Sequence analysis of the ATM gene in 20 patients with RTOG grade 3 or 4 acute and/or late tissue radiation side effects

A Novel Alu Element Insertion in ATM Induces Exon Skipping in Suspected HBOC Patients

The vast majority of patients at risk of hereditary breast and/or ovarian cancer (HBOC) syndrome remain without a molecular diagnosis after routine genetic testing. One type of genomic alteration that is commonly missed by diagnostic pipelines is mobile element insertions (MEIs). Here, we reanalyzed multigene panel data from suspected HBOC patients using the MEI detection tool Mobster. A novel Alu element insertion in ATM intron 54 (ATM:c.8010+30_8010+31insAluYa5) was identified as a potential contributing factor in seven patients. Transcript analysis of patient-derived RNA from three heterozygous carriers revealed exon 54 skipping in 38% of total ATM transcripts. To manifest the direct association between the Alu element insertion and the aberrant splice pattern, HEK293T and MCF7 cells were transfected with wild-type or Alu element-carrying minigene constructs. On average, 77% of plasmid-derived transcripts lacked exon 54 in the presence of the Alu element insertion compared to only 4.7% of transcripts expressed by the wild-type minigene. These results strongly suggest ATM:c.8010+30_8010+31insAluYa5 as the main driver of ATM exon 54 skipping. Since this exon loss is predicted to cause a frameshift and a premature stop codon, mutant transcripts are unlikely to translate into functional proteins. Based on its estimated frequency of up to 0.05% in control populations, we propose to consider ATM:c.8010+30_8010+31insAluYa5 in suspected HBOC patients and to clarify its role in carcinogenesis through future epidemiological and functional analyses. Generally, the implementation of MEI detection tools in diagnostic sequencing pipelines could increase the diagnostic yield, as MEIs are likely underestimated contributors to genetic diseases.

Double Heterozygous Mutations in the BRCA2 and ATM Genes: A Case Report and Review of the Literature

Introduction

Germline mutations of the BRCA1 and BRCA2 genes are responsible for about a quarter of hereditary breast cancers (BCs). In this study, we aimed to determine the importance of rare double heterozygous (DH) pathogenic variant carriership in BRCA2and ATM genes in a patient diagnosed with BC and pancreas cancer (PC).

Case Report

A 54-year-old female patient was diagnosed with BC at the age of 34 years and with PC at the age of 48 years. The multigene panel and next-generation sequencing technique were used to evaluate the status of the patient's cancer susceptibility genes. Pathogenic variants c.537dup (p.Ile180Tyrfs*3) in the BRCA2 gene and c.5065C>T (p.Gln1689Ter) in the ATM gene were detected as DH in the patient. Co-segregation analysis was performed on the relatives of the patient using Sanger sequencing.

Discussion/Conclusion

Multiple primary malignant neoplasms can be encountered more frequently in DH pathogenic variant carriers, and the diagnosis of malignancies can be made at an earlier age through surveillance guided by genetic testing. In this rare case, more patient studies are needed to determine the contribution of DH in BRCA2 and ATM genes to the phenotype.

Is Clinical Radiosensitivity a Complex Genetically Controlled Event?

New insights into molecular mechanisms responsible for cellular radiation response are coming from recent basic radiobiological studies. Preliminary data supporting the concept of clinical radiosensitivity as a complex genetically controlled event are available, and it seems reasonable to hypothesize that genes encoding for proteins implicated in known radiation-induced pathways, such as DNA repair, could influence normal tissue and tumor response to radiotherapy. Such genes could be considered as candidates for experimental studies and as targets for innovative therapies. Variants that could influence individual radiosensitivity have been recently identified, and specific Single Nucleotide Polymorphisms have been associated to the development of different radiation effects on normal tissues. Allelic architecture of complex traits able to modify phenotypes is difficult to be established, and different grades of interaction between common or rare genetic determinants may be present and should be considered. Many different experimental strategies could be investigated in the future, such as analysis of multiple genes in large irradiated patient cohorts strictly observed for radiation effects or identification of new candidate genes, with the aim of identifying factors that could be employed in predictive testing and individualization of radiation therapy on a genetic basis.

Ataxia-telangiectasia gene (ATM) mutation heterozygosity in breast cancer: a narrative review

Background

Despite the fact that heterozygosity for a pathogenic ATM variant is present in 1%-2% of the adult population, clinical guidelines to inform physicians and genetic counsellors about optimal management in that population are lacking.

