Thuan Chong Quah

Toward the Cure of All Children With Cancer Through Collaborative Efforts: Pediatric Oncology As a Global Challenge

Advances in the treatment of childhood cancers have resulted in part from the development of national and international collaborative initiatives that have defined biologic determinants and generated risk-adapted therapies that maximize cure while minimizing acute and long-term effects. Currently, more than 80% of children with cancer who are treated with modern multidisciplinary treatments in developed countries are cured; however, of the approximately 160,000 children and adolescents who are diagnosed with cancer every year worldwide, 80% live in low- and middle-income countries (LMICs), where access to quality care is limited and chances of cure are low. In addition, the disease burden is not fully known because of the lack of population-based cancer registries in low-resource countries. Regional and ethnic variations in the incidence of the different childhood cancers suggest unique interactions between genetic and environmental factors that could provide opportunities for etiologic research. Regional collaborative initiatives have been developed in Central and South America and the Caribbean, Africa, the Middle East, Asia, and Oceania. These initiatives integrate regional capacity building, education of health care providers, implementation of intensity-graduated treatments, and establishment of research programs that are adjusted to local capacity and local needs. Together, the existing consortia and regional networks operating in LMICs have the potential to reach out to almost 60% of all children with cancer worldwide. In summary, childhood cancer burden has been shifted toward LMICs and, for that reason, global initiatives directed at pediatric cancer care and control are needed. Regional networks aiming to build capacity while incorporating research on epidemiology, health services, and outcomes should be supported.

Thiopurine Methyltransferase polymorphisms in a multiracial Asian population and children with acute lymphoblastic leukemia

The purpose of this study was to determine the frequency of thiopurine methyltransferase (TPMT) polymorphisms in a multiracial Asian population and to assess its relevance in the management of childhood acute lymphoblastic leukemia (ALL). Six hundred unrelated cord blood samples from 200 Chinese, Malay, and Indian healthy newborns were collected at the National University Hospital, Singapore; an additional 100 children with ALL were analyzed for five of the commonly reported TPMT variant alleles using polymerase chain reaction/restriction fragment length polymorphism and allele-specific polymerase chain reaction-based assays. In the cord blood study, the TPMT *3C variant was detected in all three ethnic groups; Chinese, Malays, and Indians had allele frequencies of 3%, 2.3%, and 0.8%, respectively. The TPMT *3A variant was found only among the Indians at a low allele frequency of 0.5%. The TPMT *6 variant was found in one Malay sample. Among the children with ALL, two white and one Chinese were heterozygous for the TPMT *3A variant and showed intermediate sensitivity to 6-mercaptopurine during maintenance therapy. Three Chinese patients and one Malay patient were heterozygous for the TPMT *3C variant. Mercaptopurine sensitivity could be validated in only one out of four TPMT *3C heterozygous patients. The overall allele frequency of the TPMT variants in this multiracial population was 2.5%. The TPMT *3C was the most common variant allele;TPMT *3A and TPMT *6 were rare. These results support the feasibility of performing TPMT genotyping in all children diagnosed with acute leukemia to minimize toxicity from thiopurine chemotherapy.

Minimal Residual Disease–Guided Treatment Deintensification for Children With Acute Lymphoblastic Leukemia: Results From the Malaysia-Singapore Acute Lymphoblastic Leukemia 2003 Study

PURPOSE To improve treatment outcome for childhood acute lymphoblastic leukemia (ALL), we designed the Malaysia-Singapore ALL 2003 study with treatment stratification based on presenting clinical and genetic features and minimal residual disease (MRD) levels measured by polymerase chain reaction targeting a single antigen-receptor gene rearrangement. PATIENTS AND METHODS Five hundred fifty-six patients received risk-adapted therapy with a modified Berlin-Frankfurt-Münster-ALL treatment. High-risk ALL was defined by MRD ≥ 1 × 10(-3) at week 12 and/or poor prednisolone response, BCR-ABL1, MLL gene rearrangements, hypodiploid less than 45 chromosomes, or induction failure; standard-risk ALL was defined by MRD ≤ 1 × 10(-4) at weeks 5 and 12 and no extramedullary involvement or high-risk features. Intermediate-risk ALL included all remaining patients. RESULTS Patients who lacked high-risk presenting features (85.7%) received remission induction therapy with dexamethasone, vincristine, and asparaginase, without anthracyclines. Six-year event-free survival (EFS) was 80.6% ± 3.5%; overall survival was 88.4% ± 3.1%. Standard-risk patients (n = 172; 31%) received significantly deintensified subsequent therapy without compromising EFS (93.2% ± 4.1%). High-risk patients (n = 101; 18%) had the worst EFS (51.8% ± 10%); EFS was 83.6% ± 4.9% in intermediate-risk patients (n = 283; 51%). CONCLUSION Our results demonstrate significant progress over previous trials in the region. Three-drug remission-induction therapy combined with MRD-based risk stratification to identify poor responders is an effective strategy for childhood ALL.

