Do mutations at the glycophorin A locus in patients treated for childhood Hodgkin's disease predict secondary leukaemia?

Treatment-related myelodysplastic syndrome/acute myeloid leukemia in survivors of childhood cancer--an update

Treatment-related myelodysplastic syndrome/acute myeloid leukemia (t-MDS/t-AML) is a devastating complication of treatment for childhood cancer. However, the major cause of premature death of children treated for cancer remains their primary cancer. The understanding of the presentation, incidence, predisposing risk factors and pathobiology of t-MDS/t-AML is increasing. This increased understanding has not yet been translated into improved outcomes of therapy for t-MDS/t-AML. However, newer approaches are under study.

Polymorphisms of drug metabolizing enzymes and markers of genotoxicity to identify patients with Hodgkin's lymphoma at risk of treatment-related complications

Survivors of childhood Hodgkin's lymphoma (HL) have an increased risk of developing treatment-related complications, especially second malignant neoplasms, as a result of treatment regimens incorporating chemotherapy and radiation therapy. Second cancers include leukemias that generally occur in the first two decades after therapy, and adult-type solid tumors that generally exhibit continued increasing incidence throughout subsequent follow-up. Identified clinical risk factors for second cancers include age at the time of treatment and intensity and type of therapy, with particularly strong associations between the use of radiotherapy and subsequent breast cancer, and alkylator chemotherapy dose-intensity and risk of secondary leukemia. However, second cancers affect a minority of patients, and there is probably great variability in individual susceptibility for this complication. Common genetic polymorphisms in drug-metabolizing enzymes that result in impaired detoxification of chemotherapy or inefficient repair of drug- or radiation-induced genetic damage may lead to increased risk of a second cancer. Studies of the potential role of polymorphisms in the genes encoding the glutathione S-transferases, cytochrome P450 3A4, NAD(P)H:quinone oxidoreductase and myeloperoxidase in the etiology of treatment-related complications are reviewed. Biological markers of drug- and radiation-induced genetic damage may also identify patients at higher risk of immediate and delayed side effects of therapy. The Children's Oncology Group (COG) is examining the roles of polymorphisms in drug metabolizing enzymes and biological markers of genotoxicity in predicting the treatment-related outcomes of patients with HL. These investigations may ultimately allow the use of pharmacogenetically guided therapy to improve the outcome of HL therapy and reduce the risk of therapy-related complications, especially secondary malignancies.

Pregnancy outcome after treatment for Wilms tumor: a report from the National Wilms Tumor Study Group

PURPOSE

This study was undertaken to determine the effect, if any, of prior treatment with radiation therapy or chemotherapy for Wilms tumor diagnosed during childhood or adolescence on live births, birthweight, and the frequency of congenital malformations.

PATIENTS AND METHODS

We reviewed pregnancy outcomes among survivors of Wilms tumor treated with or without irradiation to the flank or tumor bed on National Wilms Tumor Studies 1, 2, 3, and 4 using a maternal questionnaire and review of both maternal and offspring medical records.

RESULTS

We received reports regarding 427 pregnancies with duration of 20 weeks or longer, including 409 liveborn singletons for whom 309 sets of medical records were reviewed. Malposition of the fetus and early or threatened labor were more frequent among irradiated women. Both were more frequent among women who received higher radiation therapy doses. The offspring of the irradiated female patients were more likely to weigh less than 2,500 g at birth and to be of less than 36 weeks gestation, with both being more frequent after higher doses of radiation. An increased percentage of offspring of irradiated females had one or more congenital malformations.

CONCLUSION

Women who receive flank radiation therapy as part of their treatment for Wilms tumor are at increased risk of fetal malposition and premature labor. The offspring of these women are at risk for low birthweight, premature (< 36 weeks gestation) birth, and the occurrence of congenital malformations. These risks must be considered in the obstetrical management of female survivors of Wilms tumor.

