Mutational signatures of ionizing radiation in second malignancies

Mutation Profiling of Key Cancer Genes in Primary Breast Cancers and Their Distant Metastases

Although the repertoire of somatic genetic alterations of primary breast cancers has been extensively catalogued, the genetic differences between primary and metastatic tumors have been less studied. In this study, we compared somatic mutations and gene copy number alterations of primary breast cancers and their matched metastases from patients with estrogen receptor (ER)-negative disease. DNA samples obtained from formalin-fixed paraffin-embedded ER-negative/HER2-positive (n = 9) and ER-, progesterone receptor (PR-), HER2-negative (n = 8) primary breast cancers and from paired brain or skin metastases and normal tissue were subjected to a hybridization capture-based massively parallel sequencing assay, targeting 341 key cancer genes. A large subset of nonsynonymous somatic mutations (45%) and gene copy number alterations (55%) was shared between the primary tumors and paired metastases. However, mutations restricted to either a given primary tumor or its metastasis, the acquisition of loss of heterozygosity of the wild-type allele, and clonal shifts of genes affected by somatic mutations, such as TP53 and RB1, were observed in the progression from primary tumors to metastases. No metastasis location-specific alterations were identified, but synchronous metastases showed higher concordance with the paired primary tumor than metachronous metastases. Novel potentially targetable alterations were found in the metastases relative to their matched primary tumors. These data indicate that repertoires of somatic genetic alterations in ER-negative metastatic breast cancers may differ from those of their primary tumors, even by the presence of driver and targetable somatic genetic alterations.Significance: Somatic genetic alterations in ER-negative breast cancer metastases may be distinct from those of their primary tumors, suggesting that for treatment-decision making, genetic analyses of DNA obtained from the metastatic lesion rather than from the primary tumor should be considered. Cancer Res; 78(12); 3112-21. ©2018 AACR.

Genomic analysis reveals secondary glioblastoma after radiotherapy in a subset of recurrent medulloblastomas

Despite great advances in understanding of molecular pathogenesis and achievement of a high cure rate in medulloblastoma, recurrent medulloblastomas are still dismal. Additionally, misidentification of secondary malignancies due to histological ambiguity leads to misdiagnosis and eventually to inappropriate treatment. Nevertheless, the genomic characteristics of recurrent medulloblastomas are poorly understood, largely due to a lack of matched primary and recurrent tumor tissues. We performed a genomic analysis of recurrent tumors from 17 pediatric medulloblastoma patients. Whole transcriptome sequencing revealed that a subset of recurrent tumors initially diagnosed as locally recurrent medulloblastomas are secondary glioblastomas after radiotherapy, showing high similarity to the non-G-CIMP proneural subtype of glioblastoma. Further analysis, including whole exome sequencing, revealed missense mutations or complex gene fusion events in PDGFRA with augmented expression in the secondary glioblastomas after radiotherapy, implicating PDGFRA as a putative driver in the development of secondary glioblastomas after treatment exposure. This result provides insight into the possible application of PDGFRA-targeted therapy in these second malignancies. Furthermore, genomic alterations of TP53 including 17p loss or germline/somatic mutations were also found in most of the secondary glioblastomas after radiotherapy, indicating a crucial role of TP53 alteration in the process. On the other hand, analysis of recurrent medulloblastomas revealed that the most prevalent alterations are the loss of 17p region including TP53 and gain of 7q region containing EZH2 which already exist in primary tumors. The 7q gain events are frequently accompanied by high expression levels of EZH2 in both primary and recurrent medulloblastomas, which provides a clue to a new therapeutic target to prevent recurrence. Considering the fact that it is often challenging to differentiate between recurrent medulloblastomas and secondary glioblastomas after radiotherapy, our findings have major clinical implications both for correct diagnosis and for potential therapeutic interventions in these devastating diseases.

Applying Precision Oncology Principles in Radiation Oncology

Radiation therapy is a critical component in the curative management of many solid tumor types, and advances in radiation delivery techniques during the past decade have led to improved disease control and quality of life for patients. During the same period, remarkable advances have also been made in understanding the genomic landscape of tumors; however, treatment decisions in radiation oncology continue to depend primarily on clinical and histopathologic characteristics rather than on the genetic features of the tumor or the patient. With the development of novel genomic techniques and their increasing use in clinical practice, radiation oncology is uniquely positioned to leverage these advances to identify novel biomarkers that could inform radiation dose, field, and the use of concurrent systemic agents. Here, we summarize efforts to use genomic techniques to guide radiation decisions, and we highlight some of the current opportunities and challenges that exist in attempting to apply precision oncology principles in radiation oncology.