Methods

In this narrative review, we describe the challenges and controversies in the management of women who are heterozygous for a pathogenic ATM variant with respect to screening for breast and other malignancies, to choices for systemic therapy, and to decisions about radiation therapy.

Results

Given that the lifetime risk for breast cancer in women who are heterozygous for a pathogenic ATM variant is likely greater than 25%, those women should undergo annual mammographic screening starting at least by 40 years of age. For women in this group who have a strong family history of breast cancer, earlier screening with both magnetic resonance imaging and mammography should be considered. High-quality data to inform the management of established breast cancer in carriers of pathogenic ATM variants are lacking. Although deficiency in the ATM gene product might confer sensitivity to dna-damaging pharmaceuticals such as inhibitors of poly (adp-ribose) polymerase or platinum agents, prospective clinical trials have not been conducted in the relevant patient population. Furthermore, the evidence with respect to radiation therapy is mixed; some data suggest increased toxicity, and other data suggest improved clinical benefit from radiation in women who are carriers of a pathogenic ATM variant.

Conclusions

As in the 2017 U.S. National Comprehensive Cancer Network guidelines, we recommend high-risk imaging for women in Ontario who are heterozygous for a pathogenic ATM variant. Currently, ATM carrier status should not influence decisions about systemic or radiation therapy in the setting of an established breast cancer diagnosis.

ATM Mutations in Cancer: Therapeutic Implications

Activation of checkpoint arrest and homologous DNA repair are necessary for maintenance of genomic integrity during DNA replication. Germ-line mutations of the ataxia telangiectasia mutated (ATM) gene result in the well-characterized ataxia telangiectasia syndrome, which manifests with an increased cancer predisposition, including a 20% to 30% lifetime risk of lymphoid, gastric, breast, central nervous system, skin, and other cancers. Somatic ATM mutations or deletions are commonly found in lymphoid malignancies, as well as a variety of solid tumors. Such mutations may result in chemotherapy resistance and adverse prognosis, but may also be exploited by existing or emerging targeted therapies that produce synthetic lethal states. Mol Cancer Ther; 15(8); 1781-91. ©2016 AACR.

Assessment of Radiation Induced Therapeutic Effect and Cytotoxicity in Cancer Patients Based on Transcriptomic Profiling

Toxicity induced by radiation therapy is a curse for cancer patients undergoing treatment. It is imperative to understand and define an ideal condition where the positive effects notably outweigh the negative. We used a microarray meta-analysis approach to measure global gene-expression before and after radiation exposure. Bioinformatic tools were used for pathways, network, gene ontology and toxicity related studies. We found 429 differentially expressed genes at fold change >2 and p-value <0.05. The most significantly upregulated genes were synuclein alpha (SNCA), carbonic anhydrase I (CA1), X-linked Kx blood group (XK), glycophorin A and B (GYPA and GYPB), and hemogen (HEMGN), while downregulated ones were membrane-spanning 4-domains, subfamily A member 1 (MS4A1), immunoglobulin heavy constant mu (IGHM), chemokine (C-C motif) receptor 7 (CCR7), BTB and CNC homology 1 transcription factor 2 (BACH2), and B-cell CLL/lymphoma 11B (BCL11B). Pathway analysis revealed calcium-induced T lymphocyte apoptosis and the role of nuclear factor of activated T-cells (NFAT) in regulation of the immune response as the most inhibited pathways, while apoptosis signaling was significantly activated. Most of the normal biofunctions were significantly decreased while cell death and survival process were activated. Gene ontology enrichment analysis revealed the immune system process as the most overrepresented group under the biological process category. Toxicity function analysis identified liver, kidney and heart to be the most affected organs during and after radiation therapy. The identified biomarkers and alterations in molecular pathways induced by radiation therapy should be further investigated to reduce the cytotoxicity and development of fatigue.