Genetic predisposition and treatment-related leukemia

Treatment-related leukemias are one of the most devastating late complications of cancer therapy. Patients with rare cancer predisposition syndromes including neurofibromatosis type 1 and inherited p53 mutations are at an increased risk for this complication. Other patients may have increased susceptibility because they possess common genetic polymorphisms in drug-metabolizing enzymes that result in impaired detoxification of chemotherapy or inefficient repair of drug-induced genetic damage. We review studies that have identified a potential role for polymorphisms in the genes encoding the glutathione-S-transferases (GSTs), NAD(P) H: quinone oxidoreductase, myeloperoxidase, N-acetyltransferase (NATs), cytochrome P450 (CYP) 1A1 and 3A4, methylenetetrahydrofolate reductase (MTHFR), cystathionine-beta-synthase (CBS), and others in the etiology of primary or secondary acute leukemias, and therapy-related complications. The identification of high risk polymorphisms and use of pharmacogenetically-guided therapies holds promise to improve the outcome of cancer therapy and reduce the risk of treatment-related leukemias.

Therapy related leukemias: susceptibility, prevention and treatment

Acute leukemia is the most frequent therapy-related malignancy. Together with the increasing use of chemo- and radiotherapy, individual predisposing factors play a key role. Most of secondary leukemias can be divided in two well-defined groups: those secondary to the use of alkylating agents and those associated to topoisomerase inhibitors. Leukemias induced by alkylating agents usually follow a long period of latency from the primary tumour and present as myelodysplasia with unbalanced chromosomal aberrations. These frequently include deletions of chromosome 13 and loss of the entire or of part of chomosomes 5 or 7. The loss of the coding regions for tumor suppressor genes from hematopoietic progenitor cells is a particularly unfavourable event, since the remaining allele becomes susceptible to inactivating mutations leading to the leukemic transformation. The tumorigenic action of topoisomerase inhibitors is on the other hand due to the formation of multiple DNA strand breaks, resolved by chromosomal translocations. Among these, chromosome 11, band q23, where the myeloid-lymphoid leukemia (MLL) gene is located, is often involved. Frequent partners are chromosomes 9, 19 and 4 in the t(9;11), t(19;11) and t(4;11) translocations. Younger age, a mean period of latency of 2 years and monocytic subtypes are characteristic features of this type of leukemia. Among patients at risk for secondary leukemia, those with Hodgkin's disease are the most extensively studied, with the major impact of alkylating agents included in the chemotherapy schedule. The same is true for non-Hodgkin's lymphoma, while in multiple myeloma and acute lymphoblastic leukemia determinants are the dose of melphalan and of epypodophyllotoxin, respectively. Patients with breast, ovarian and testicular neoplasms are also at risk, in particular if trated with the association of alkylating agents and topoisomerase II inhibitors. According to the EBMT registry, in patients with lymphoma treated with high-dose therapy and autologous stem cell transplantation the cumulative risk of inducing leukemia at 5 years is 2.6%. Among treatment options, supportive therapy is indicated in older patients, while allogeneic stem cell transplantation, related or matched-unrelated, is feasible in younger patients. These data indicate the need for the identification of predisposing factors for secondary leukemia. In particular, frequent follow-up of patients at high-risk should be performed and any peripheral blood cytopenia should be considered suspicious. Whenever possible, the exclusion of drugs known to be leukemogenic from the treatment schedules should be considered, especially in young patients.

Pregnancy outcome in long-term survivors of childhood cancer

BACKGROUND

By the year 2010, 1/250 young adults will be long-term survivors of childhood cancer. One of the major concerns is whether they will be able to have healthy children.

PROCEDURE

The literature was reviewed to determine 1) the extent of intrapartum and perinatal complications experienced by survivors or their spouses and 2) the risk of congenital malformations or cancer in their children.

RESULTS AND CONCLUSIONS

Series have reported on pregnancy complications among approximately 400 female survivors and 300 partners of male survivors. An increased incidence of spontaneous abortions, low-birth-weight babies, and neonatal deaths has been described for women with Wilms tumor who had received at least 20 Gy abdominal radiation. Hodgkin disease survivors who had received both radiation and chemotherapy (but not either alone) also appear to be at increased risk of spontaneous abortions. Based on several thousand survivor offspring, there is no overall increased risk of either congenital malformations or childhood cancer. Further studies will define the outcome of offspring of cancer survivors treated in the modern era.