Radiation quality and intra-chromosomal aberrations: Size matters

The shift from plant to mammalian cell models in radiation cytogenetics hastened the development of methods suitable for the analysis of chromosome-type aberrations. These included methods to detect interchanges that take place between different chromosomes (dicentrics and translocations), and intrachanges occurring within a given chromosome (rings, interstitial deletions and inversions). In this review we consider the relationship between chromosome-type interchanges and intrachanges in response to changes in ionization density (linear energy transfer; LET). In that context, we discuss advantages and disadvantages of more modern methods used to measure intrachanges, and the implications that their increased resolution of measurement may have on the inter-to-intrachange fraction (i.e., the F-ratio). We conclude that the premise of the F-ratio is supported by its biophysical assumptions, but its intended use as an LET-dependent measure of prior radiation exposure is hampered mainly by our inability to accurately assess, on a cell-by-cell basis, inversions and interstitial deletions whose small sizes are below the detection limits of conventional cytogenetic techniques.

Resistance-promoting effects of ependymoma treatment revealed through genomic analysis of multiple recurrences in a single patient

As in other brain tumors, multiple recurrences after complete resection and irradiation of supratentorial ependymoma are common and frequently result in patient death. This standard-of-care treatment was established in the pregenomic era without the ability to evaluate the effect that mutagenic therapies may exert on tumor evolution and in promoting resistance, recurrence, and death. We seized a rare opportunity to characterize treatment effects and the evolution of a single patient's ependymoma across four recurrences after different therapies. A combination of high-depth whole-genome and exome-based DNA sequencing of germline and tumor specimens, RNA sequencing of tumor specimens, and advanced computational analyses were used. Treatment with radiation and chemotherapies resulted in a substantial increase in mutational burden and diversification of the tumor subclonal architecture without eradication of the founding clone. Notable somatic alterations included a MEN1 driver, several epigenetic modifiers, and therapy-induced mutations that impacted multiple other cancer-relevant pathways and altered the neoantigen landscape. These genomic data provided new mechanistic insights into the genesis of ependymoma and pathways of resistance. They also revealed that radiation and chemotherapy were significant forces in shaping the increased subclonal complexity of each tumor recurrence while also failing to eradicate the founding clone. This raises the question of whether standard-of-care treatments have similar consequences in other patients with ependymoma and other types of brain tumors. If so, the perspective obtained by real-time genomic characterization of a tumor may be essential for making effective patient-specific and adaptive clinical decisions.

Clinical and histological features of second breast cancers following radiotherapy for childhood and young adult malignancy

OBJECTIVE

The purpose of this study was to determine the characteristics of early second breast cancer (SBC) among survivors of childhood and young adult malignancy treated with irradiation.

METHODS

We conducted a multicenter retrospective study of women who presented with breast cancer aged 50 years or younger in nine French centers.

RESULTS

121 patients and 141 SBC were analyzed (invasive = 130; non-invasive = 11). The mean age at first cancer diagnosis was 15 years and at initial SBC diagnosis was 38 years. Bilateral disease before the age of 51 years was diagnosed in 16% of the females. The majority of SBC were invasive carcinomas (92%). Among the invasive carcinomas, 39% had a histoprognostic score of III, 3.1% overexpressed HER2 and 29% were triple negative. The proportion of triple negative phenotype SBC was higher in patients older at first cancer diagnosis [RR = 1.2, 95% CI (1.1-1.3)]. 94% of triple negative SBCs developed in breast tissue which had received >20 Gy.

CONCLUSION

We found a high proportion of aggressive SBC following thoracic radiotherapy in childhood or early adulthood. Advances in knowledge: SBC screening is recommended by scientific societies for these child/young-adulthood cancer survivors in the same way as the one for high risk women because of constitutional mutations. Our results support these recommendations, not only because of a similar cumulative risk, but also because of the aggressive histological characteristics.

Ionizing radiation does not impair the mechanisms controlling genetic stability during T cell receptor gene rearrangement in mice

PURPOSE

To determine whether low dose/low dose rate radiation-induced genetic instability may result from radiation-induced inactivation of mechanisms induced by the ATM-dependent DNA damage response checkpoint. To this end, we analysed the faithfulness of T cell receptor (TR) gene rearrangement by V(D)J recombination in DNA from mice exposed to a single dose of X-ray or chronically exposed to low dose rate γ radiation.

MATERIALS AND METHODS

Genomic DNA obtained from the blood or the thymus of wild type or Ogg1-deficient mice exposed to low (0.1) or intermediate/high (0.2-1 Gy) doses of radiation either by acute X-rays exposure or protracted exposure to low dose-rate γ-radiation was used to analyse by PCR the presence of illegitimate TR gene rearrangements.

RESULTS

Radiation exposure does not increase the onset of TR gene trans-rearrangements in irradiated mice. In mice where it happens, trans-rearrangements remain sporadic events in developing T lymphocytes.