Rare, evolutionarily unlikely missense substitutions in ATM confer increased risk of breast cancer

The susceptibility gene for ataxia telangiectasia, ATM, is also an intermediate-risk breast-cancer-susceptibility gene. However, the spectrum and frequency distribution of ATM mutations that confer increased risk of breast cancer have been controversial. To assess the contribution of rare variants in this gene to risk of breast cancer, we pooled data from seven published ATM case-control mutation-screening studies, including a total of 1544 breast cancer cases and 1224 controls, with data from our own mutation screening of an additional 987 breast cancer cases and 1021 controls. Using an in silico missense-substitution analysis that provides a ranking of missense substitutions from evolutionarily most likely to least likely, we carried out analyses of protein-truncating variants, splice-junction variants, and rare missense variants. We found marginal evidence that the combination of ATM protein-truncating and splice-junction variants contribute to breast cancer risk. There was stronger evidence that a subset of rare, evolutionarily unlikely missense substitutions confer increased risk. On the basis of subset analyses, we hypothesize that rare missense substitutions falling in and around the FAT, kinase, and FATC domains of the protein may be disproportionately responsible for that risk and that a subset of these may confer higher risk than do protein-truncating variants. We conclude that a comparison between the graded distributions of missense substitutions in cases versus controls can complement analyses of truncating variants and help identify susceptibility genes and that this approach will aid interpretation of the data emerging from new sequencing technologies.

Genetic variants and normal tissue toxicity after radiotherapy: a systematic review

During the last decade, nearly 60 studies have addressed possible associations between various genetic sequence alterations and risk of adverse reactions after radiotherapy. We report here an overview of these studies with information on the genetic variants, tumour type, number of patients included, the endpoint studied, the mechanism(s) by which the candidate genes are involved in the pathogenesis of normal tissue toxicity, and odds ratios (ORs) for candidate variants. Though many positive results have been reported, inconsistent findings and non-replication of previous results have frequently occurred. This can presumably be attributed to certain methodological shortcomings including lack of statistical power to detect small effect sizes. Based on theoretical considerations and experiences from other scientific fields, we discuss how future studies should be designed in order to successfully unravel the genetics of normal tissue radiosensitivity. We propose a model of the allelic architecture that may underlie differences in normal tissue radiosensitivity. Genome wide association studies have proven a powerful tool to identify novel loci that affect various phenotypes. Nonetheless, genome wide association studies are extremely demanding in terms of sample size. Furthermore, certain limitations still relate to this kind of studies, emphasizing the need for international consortia such as the ESTRO GENEPI.

Genetic variations in DNA repair genes, radiosensitivity to cancer and susceptibility to acute tissue reactions in radiotherapy-treated cancer patients

Ionizing radiation is a well established carcinogen for human cells. At low doses, radiation exposure mainly results in generation of double strand breaks (DSBs). Radiation-related DSBs could be directly linked to the formation of chromosomal rearrangements as has been proven for radiation-induced thyroid tumors. Repair of DSBs presumably involves two main pathways, non-homologous end joining (NHEJ) and homologous recombination (HR). A number of known inherited syndromes, such as ataxia telangiectasia, ataxia-telangiectasia like-disorder, radiosensitive severe combined immunodeficiency, Nijmegen breakage syndrome, and LIG4 deficiency are associated with increased radiosensitivity and/or cancer risk. Many of them are caused by mutations in DNA repair genes. Recent studies also suggest that variations in the DNA repair capacity in the general population may influence cancer susceptibility. In this paper, we summarize the current status of DNA repair proteins as potential targets for radiation-induced cancer risk. We will focus on genetic alterations in genes involved in HR- and NHEJ-mediated repair of DSBs, which could influence predisposition to radiation-related cancer and thereby explain interindividual differences in radiosensitivity or radioresistance in a general population.

Genetic markers for prediction of normal tissue toxicity after radiotherapy

During the last decade, a number of studies have supported the hypothesis that there is an important genetic component to the observed interpatient variability in normal tissue toxicity after radiotherapy. This review summarizes the candidate gene association studies published so far on the risk of radiation-induced morbidity and highlights some recent successful whole-genome association studies showing feasibility in other research areas. Future genetic association studies are discussed in relation to methodological problems such as the characterization of clinical and biological phenotypes, genetic haplotypes, and handling of confounding factors. Finally, candidate gene studies elucidating the genetic component of radiation-induced morbidity and the functional consequences of single nucleotide polymorphisms by studying intermediate phenotypes will be discussed.