Evaluation of mutant frequencies at the hprt and the T-cell receptor loci in pediatric cancer patients before treatment

Mutant frequencies (Mfs) at the two genetic loci, the hypoxanthine phosphoribosyl transferase (hprt) gene and the T-cell receptor (TCR) gene were evaluated in pediatric cancer patients before starting chemotherapy or radiotherapy. The study population consisted of 27 patients with various solid tumors (mean age +/- SD; 5.5 +/- 5.1 years, range; 0.2-14.5 years), 5 patients with acute leukemia (10.3 +/- 6.1, 1.3-17.0 years), and 26 healthy controls (11.6 +/- 4.0, 4.4-22.2 years). Although the age distributions were different, the mean Mf values of the hprt and the TCR loci were comparable among these three groups. On an individual basis taking the age factor into consideration, the hprt-Mfs of 3 patients with solid tumors, i.e., two patients with Hodgkin's disease and one patient with Askin tumor, were found to be well above the 95% confidence limit. There were no patients with a TCR-Mf exceeding the 95% confidence limit. These data suggest the possibility that some patients with solid tumors may be predisposed to mutational susceptibility before treatment. The assay of the hprt-Mf appears more sensitive than the TCR-Mf assay in distinguishing these patients.

Molecular epidemiology of hematological neoplasms--present status and future directions

The field of molecular epidemiology, using modern epidemiological approaches and taking the advantage of the advances in molecular biology can provide new tools for the exploration of etiological determinants, either environmental or hereditary, in the development of hematological neoplasms. It is now possible to identify some host susceptibility characteristics, to measure the effective dose of exposure, and to identify early, pre-clinical biological effects, using sensitive and specific biomarkers. The significant variation in the incidence of hematological neoplasms in different geographical areas, races, and age groups, the high rates of familial aggregation in certain populations, the involvement of protooncogenes and tumor suppressor genes in the development of hematological neoplasms, as well as of many environmental agents such as chemicals, radiation, and viruses, support the important role of molecular epidemiology in the investigation of the development of hematological neoplasms.

Genetic instability in patients with Hodgkin's disease undergoing chemotherapy

We have studied the effect of chemotherapy on the level of a particular kind of genetic instability in patients with Hodgkin's disease. The particular type of genetic instability assayed is exemplified by trans-rearrangements between two (rather than within one) T cell antigen receptor. 16 patients were studied during their course of treatment. Presentation samples were available for 13 of these patients; 9 of them showed an increase in the level of trans-rearrangements during their exposure to chemotherapeutic agents (P < 0.043). All patients for whom posttherapy samples were available (10 out of 16) showed a return to baseline levels of trans-rearrangements 1-5 mo after completion of therapy (P < 0.03). Thus, this assay appears to be a marker for the "destabilizing" effects of certain chemotherapeutic agents.

Neonatal vitamin K administration and in vivo somatic mutation

The glycophorin A (GPA) mutation assay was used to examine the risk of in vivo somatic mutation in infants following neonatal administration of vitamin K. The assay assesses damage to erythroid stem cells by measuring the frequency of NO and NN variant red cells of MN blood group heterozygotes using FACS analysis. Blood samples were obtained from 178 infants aged between 10 and 183 days. Twenty-six children were excluded from study having received a blood transfusion. Sixty-four of the remaining 152 infants were of the MN phenotype, samples from whom were analysed using the assay system, providing the first data of NO and NN variant frequencies (vfs) in children aged less than 1 year. Twenty of these 64 infants received vitamin K orally (group A), 17 intramuscularly (group B) and 25 intravenously (group C). Results were compared with those from a reference population of children aged 1-15 years. There were no significant differences in NO, NN and total vf between any of groups A, B and C. For all groups both NO and total vf were significantly lower than those for the control population. This result is of some interest and clearly warrants further investigation. NN and total vfs were greater than the 95th percentile for the pooled data from groups A, B and C in three instances, one in each group. It was thus not possible to demonstrate an association between the route of vitamin K administration and an increase in mutation at the GPA locus.