Multiplex Minisequencing Screen for Common Southeast Asian and Indian β-Thalassemia Mutations

BACKGROUND Beta-thalassemia is endemic to many regions in Southeast Asia and India, and <20 beta-globin gene mutations account for > or =90% of beta-thalassemia alleles in these places. We describe a multiplex minisequencing assay to detect these common mutations. METHODS Gap-PCR was used to simultaneously amplify the beta-globin gene from genomic DNA and to detect the Delta619bp deletion mutation. Multiplex minisequencing was then performed on the amplified beta-globin fragment to detect an additional 15 common Southeast Asian and Indian beta-thalassemia mutations. Site-specific primers of different lengths were subjected to multiple rounds of annealing and single-nucleotide extension in the presence of thermostable DNA polymerase and the four dideoxynucleotides, each labeled with a different fluorophore. Minisequencing products were separated and detected by capillary electrophoresis, followed by automated genotyping. The optimized assay was subjected to a double-blind validation analysis of 89 beta-thalassemia and wild-type DNA samples of known genotype. RESULTS Homozygous wild-type or mutant DNA samples produced electropherograms containing only a single colored peak for each mutation site, whereas samples heterozygous for a specific mutation displayed two different-colored peaks for that mutation site. Samples were automatically genotyped based on color and position of primer peaks in the electropherogram. In the double-blind validation analysis, all 89 DNA samples were genotyped correctly (100% assay specificity). CONCLUSIONS The described semiautomated multiplex minisequencing assay can detect the most common Southeast Asian and Indian beta-thalassemia mutations, is amenable to high-throughput scale up, and may bring population-based screening of beta-thalassemia in endemic regions a step closer to implementation.

Ethnic differences in the frequency of subtypes of childhood acute lymphoblastic leukemia: results of the Malaysia-Singapore Leukemia Study Group.

Childhood acute lymphoblastic leukemia (ALL) is clinically heterogeneous with prognostically and biologically distinct subtypes. Although racial differences in frequency of different types of childhood ALL have been reported, many are confounded by selected or limited population samples. The Malaysia-Singapore (MA-SPORE) Leukemia Study Group provided a unique platform for the study of the frequency of major subgroups of childhood ALL in a large cohort of unselected multiethnic Asian children. Screening for the prognostically important chromosome abnormalities (TEL-AML1, BCR-ABL, E2A-PBX1, and MLL) using multiplex reverse-transcription polymerase chain reaction was performed on 299 consecutive patients with ALL at 3 study centers (236 de novo, 63 at relapse), with the ethnic composition predominantly Chinese (51.8%) and Malay (34.8%). Reverse-transcription polymerase chain reaction was successful in 278 (93%) of cases screened. The commonest fusion transcript was TEL-AML1 (19.1%) followed by BCR-ABL (7.8%), MLL rearrangements (4.2%), and E2A-PBX1 (3.1%). Chinese have a significantly lower frequency of TEL-AML1 (13.3% in de novo patients) compared with Malays (22.2%) and Indians (21.7%) (P=0.04). Malays have a lower frequency of T-ALL (6.2%) compared with the Chinese and Indians (9.8%). Both Malays (7.4%) and Chinese (5.0%) have significantly higher frequency of BCR-ABL compared with the Indian population (P<0.05) despite a similar median age at presentation. Our study suggests that there are indeed significant and important racial differences in the frequency of subtypes of childhood ALL. Comprehensive subgrouping of childhood ALL may reveal interesting population frequency differences of the various subtypes, their risk factors and hopefully, its etiology.

Diagnostic delay in pediatric solid tumors: A population based study on determinants and impact on outcomes

Despite socioeconomic and clinical progress, pediatric tumors continue to present in advanced stage, and may be due to delays in diagnosis. This study aimed to identify factors associated with diagnostic delay (time between symptom onset and diagnosis) in pediatric tumors in a population‐based study, and to assess the impact of delay on subsequent outcome.

Mitochondrial D-loop polymorphisms and mitochondrial DNA content in childhood acute lymphoblastic leukemia.