Predicting Risk of Radiation-Induced Lung Injury

Radiation-induced lung injury (RILI) is the most common, dose-limiting complication of thoracic radio- and radiochemotherapy. Unfortunately, predicting which patients will suffer from this complication is extremely difficult. Ideally, individual phenotype- and genotype-based risk profiles should be able to identify patients who are resistant to RILI and who could benefit from dose escalation in chemoradiotherapy. This could result in better local control and overall survival. We review the risk predictors that are currently in clinical use--dosimetric parameters of radiotherapy such as normal tissue complication probability, mean lung dose, V20 and V30--as well as biomarkers that might individualize risk profiles. These biomarkers comprise a variety of proinflammatory and profibrotic cytokines and molecules including transforming growth factor beta1 that are implicated in development and persistence of RILI. Dosimetric parameters of radiotherapy show a low negative predictive value of 60% to 80%. Depending on the studied molecule, negative predictive value of biomarkers is approximately 50%. The predictive power of biomarkers might be increased if they are coupled with radiogenomics, e.g., genotyping analysis of single nucleotide polymorphisms in transforming growth factor beta1, transforming growth factor beta1 pathway genes, and other cytokines. Genetic variability and the complexity of RILI and its underlying molecular mechanisms make identification of biological risk predictors challenging. Further investigations are needed to develop more effective risk predictors of RILI.

The genomics revolution and radiotherapy

The expansion of our knowledge through the Human Genome Project has been accompanied by the development of new high-throughput techniques, which provide extensive capabilities for the analysis of a large number of genes or the whole genome. These assays can be carried out in various clinical samples at the DNA (genome), RNA (transcriptome) or protein (proteome) level. There is a belief that this genomic revolution, i.e. sequencing of the human genome and developments in high-throughput technology, heralds a future of personalised medicine. For clinical oncology, this progress should increase the possibility of predicting individual patient responses to radiotherapy. This review highlights some of the work involving sparsely ionising radiation and the new technologies.

Genetic predictors of adverse radiotherapy effects: the Gene-PARE project

PURPOSE

The development of adverse effects resulting from the radiotherapy of cancer limits the use of this treatment modality. The validation of a test capable of predicting which patients would be most likely to develop adverse responses to radiation treatment, based on the possession of specific genetic variants, would therefore be of value. The purpose of the Genetic Predictors of Adverse Radiotherapy Effects (Gene-PARE) project is to help achieve this goal.

METHODS AND MATERIALS

A continuously expanding biorepository has been created consisting of frozen lymphocytes and DNA isolated from patients treated with radiotherapy. In conjunction with this biorepository, a database is maintained with detailed clinical information pertaining to diagnosis, treatment, and outcome. The DNA samples are screened using denaturing high performance liquid chromatography (DHPLC) and the Surveyor nuclease assay for variants in ATM, TGFB1, XRCC1, XRCC3, SOD2, and hHR21. It is anticipated that additional genes that control the biologic response to radiation will be screened in future work.

RESULTS

Evidence has been obtained that possession of variants in genes, the products of which play a role in radiation response, is predictive for the development of adverse effects after radiotherapy.

CONCLUSIONS

It is anticipated that the Gene-PARE project will yield information that will allow radiation oncologists to use genetic data to optimize treatment on an individual basis.

Can risk of radiotherapy-induced normal tissue complications be predicted from genetic profiles?

Over the last decade, increasing efforts have been taken to establish associations between various genetic germline alterations and risk of normal tissue complications after radiotherapy. Though the studies have been relatively small and methodologically heterogeneous, preliminary indications have been provided that single nucleotide polymorphisms in the genes TGFB1 and ATM may modulate risk of particularly late toxicity. In addition, rare ATM alterations may enhance complication susceptibility. Nevertheless, we are still far from having an exhaustive understanding of the genetics that may underlie differences in clinical normal tissue radiosensitivity. Recent technical advances and emerging insights to the structure of inter-individual genetic variation open up unprecedented opportunities to dissect the molecular and genetic basis of normal tissue radiosensitivity. However, to fully exploit these new possibilities well-planed large-scale clinical studies are mandatory. Currently, international initiatives are taken to establish the bio banks and databases needed for this task.