Benzene induces gene-duplicating but not gene-inactivating mutations at the glycophorin A locus in exposed humans

Occupational exposure to benzene is known to cause leukemia, but the mechanism remains unclear. Unlike most other carcinogens, benzene and its metabolites are weakly or nonmutagenic in most simple gene mutation assays. Benzene and its metabolites do, however, produce chromosomal damage in a variety of systems. Here, we have used the glycophorin A (GPA) gene loss mutation assay to evaluate the nature of DNA damage produced by benzene in 24 workers heavily exposed to benzene and 23 matched control individuals in Shanghai, China. The GPA assay identifies stem cell or precursor erythroid cell mutations expressed in peripheral erythrocytes of MN-heterozygous subjects, distinguishing the NN and N phi mutant variants. A significant increase in the NN GPA variant cell frequency (Vf) was found in benzene-exposed workers as compared with unexposed control individuals (mean +/- SEM, 13.9 +/- 1.7 per million cells vs. 7.4 +/- 1.1 per million cells in control individuals; P = 0.0002). In contrast, no significant difference existed between the two groups for the N phi Vf (9.1 +/- 0.9 vs. 8.8 +/- 1.8 per million cells; P = 0.21). Further, lifetime cumulative occupational exposure to benzene was associated with the NN Vf (P = 0.005) but not with the N phi Vf (P = 0.31), suggesting that NN mutations occur in longer-lived bone marrow stem cells. NN variants result from loss of the GPA M allele and duplication of the N allele, presumably through recombination mechanisms, whereas NO variants arise from gene inactivation, presumably due to point mutations and deletions. Thus, these results suggest that benzene produces gene-duplicating mutations but does not produce gene-inactivating mutations at the GPA locus in bone marrow cells of humans exposed to high benzene levels. This finding is consistent with data on the genetic toxicology of benzene and its metabolites and adds further weight to the hypothesis that chromosome damage and mitotic recombination are important in benzene-induced leukemia.

Neoplasia in childhood--25 years of progress

BACKGROUND

Several factors have contributed to the improved prognosis for the survival and quality of life of children with cancer. Childhood tumours tend to have their origin in intrinsic genetic abnormalities, and are usually disseminated by the time of diagnosis. As a result, conventional treatments, such as ablative surgery and/or radiotherapy (the effects of which are detrimental to the growth and development of normal tissues), are rarely successful. The advent of effective combination chemotherapy, given as an adjuvant to eradicate micrometastases, has led also to the dramatic regression of inoperable primary tumours. Subsequent surgery often enables complete resection without the need for radiotherapy. Primary surgery is now used to obtain sufficient tissue to make a precise diagnosis, and recently developed molecular techniques make this possible with great precision from needle biopsies in many instances. The development of an effective treatment regimen is the single most important prognostic factor. This also permits analysis of the differences between successfully treated groups and those not cured by standard treatment. These prognostic factors usually have a biological basis that is identifiable at diagnosis, allowing stratification of treatments and further development. Some of the worst prognosis cases on past standard therapy, such as B-cell acute lymphoblastic leukaemia, have an excellent prognosis when specific treatment regimens are designed to fit their particular characteristics. The finding of specific genetic mutations underlying many childhood tumours may now provide an 'Achilles heel' to enable the development of highly specific therapies that are relatively non-toxic to the normal tissues undergoing rapid growth and development during childhood. The rarity of childhood cancer and the need for multidisciplinary management make it impossible for the ordinary district hospital to deliver optimal treatment, though 'maintenance' treatment and follow-up can be delivered locally as part of 'shared care' with a regional centre. These centres are members of the U.K. Children's Cancer Study Group which was formed in 1977 and now treats 75%. of all cases of childhood malignancy, with sufficient numbers to run randomized clinical trials for most tumour types, often in collaboration with other national paediatric oncology groups in Europe and the U.S.A.

CONCLUSION

Children with cancer are likely to be major beneficiaries from the recent advances in the understanding of neoplasia, many of which stem from work on paediatric malignancies. It is therefore important and mutually advantageous to foster and maintain close links with mainstream 'adult' oncology and with the cancer research institutions.