutic agents available for the treatment of a variety of malignancies, including many lymphoma subtypes. These include the introduction of monoclonal antibodies targeting a variety of cell surface proteins, including the successful targeting of immunoregulatory checkpoint receptors present on T-cells or tumour cells. Additionally, cellular immunotherapeutic approaches utilize T- or Natural Killer-cells generated with chimeric antigen receptors against cell surface proteins or Epstein-Barr virus-associated latent membrane proteins. The following review describes the current state of immunotherapy for non-Hodgkin lymphoma including a summary of currently available data and promising agents currently in clinical development with future promise in the treatment of childhood, adolescent and young adult non-Hodgkin lymphoma.

The Incidence of Hypersensitivity Reactions to Pegylated Asparaginase in Children With Acute Lymphoblastic Leukemia: A City-wide Experience.

Asparaginase (ASNase) is an imperative component of pediatric acute lymphoblastic leukemia (ALL) therapy. Pegylating the ASNase extends its biological half-life in vivo and has become the only ASNase available in the United States for frontline therapy of ALL and lymphoblastic lymphoma. It is either infused intravenously (IV) or injected intramuscularly (IM), administrations of which are associated with hypersensitivity reaction ranging from localized skin reaction to severe anaphylaxis. A retrospective review of 96 medical records of pediatric ALL patients was performed. We compared the incidence of hypersensitivity reaction associated with IV versus IM administration of pegylated ASNase. Ninety-one patients were included in the final analysis; 31 having received pegylated ASNase IV and 60 receiving it IM. The incidence of any grade ≥ 2 hypersensitivity reaction in patients who received IV ASNase was 32.2% compared with 13.3% in the IM group (P=0.032). There was no difference in higher grade hypersensitivity reactions (19.4% vs. 11.7%). Most reactions tended to occur during periods of leukemia therapy that did not include concomitant steroid therapy. Our retrospective analysis indicates that IV administration of pegylated ASNase increases the incidence of low-grade, but not grade 3-4, hypersensitivity reactions compared with IM administration.

Obinutuzumab (GA101) compared to rituximab significantly enhances cell death and antibody-dependent cytotoxicity and improves overall survival against CD20(+) rituximab-sensitive/-resistant Burkitt lymphoma (BL) and precursor B-acute lymphoblastic leukaemia (pre-B-ALL): potential targeted therapy in patients with poor risk CD20(+) BL and pre-B-ALL.

Obinutuzumab is a novel glycoengineered Type-II CD20 monoclonal antibody. CD20 is expressed in approximately 100% of children and adolescents with Burkitt lymphoma (BL) and 40% with precursor B-cell acute lymphoblastic leukaemia (pre-B-ALL). We evaluated the anti-tumour activity of obinutuzumab versus rituximab against rituximab-resistant (Raji 4RH) and -sensitive (Raji) BL and pre-B-ALL (U698-M) cells in vitro and in human BL or Pre-B-ALL xenografted mice. We demonstrated that obinutuzumab compared to rituximab significantly enhanced cell death against Raji 35·6 ± 3·1% vs. 25·1 ± 2·0%, (P = 0·001), Raji4RH 19·7 ± 2·2% vs. 7·9 ± 1·5% (P = 0·001) and U-698-M 47·3 ± 4·9% vs. 23·2 ± 0·5% (P = 0·001), respectively. Obinutuzumab versus rituximab also induced a significant increase in antibody-dependent cellular cytotoxicity (ADCC) with K562-IL15-41BBL expanded NK cells against Raji 73·8 ± 8·1% vs. 56·81 ± 4·6% (P = 0·001), Raji-4RH 40·0 ± 1·6% vs. 0·5 ± 1·1% (P = 0·001) and U-698-M 70·0 ± 1·6% vs. 45·5 ± 0·1% (P = 0·001), respectively. Overall survival in tumour xenografted mice receiving 30 mg/kg of obinutuzumab was significantly increased when compared to those receiving 30 mg/kg of rituximab in BL; Raji (P = 0·05), Raji4RH (P = 0·02) and U698-M (P = 0·03), respectively. These preclinical data suggest obinutuzumab is significantly superior to rituximab in inducing cell death, ADCC and against rituximab-sensitive/-resistant BL and pre-B-ALL xenografted mice. Taken together, these preclinical results provide evidence to suggest that future investigation of obinutuzumab is warranted in patients with relapsed/refractory CD20(+) BL and/or pre-B-ALL.

Entinostat, a novel histone deacetylase inhibitor is active in B-cell lymphoma and enhances the anti-tumour activity of rituximab and chemotherapy agents.