Microsatellite polymorphisms in DNA repair genes XRCC1, XRCC3 and XRCC5 in patients with gynecological tumors: association with late clinical radiosensitivity and cancer incidence

This study investigates the association of microsatellite polymorphisms in XRCC1, XRCC3 and XRCC5 with the development of late radiation-induced radiotherapy reactions and examines the correlation between these microsatellites and cancer incidence. Sixty-two women with cervical or endometrial cancer treated with radiotherapy were included in the study. According to the CTCAEv3.0 scale, 22 patients showed late adverse radiotherapy reactions (grade 2 or more). PCR on lymphocyte DNA followed by automated fragment analysis was performed to examine the number of tandem repeat units at each locus. No significant association was found between the repeat length at any of the microsatellites in XRCC1, XRCC3 or XRCC5 and the incidence of late radiotherapy complications. Since higher odds ratios (ORs) were found for the rare XRCC1 [AC]11 and [AC]21 repeats (OR = 2.65, P = 0.325 and OR = 8.67, P = 0.093, respectively), the possible involvement of these small and large repeats in clinical radiosensitivity cannot be completely ruled out. When specific numbers of repeats were examined, no significant correlation was found between the microsatellite repeat length in XRCC1 and XRCC5 and cancer incidence. A weak correlation between XRCC3 [AC]16 homozygotes and cancer incidence was found (OR = 2.56, P = 0.055). A large-scale multicenter study of cancer patients with a high number of radiosensitive individuals is needed to clarify the value of rare polymorphic microsatellite repeats in XRCC1 and XRCC3 as a biomarker of clinical radiosensitivity or increased cancer risk.

Normal expression of DNA repair proteins, hMre11, Rad50 and Rad51 but protracted formation of Rad50 containing foci in X-irradiated skin fibroblasts from radiosensitive cancer patients

About 5% of oncology patients treated by radiation therapy develop acute or late radiotoxic effects whose molecular mechanisms remain poorly understood. In this study, we evaluated the potential role of DNA repair proteins in the hypersensitivity of cancer patients to radiation therapy. The expression levels and focal nuclear distribution of DNA repair proteins, hMre11, Rad50 and Rad51 were investigated in skin fibroblasts strains derived from cancer patients with adverse early skin reaction to radiotherapy using Western blot and foci immunofluorescence techniques, respectively. Cells from cancer patients with normal reaction to radiotherapy as well as cells from apparently healthy subjects served as controls. Cellular radiosensitivity after in vitro irradiation was assessed by the clonogenic survival assay. The clonogenic survival assay and Western blot analysis of the DNA repair proteins did not reveal any abnormalities in cellular radiosensitivity in vitro and in protein expression levels or their migration patterns in the fibroblasts derived from cancer patients with hypersensitive reaction to radiotherapy. In contrast, in vitro irradiated cells from radiosensitive patients exhibited a significantly higher number of nuclei with focally concentrated Rad50 protein than in both control groups. The observed alteration of the distribution of radiation-induced Rad50 foci in cells derived from cancer patients with acute side reactions to radiotherapy might contribute to their radiation therapy outcome. These data suggest the usefulness of the Rad50 foci analysis for predicting clinical response of cancer patients to radiotherapy.

Pharmacogenomics and breast cancer

Germline variants can be used to study breast cancer susceptibility as well as the variable response to both drug and radiation therapy used in the treatment of breast cancer. In addition to germline high-penetrance mutations important in familial and hereditary breast cancer, a substantial component of breast cancer risk can be attributed to the combined effect of many low-risk germline polymorphisms involved in relevant pathways like those of DNA repair, adhesion, carcinogen and estrogen metabolism. Additionally, the identification of sequence variants in genes involved in response to chemotherapy and radiation treatment, has created the opportunity to apply genomics to individualized treatment. The continued insight into the molecular pathways involved in drug and radiation response has enabled progress in tailoring therapies in such a way as to both maximize efficacy and minimize toxicity. Polymorphisms in genes encoding drug-metabolizing enzymes, drug transporters and drug targets can be used to predict toxicity and response to pharmacologic agents used in breast cancer treatment. Similarly, germline variants in genes involved in DNA repair, radiation-induced fibrosis and reactive oxygen species may be used to predict response to radiation therapy. As a result, pharmacogenomics is rapidly evolving to affect the entire spectrum of breast cancer management, influencing both prevention and treatment choices.

Toxicity from radiation therapy associated with abnormal transcriptional responses to DNA damage

Toxicity from radiation therapy is a grave problem for cancer patients. We hypothesized that some cases of toxicity are associated with abnormal transcriptional responses to radiation. We used microarrays to measure responses to ionizing and UV radiation in lymphoblastoid cells derived from 14 patients with acute radiation toxicity. The analysis used heterogeneity-associated transformation of the data to account for a clinical outcome arising from more than one underlying cause. To compute the risk of toxicity for each patient, we applied nearest shrunken centroids, a method that identifies and cross-validates predictive genes. Transcriptional responses in 24 genes predicted radiation toxicity in 9 of 14 patients with no false positives among 43 controls (P = 2.2 x 10(-7)). The responses of these nine patients displayed significant heterogeneity. Of the five patients with toxicity and normal responses, two were treated with protocols that proved to be highly toxic. These results may enable physicians to predict toxicity and tailor treatment for individual patients.