CONCLUSION

We concluded that low dose/low dose rate ionizing radiation (IR) exposure does not lead to widespread inactivation of ATM-dependent mechanisms, and therefore that the mechanisms enforcing genetic stability are not impaired by IR in developing lymphocytes and lymphocyte progenitors, including BM-derived hematopoietic stem cells, in low dose/low dose rate exposed mice.

Pathologic Angiogenesis of Malignant Vascular Sarcomas: Implications for Treatment

Angiosarcoma, epithelioid hemangioendothelioma, and Kaposi sarcoma are classified according to the line of differentiation that these neoplastic cells most closely resemble: the endothelial cell. Although these malignant vascular sarcomas demonstrate immunohistochemical and ultrastructural features typical of this lineage, they vary dramatically in presentation and behavior, reflecting oncologic mechanisms unique to each. Antineoplastic therapies offer significant benefit, but because of the rarity of these cancers, novel therapies are slow to develop, and treatment options for these cancers remain limited. Antiangiogenic approaches that have shown benefit in other malignancies have not fully realized their promise in vascular tumors, suggesting that these tumors do not depend entirely on either angiogenic growth factors or on neighboring endothelia that are affected by these agents. Nonetheless, translational studies have begun to unravel these distinct pathologies, identifying novel translocation products, targets of oncogenic virulence factors, and genomic mutations that hijack angiogenic signaling and drive malignant growth. Concurrently, an elaborate and highly regulated model of angiogenesis and lymphangiogenesis involving vascular endothelial growth factor–receptor tyrosine kinase and TGF-β and Notch pathways has emerged that informs treatment of these tumors as well as cancer in general. This review summarizes the literature on malignant vascular sarcomas in the context of current models of angiogenesis and, in light of recent clinical trial data, could help clinician-scientists generate novel therapeutic approaches.

Environmental chemicals and breast cancer: An updated review of epidemiological literature informed by biological mechanisms

BACKGROUND

Many common environmental chemicals are mammary gland carcinogens in animal studies, activate relevant hormonal pathways, or enhance mammary gland susceptibility to carcinogenesis. Breast cancer's long latency and multifactorial etiology make evaluation of these chemicals in humans challenging.

OBJECTIVE

For chemicals previously identified as mammary gland toxicants, we evaluated epidemiologic studies published since our 2007 review. We assessed whether study designs captured relevant exposures and disease features suggested by toxicological and biological evidence of genotoxicity, endocrine disruption, tumor promotion, or disruption of mammary gland development.

METHODS

We systematically searched the PubMed database for articles with breast cancer outcomes published in 2006-2016 using terms for 134 environmental chemicals, sources, or biomarkers of exposure. We critically reviewed the articles.

RESULTS

We identified 158 articles. Consistent with experimental evidence, a few key studies suggested higher risk for exposures during breast development to dichlorodiphenyltrichloroethane (DDT), dioxins, perfluorooctane-sulfonamide (PFOSA), and air pollution (risk estimates ranged from 2.14 to 5.0), and for occupational exposure to solvents and other mammary carcinogens, such as gasoline components (risk estimates ranged from 1.42 to 3.31). Notably, one 50-year cohort study captured exposure to DDT during several critical windows for breast development (in utero, adolescence, pregnancy) and when this chemical was still in use. Most other studies did not assess exposure during a biologically relevant window or specify the timing of exposure. Few studies considered genetic variation, but the Long Island Breast Cancer Study Project reported higher breast cancer risk for polycyclic aromatic hydrocarbons (PAHs) in women with certain genetic variations, especially in DNA repair genes.

CONCLUSIONS

New studies that targeted toxicologically relevant chemicals and captured biological hypotheses about genetic variants or windows of breast susceptibility added to evidence of links between environmental chemicals and breast cancer. However, many biologically relevant chemicals, including current-use consumer product chemicals, have not been adequately studied in humans. Studies are challenged to reconstruct exposures that occurred decades before diagnosis or access biological samples stored that long. Other problems include measuring rapidly metabolized chemicals and evaluating exposure to mixtures.

Use of CRISPR-modified human stem cell organoids to study the origin of mutational signatures in cancer

Mutational processes underlie cancer initiation and progression. Signatures of these processes in cancer genomes may explain cancer etiology and could hold diagnostic and prognostic value. We developed a strategy that can be used to explore the origin of cancer-associated mutational signatures. We used CRISPR-Cas9 technology to delete key DNA repair genes in human colon organoids, followed by delayed subcloning and whole-genome sequencing. We found that mutation accumulation in organoids deficient in the mismatch repair gene MLH1 is driven by replication errors and accurately models the mutation profiles observed in mismatch repair-deficient colorectal cancers. Application of this strategy to the cancer predisposition gene NTHL1, which encodes a base excision repair protein, revealed a mutational footprint (signature 30) previously observed in a breast cancer cohort. We show that signature 30 can arise from germline NTHL1 mutations.