Histone deacetylases (HDACs) inhibitors are active in T-cell lymphoma and are undergoing pre-clinical and clinical testing in other neoplasms. Entinostat is an orally bioavailable class I HDAC inhibitor with a long half-life, which is under evaluation in haematological and solid tumour malignancies. To define the activity and biological effects of entinostat in B-cell lymphoma we studied its anti-tumour activity in several rituximab-sensitive or -resistant pre-clinical models. We demonstrated that entinostat is active in rituximab-sensitive cell lines (RSCL), rituximab-resistant cell lines (RRCL) and primary tumour cells isolated from lymphoma patients (n = 36). Entinostat exposure decreased Bcl-XL (BCL2L1) levels and induced apoptosis in cells. In RSCL and RRCL, entinostat induced p21 (CDKN1A) expression leading to G1 cell cycle arrest and exhibited additive effects when combined with bortezomib or cytarabine. Caspase inhibition diminished entinostat activity in some primary tumour cells suggesting that entinostat has dual mechanisms-of-action. In addition, entinostat increased the expression of CD20 and adhesion molecules. Perhaps related to these effects, we observed a synergistic activity between entinostat and rituximab in a lymphoma-bearing severe combined immunodeficiency (SCID) mouse model. Our data suggests that entinostat is an active HDAC inhibitor that potentiates rituximab activity in vivo and supports its further clinical development in B-cell lymphoma.

Impact of persistent minimal residual disease post-consolidation therapy in children and adolescents with advanced Burkitt leukaemia: a Children's Oncology Group Pilot Study Report.

Patient-specific primers from 10 children/adolescents with Burkitt leukaemia (BL) ± central nervous system disease who were treated with French-British-American/Lymphome Malins de Burkitt 96 C1 plus rituximab were developed from diagnostic blood/bone marrow. Minimal residual disease (MRD) was assessed by real-time polymerase chain reaction at the end of induction (EOI) and consolidation (EOC). Seventy per cent (7/10) and 71% (5/7) were MRD-positive at EOI and EOC, respectively, with no disease recurrences. MRD after induction and consolidation did not predict relapse and subsequent therapy appeared to eliminate MRD. Thus, assessing MRD at a later time point is warranted in future trials to determine its clinical significance.

Rituximab with chemotherapy in children and adolescents with central nervous system and/or bone marrow-positive Burkitt lymphoma/leukaemia: a Children's Oncology Group Report.

Children and adolescents with Burkitt Lymphoma (BL) and combined central nervous system (CNS) and bone marrow involvement still have a poor prognosis with chemotherapy alone. We therefore investigated in children and adolescents with bone marrow (≥25% blasts) and/or CNS-positive Burkitt lymphoma the chemoimmunotherapy combination of rituximab (375 mg/m(2) ) and the standard chemotherapy arm of our previously reported French-American-British (FAB) Lymphome Malins de Burkitt (LMB) 96 trial. Central pathological and cytogenetic characterization was also performed. There were 40 evaluable patients with Burkitt histology (25 with leukaemia and 15 with CNS disease ± leukaemia). The chemoimmunotherapy regimen was well tolerated. The incidence of grade III/IV mucositis during induction cycles with combined chemotherapy and rituximab was 31% and 26%, respectively. The 3-year event-free survival (EFS)/overall survival (OS) was 90% (95% confidence interval [CI], 76-96%) in the entire cohort and 93% (95% CI, 61-99%) in patients with CNS disease. Based on the results of this trial, an international randomized study of FAB/LMB 96 chemotherapy ± rituximab for high-risk patients is currently under investigation.

Rituximab pharmacokinetics in children and adolescents with de novo intermediate and advanced mature B-cell lymphoma/leukaemia: a Children's Oncology Group report.

The ANHL01P1 trial was undertaken to determine pharmacokinetics and safety following the addition of rituximab to French-American-British/Lymphome Malins de Burkitt (FAB/LMB96) chemotherapy in 41 children and adolescents with Stage III/IV mature B-cell lymphoma/leukaemia. Patients received rituximab (375 mg/m(2) ) days -2 and 0 of two induction cycles and day 0 of two consolidation cycles. Highest peak levels were achieved following the second dose of each induction cycle [299 ± 19 and 384 ± 25 µg/ml (Group-B); 245 ± 31 and 321 ± 32 µg/ml (Group-C)] with sustained troughs and t½ of 26-29 d. Rituximab can be safely added to FAB chemotherapy with high early rituximab peak/trough levels and a long t½.

Ofatumumab: a novel, fully human anti-CD20 monoclonal antibody for the treatment of chronic lymphocytic leukemia.