Radiation-hypersensitive cancer patients do not manifest protein expression abnormalities in components of the nonhomologous end-joining (NHEJ) pathway

Radiation therapy (RT) is utilised for the treatment of around half of all oncology patients during the course of their illness. Despite great clinical progress in the rational deployment of RT, the underlying molecular basis for its efficacy and toxicity are currently imperfectly understood. In this study, we took a biochemical approach to evaluate the potential role of key ionising radiation repair proteins in the treatment outcomes of patients with severe acute or late RT side effects. Lymphoblastoid cell lines were established from blood samples from 36 radiosensitive cases and a number of controls (the latter had had RT but did not develop significant toxicity). The expression level and migration of key proteins from the nonhomologous end-joining (NHEJ) pathway was evaluated by Western blot analysis on cases and controls. We did not observe any abnormalities in expression level or migration pattern of the following NHEJ proteins in radiosensitive cancer cases: Ku70, Ku80, XRCC4, DNA Ligase IV. These important negative results provide evidence that mutations that affect protein expression of these NHEJ components are unlikely to underlie clinical radiation sensitivity.

Molecular and genetic markers in the local-regional management of breast cancer

The clinical application of molecular markers in the diagnosis, staging, and management of breast cancer continues to expand. Although the use of molecular markers in local-regional disease does not approach the level of their application in the systemic management of breast cancer, a growing body of rature supports the potential for molecular and genetic factors in clinical decision making regarding the local-regional management of breast cancer. As with conventional clinical and histopathologic factors, data regarding molecular and genetic factors as they relate to local-regional relapse may be conflicting and are subject to the usual limitations of predominantly retrospective studies. There are, however, some consistent data suggesting associations between local-regional control of disease and several molecular markers, including hormone receptor status, HER2/neu, p53, proliferative markers, and others. Interpretation of these data and how to use this information in clinical practice remains challenging. The available rature regarding the use of genetic and molecular markers in the local-regional management of breast cancer is summarized in this review.

Does variability in normal tissue reactions after radiotherapy have a genetic basis – where and how to look for it?

Cancer patients exhibit large patient-to-patient variability in normal tissue reactions after radiotherapy. Several observations support the hypothesis that clinical normal tissue radiosensitivity is influenced by genetic factors. However, very little is known about the genetic variation possibly underlying inter-individual differences in normal tissue reactions when unselected cancer patients undergo radiotherapy. It seems reasonable to assume that clinical radiosensitivity of normal tissues should be regarded as a so-called complex trait depending on the combined effect of several different genetic alterations. Single nucleotide polymorphisms (SNPs) make up 90% of naturally occurring sequence variation in the human genome and SNPs in genes related to the biological response to ionising radiation may affect clinical radiosensitivity. Rare genetic variants could also possibly play an important role. Thus, the 'allelic architecture' underlying differences in normal tissue reactions may be rather complicated. Recent advances in high throughput genotyping and bio-informatics provide unprecedented opportunities to unravel the genetic basis of clinical normal tissue radiosensitivity. However, to achieve maximum benefit from these advances, carefully designed clinical studies with an accrual of hundreds or thousands of patients are probably needed.

ATM mutations in female breast cancer patients predict for an increase in radiation-induced late effects

PURPOSE

Mutation of the ATM gene may be associated with enhanced radiosensitivity and increased radiation-induced morbidity. Denaturing high performance liquid chromatography (DHPLC) is a powerful new technique proven to be sensitive and accurate in the detection of missense mutations, as well as small deletions and insertions. We screened female breast cancer patients for evidence of ATM gene alterations using DHPLC. This study attempted to determine whether breast cancer patients who develop severe radiotherapy (RT)-induced effects are more likely to possess ATM mutations than patients who display normal radiation responses.