The mitochondrial displacement loop (D-loop) controls mitochondrial expression, with mutations and mitochondrial DNA (mtDNA) content linked to oncogenesis. We investigated D-loop polymorphisms and mtDNA content in childhood acute lymphoblastic leukemia (ALL). The D-loop was sequenced in 251 children: precursor B ALL (n=114), with 76 paired remission/relapse samples; T-ALL (n=24); cord blood controls (n=113). The mtDNA copy number was analyzed using real-time quantitative polymerase chain reaction for 92 controls and 54 ALL patients at diagnosis and remission. Polymorphisms around H-strand replication origin (nucleotides 150 to 199) and conserved sequence block II (nucleotides 299 to 317) were associated with leukemia biology and treatment response. T-ALL patients were more likely to have longer nt303 poly-C tract. T199C polymorphism was associated with increased risk of ALL in Malays; T152C was more frequent in good responders. There was no difference in mtDNA content between diagnostic ALL samples and controls; however, there was significant decrease in mtDNA content after treatment, especially in samples with OH polymorphisms. Somatic mutations were found in 13% (9 of 76) of patients, suggesting a link to leukemogenesis. Our results suggest that polymorphisms impacting transcriptional control could affect mtDNA replication. Decrease in mtDNA content after treatment may confer susceptibility to chemotherapy and be a clue to the good prognosis of childhood ALL.

Epstein–Barr virus-associated T/natural killer-cell lymphoproliferative disorder in children and young adults has similar molecular signature to extranodal nasal natural killer/T-cell lymphoma but shows distinctive stem cell-like phenotype

We performed gene expression profiling in Epstein–Barr virus (EBV)-associated T/natural killer (NK)-cell lymphoproliferative disorder in children and young adults (TNKLPDC) in order to understand the molecular pathways deregulated in this disease and compared it with nasal-type NK/T-cell lymphoma (NKTL). The molecular and phenotypic signature of TNKLPDC is similar to NKTL, with overexpression of p53, survivin and EZH2. Down-regulation of EZH2 in TNKLPDC cell lines led to an increase in apoptosis and decrease in tumor viability, suggesting that EZH2 may be important for the survival of TNKLPDC cells and hence potentially a useful therapeutic target. Notably, our gene expression profiling revealed a distinctive enrichment of stem cell related genes in TNKLPDC compared to NKTL. This was validated by a significantly higher expression of aldehyde dehydrogenase 1 (ALDH1) in TNKLPDC cell lines compared to NKTL cell lines. The novel discovery of cancer stem cell properties in TNKLPDC has potential therapeutic implications in this group of disorders.

Oral refeeding following acute gastro-enteritis a clinical trial using four refeeding regimes

A clinical trial using four different oral refeeding regimes was conducted in 100 patients following acute gastro-enteritis. There was no difference in terms of the diarrhoea-relapse rates among the four groups of patients. However, a better weight gain was recorded in the groups using a lactose-free soy formula and a low-lactose low-fat cows milk formula.

Mutations in the SRP54 gene cause severe congenital neutropenia as well as Shwachman-Diamond–like syndrome

Congenital neutropenias (CNs) are rare heterogeneous genetic disorders, with about 25% of patients without known genetic defects. Using whole-exome sequencing, we identified a heterozygous mutation in the SRP54 gene, encoding the signal recognition particle (SRP) 54 GTPase protein, in 3 sporadic cases and 1 autosomal dominant family. We subsequently sequenced the SRP54 gene in 66 probands from the French CN registry. In total, we identified 23 mutated cases (16 sporadic, 7 familial) with 7 distinct germ line SRP54 mutations including a recurrent in-frame deletion (Thr117del) in 14 cases. In nearly all patients, neutropenia was chronic and profound with promyelocytic maturation arrest, occurring within the first months of life, and required long-term granulocyte colony-stimulating factor therapy with a poor response. Neutropenia was sometimes associated with a severe neurodevelopmental delay (n = 5) and/or an exocrine pancreatic insufficiency requiring enzyme supplementation (n = 3). The SRP54 protein is a key component of the ribonucleoprotein complex that mediates the co-translational targeting of secretory and membrane proteins to the endoplasmic reticulum (ER). We showed that SRP54 was specifically upregulated during the in vitro granulocytic differentiation, and that SRP54 mutations or knockdown led to a drastically reduced proliferation of granulocytic cells associated with an enhanced P53-dependent apoptosis. Bone marrow examination of SRP54-mutated patients revealed a major dysgranulopoiesis and features of cellular ER stress and autophagy that were confirmed using SRP54-mutated primary cells and SRP54 knockdown cells. In conclusion, we characterized a pathological pathway, which represents the second most common cause of CN with maturation arrest in the French CN registry.