Ofatumumab is a fully human, IgG anti-CD20 monoclonal antibody codeveloped by GlaxoSmithKline (Brentford, UK) and Genmab (Copenhagen, Denmark). In preclinical studies, ofatumumab exhibited more potent in vitro activity than rituximab against B-cell malignancies and prolonged survival in in vivo animal models compared with rituximab. Ofatumumab is clinically well tolerated with initial infusion reactions being the predominant associated toxicity. Ofatumumab has demonstrated efficacy in relapsed/refractory chronic lymphocytic leukemia (CLL) and has received regulatory approval in both Europe and the USA for treatment of fludarabine and alemtuzumab refractory disease. Single-agent ofatumumab has resulted in overall response rates of 42-51% in relapsed/refractory CLL and up to 80% when combined with chemotherapy. In de novo CLL, overall response rates of 77-78% have been achieved.

AMG176, an MCL-1 inhibitor, is active in pre-clinical models of aggressive B-cell lymphomas.

Upregulation of the anti-apoptotic protein MCL-1 has been implicated in chemotherapy resistance and poor clinical outcomes in B-cell lymphoma (BCL). We report the activity of AMG176, a direct, selective MCL-1 inhibitor, in preclinical models of BCL. A panel of cell lines representing diffuse large B-cell lymphoma (DLBCL), double-hit lymphoma (DHL) and Burkitt's lymphoma (BL) was selected. AMG176 induced apoptotic cell death in a dose- and time-dependent manner in all BCL cell lines. Baseline MCL-1 expression was not predictive of response. AMG176 exhibited impressive synergy with venetoclax and chemotherapeutic agents, less so with proteasomal inhibitors, and antagonism with anti-CD20 monoclonal antibodies. The activity of AMG176 could not be confirmed in murine models of BCL. Combination therapy targeting MCL-1 and BCL-2 may provide an alternative therapeutic approach in BCL, however optimal patient selection will remain the key to obtaining high response rates and tolerability.

Molecular Evolution of Classic Hodgkin Lymphoma Revealed Through Whole-Genome Sequencing of Hodgkin and Reed Sternberg Cells.

The rarity of malignant Hodgkin and Reed Sternberg (HRS) cells in classic Hodgkin lymphoma (cHL) limits the ability to study the genomics of cHL. To circumvent this, our group has previously optimized fluorescence-activated cell sorting to purify HRS cells. Using this approach, we now report the whole-genome sequencing landscape of HRS cells and reconstruct the chronology and likely etiology of pathogenic events leading to cHL. We identified alterations in driver genes not previously described in cHL, APOBEC mutational activity, and the presence of complex structural variants including chromothripsis. We found that high ploidy in cHL is often acquired through multiple, independent chromosomal gains events including whole-genome duplication. Evolutionary timing analyses revealed that structural variants enriched for RAG motifs, driver mutations in B2M, BCL7A, GNA13, and PTPN1, and the onset of AID-driven mutagenesis usually preceded large chromosomal gains. This study provides a temporal reconstruction of cHL pathogenesis. SIGNIFICANCE: Previous studies in cHL were limited to coding sequences and therefore not able to comprehensively decipher the tumor complexity. Here, leveraging cHL whole-genome characterization, we identify driver events and reconstruct the tumor evolution, finding that structural variants, driver mutations, and AID mutagenesis precede chromosomal gains. This article is highlighted in the In This Issue feature, p. 171.

The future role of monoclonal antibody therapy in childhood acute leukaemias.

Leukaemia is the single most common childhood malignancy. With modern treatment regimens, survival in acute lymphoblastic leukaemia (ALL) approaches 90%. Only about 70% of children with acute myeloid leukaemia (AML) achieve long term survival. Patients who relapse have a dismal prognosis. Novel therapeutic approaches are needed to improve treatment outcomes in newly-diagnosed patients with a poor prognosis and for patients with relapsed/refractory disease that have limited treatment options. One promising approach in treating haematological malignancies has been the use of monoclonal antibodies to target cell surface antigens expressed on malignant cells. Most success with monoclonal antibody therapy in the treatment of haematological malignancies has come in the setting of adult B-cell non-Hodgkin lymphoma with the addition of the anti-CD20 monoclonal antibody rituximab to standard treatment regimens. In order to further advance treatment of haematological malignancies, novel monoclonal antibodies continue to be developed that target a variety of cell surface antigens. Several antibodies continue to be investigated in childhood leukaemias. This review will discuss the development of monoclonal antibodies that target a variety of cell surface antigens for the treatment of childhood ALL and the use of the anti-CD33 antibody gemtuzumab ozogamicin in the treatment of childhood AML.