METHODS AND MATERIALS

Forty-six patients with early-stage breast carcinoma underwent limited surgery and adjuvant RT. DNA was isolated from blood lymphocytes, and each coding exon of the ATM gene was amplified using polymerase chain reaction. Genetic variants were identified using DHPLC by comparing test patterns with a known wild-type pattern. All variants were subjected to DNA sequencing and compared with wild-type sequences for evidence of a mutation. A retrospective review was performed, and the Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer acute and late morbidity scoring schemes for skin and subcutaneous normal tissues were applied to quantify the radiation-induced effects.

RESULTS

Nine ATM mutations were identified in 6 patients (8 novel and 1 rare). The median follow-up was 3.2 years (range 1.3-10.3). A significant correlation between ATM mutation status and the development of Grade 3-4 subcutaneous late effects was found. All 3 of the patients (100%) who manifested Grade 3-4 subcutaneous late sequelae possessed ATM mutations, whereas only 3 (7%) of the 43 patients who did not develop this form of severe toxicity harbored an ATM mutation (p = 0.001). One ATM mutation carrier developed Grade 4 soft tissue necrosis after RT and required hyperbaric oxygen. All 3 patients manifesting Grade 3-4 late subcutaneous responses in fact harbored 2 ATM mutations. In contrast, none of the 3 ATM carriers who had a single mutation developed a severe subcutaneous reaction. ATM mutation status did not predict for a significant increase in early effects. Of the 23 patients with Grade 2-3 moist desquamation, 4 (17%) had an ATM mutation compared with 2 (9%) of 23 patients without desquamation (p = 0.7).

CONCLUSION

Possession of an ATM mutation, particularly when 2 are present, may be predictive of an increase in subcutaneous late tissue effects after RT for breast cancer and may subsequently prove to be a relative contraindication to standard management. These patients may be better served with reduced doses of radiation. Equivalent local control remains to be tested, but this germline alteration may radiosensitize normal tissues, as well as the tumor itself. DHPLC is effective in the identification of these patients. A larger study is required to confirm these findings.

Genomic instability: potential contributions to tumour and normal tissue response, and second tumours, after radiotherapy

PURPOSE

Induced genomic instability generally refers to a type of damage which is transmissible down cell generations, and which results in a persistently enhanced frequency of de novo mutations, chromosomal abnormalities or lethality in a significant fraction of the descendant cell population. The potential contribution of induced genomic instability to tumour and normal tissue response, and second tumours, after radiotherapy, is explored.

RESULTS

The phenomenon of spontaneous genomic instability is well known in some rare genetic diseases (e.g. Gorlin's syndrome), and there is evidence in such cases that it can lead to a greater propensity for carcinogenesis (with shortened latency) which is enhanced after irradiation. It is unclear what role induced genomic instability plays in the response of normal individuals, but persistent chromosomal instability has been detected in vivo in lymphocytes and keratinocytes from irradiated normal individuals. Such induced genomic instability might play some role in tumour response in a subset of tumours with specific defects in damage response genes, but again its contribution to radiocurability in the majority of cancer patients is unclear. In normal tissues, genomic instability induced in wild-type cells leading to delayed cell death might contribute to more severe or prolonged early reactions as a consequence of increased cell loss, a longer time required for recovery, and greater residual injury. In tumours, induced genomic instability reflected in delayed reductions in clonogenic capacity might contribute to the radiosensitivity of primary tumours, and also to a lower incidence, longer latency and slower growth rate of recurrences and metastases.

CONCLUSIONS

The evidence which is reviewed shows that there is little information at present to support these propositions, but what exists is consistent with their expectations. Also, it is not yet clear to what extent mutations associated with genomic instability, particularly gene polymorphisms, or other low penetrant gene mutations, contribute to the recognized spectrum of normal tissue radiosensitivity amongst cancer patients, or in the general population. Tests for such genetic modifications may help in the search for more accurate prognostic markers of response, which hopefully could be used in addition to other strategies to further improve the outcome for cancer patients given radiotherapy.

Screening breast cancer patients for Norwegian ATM mutations

483 Norwegian breast cancer patients were screened for six different ataxia telangiectasia mutated (ATM) mutations previously found to account for 83% of the disease alleles in Norwegian ataxia telangiectasia (AT) patients. Only one carrier was found. These results provide no evidence in favour of an excess risk of breast cancer associated with heterozygosity for classical AT mutations, but remain consistent with a maximum 2.4-fold increased risk.

Mutation analysis of BRCA1 and BRCA2 cancer predisposition genes in radiation hypersensitive cancer patients

PURPOSE

The dose intensity of radiotherapy (RT) used in cancer treatment is limited in rare individuals who display severe normal tissue reactions after standard RT treatments. Novel predictive assays are required to identify these individuals prior to treatment. The mechanisms responsible for such reactions are unknown, but may involve dysfunction of genes involved in the sensing and response of cells to DNA damage. The breast cancer susceptibility genes BRCA1 and BRCA2 are implicated in DNA damage repair and the control of genome stability. The purpose of this study was to determine if clinical radiation hypersensitivity is related to mutations of the BRCA1 and BRCA2 genes. Such information is of potential use in the clinical management of BRCA mutation carriers and their families.

METHODS AND MATERIALS

Twenty-two cancer patients who developed severe normal tissue reactions after RT were screened for mutations of BRCA1 and BRCA2, using various methods including protein truncation testing, direct DNA sequencing, and a PCR-based BRCA1 exon 13 duplication test.

RESULTS

No mutations were detected in the 22 patients tested, despite screening for the majority of commonly described types of mutations of BRCA1 and BRCA2.

CONCLUSION

These early results suggest that genes other than BRCA1 and BRCA2 probably account for most cases of clinical radiation hypersensitivity, and that screening for mutations of BRCA1 and BRCA2 is unlikely to be useful in predicting response to radiotherapy. However, it has not been excluded that some BRCA1 or BRCA2 heterozygotes might experience unexpected RT toxicity; further BRCA mutation screening on radiation sensitive individuals is warranted.

The ATM gene and breast cancer: is it really a risk factor?

The genetic determinants for most breast cancer cases remain elusive. Whilst mutations in BRCA1 and BRCA2 significantly contribute to familial breast cancer risk, their contribution to sporadic breast cancer is low. In such cases genes frequently altered in the general population, such as the gene mutated in Ataxia telangiectasia (AT), ATM may be important risk factors. The initial interest in studying ATM heterozygosity in breast cancer arose from the findings of epidemiological studies of AT families in which AT heterozygote women had an increased risk of breast cancer and estimations that 1% of the population are AT heterozygotes. One of the clinical features of AT patients is extreme cellular sensitivity to ionising radiation. This observation, together with the finding that a significant proportion of breast cancer patients show an exaggerated acute or late normal tissue reactions after radiotherapy, has lead to the suggestion that AT heterozygosity plays a role in radiosensitivity and breast cancer development. Loss of heterozygosity in the region of the ATM gene on chromosome 11, has been found in about 40% of sporadic breast tumours. However, screening for ATM mutations in sporadic breast cancer cases, showing or not adverse effects to radiotherapy, has not revealed the magnitude of involvement of the ATM gene expected. Their size and the use of the protein truncation test to identify mutations limit many of these studies. This latter parameter is critical as the profile of mutations in AT patients may not be representative of the ATM mutations in other diseases. The potential role of rare sequence variants within the ATM gene, sometimes reported as polymorphisms, also needs to be fully assessed in larger cohorts of breast cancer patients and controls in order to determine whether they represent cancer and/or radiation sensitivity predisposing mutations.

Radiation-recall skin disorders associated with the use of antineoplastic drugs. Pathogenesis, prevalence, and management

Radiation-recall dermatitis is the occurrence, with subsequent administration of cytotoxic chemotherapy, of an acute inflammatory toxicity in a previously quiescent radiation field. It may occur from days to weeks, and sometimes years, after the radiation therapy. The precise mechanism is unknown. One hypothesis suggests that the initial radiation therapy leads to a depletion of tissue stem cells within the irradiated field and that subsequent cytotoxic chemotherapy exposure causes a 'remembered' reaction among the remaining surviving cells. An alternative proposition suggests that radiation induces heritable mutations within surviving cells, which then produce a subgroup of defective stem cells that are unable to tolerate the second insult of chemotherapy. Recently, ataxia telangiectasia gene mutation and protein kinase deficiency have been associated with patients who have increased susceptibility to severe radiation-induced skin toxicity. Most of the lesions will heal with supportive treatment. Although some reports have noted that radiation-recall dermatitis recurred with subsequent continued administration of the same chemotherapeutic agent, such experience is not universal. At present, a decision as to whether the same chemotherapeutic agent can be continued will usually be determined by the severity of the initial reaction, the chemoresponsiveness of the tumor to this particular agent, the individual patient's wishes, and a clinical judgment that takes into account the availability of alternative therapy.