Genomic Evolution of Breast Cancer Metastasis and Relapse

Patterns of genomic evolution between primary and metastatic breast cancer have not been studied in large numbers, despite patients with metastatic breast cancer having dismal survival. We sequenced whole genomes or a panel of 365 genes on 299 samples from 170 patients with locally relapsed or metastatic breast cancer. Several lines of analysis indicate that clones seeding metastasis or relapse disseminate late from primary tumors, but continue to acquire mutations, mostly accessing the same mutational processes active in the primary tumor. Most distant metastases acquired driver mutations not seen in the primary tumor, drawing from a wider repertoire of cancer genes than early drivers. These include a number of clinically actionable alterations and mutations inactivating SWI-SNF and JAK2-STAT3 pathways.

A pooled mutational analysis identifies ionizing radiation-associated mutational signatures conserved between mouse and human malignancies

Single nucleotide variants (SNVs) identified in cancer genomes can be de-convolved using non-negative matrix factorization (NMF) into discrete trinucleotide-based mutational signatures indicative of specific cancer-causing processes. The stability of NMF-generated mutational signatures depends upon the numbers of variants available for analysis. In this work, we sought to assess whether data from well-controlled mouse models can compensate for scarce human data for some cancer types. High quality sequencing data from radiotherapy-induced cancers is particularly scarce and the mutational processes defining ionizing radiation (IR)-induced mutagenesis in vivo are poorly defined. Here, we combine sequencing data from mouse models of IR-induced malignancies and human IR-induced malignancies. To determine whether the signatures identified from IR-exposed subjects can be differentiated from other mutagenic signatures, we included data from an ultraviolet radiation (UV)-induced human skin cancer and from a mouse model of urethane-induced cancers. NMF distinguished all three mutagens and in the pooled analysis IR was associated with mutational signatures common to both species. These findings illustrate the utility of pooled analysis of mouse and human sequencing data.

Therapeutic radiation for childhood cancer drives structural aberrations of NF2 in meningiomas

Cranial radiotherapy improves survival of the most common childhood cancers, including brain tumors and leukemia. Unfortunately, long-term survivors are faced with consequences of secondary neoplasia, including radiation-induced meningiomas (RIMs). We characterized 31 RIMs with exome/NF2 intronic sequencing, RNA sequencing and methylation profiling, and found NF2 gene rearrangements in 12/31 of RIMs, an observation previously unreported in sporadic meningioma (SM). Additionally, known recurrent mutations characteristic of SM, including AKT1, KLF4, TRAF7 and SMO, were not observed in RIMs. Combined losses of chromosomes 1p and 22q were common in RIMs (16/18 cases) and overall, chromosomal aberrations were more complex than that observed in SM. Patterns of DNA methylation profiling supported similar cell of origin between RIMs and SMs. The findings indicate that the mutational landscape of RIMs is distinct from SMs, and have significant therapeutic implications for survivors of childhood cranial radiation and the elucidation of the molecular pathogenesis of meningiomas.

Radiation-induced meningiomas are often more aggressive than sporadic ones. In this study, the authors perform an exome, methylation and RNA-seq analysis of 31 cases of radiation-induced meningioma and show NF2 rearrangement, an observation previously unreported in the sporadic tumors.

Complex DNA Damage: A Route to Radiation-Induced Genomic Instability and Carcinogenesis

Cellular effects of ionizing radiation (IR) are of great variety and level, but they are mainly damaging since radiation can perturb all important components of the cell, from the membrane to the nucleus, due to alteration of different biological molecules ranging from lipids to proteins or DNA. Regarding DNA damage, which is the main focus of this review, as well as its repair, all current knowledge indicates that IR-induced DNA damage is always more complex than the corresponding endogenous damage resulting from endogenous oxidative stress. Specifically, it is expected that IR will create clusters of damage comprised of a diversity of DNA lesions like double strand breaks (DSBs), single strand breaks (SSBs) and base lesions within a short DNA region of up to 15–20 bp. Recent data from our groups and others support two main notions, that these damaged clusters are: (1) repair resistant, increasing genomic instability (GI) and malignant transformation and (2) can be considered as persistent “danger” signals promoting chronic inflammation and immune response, causing detrimental effects to the organism (like radiation toxicity). Last but not least, the paradigm shift for the role of radiation-induced systemic effects is also incorporated in this picture of IR-effects and consequences of complex DNA damage induction and its erroneous repair.

ISOWN: accurate somatic mutation identification in the absence of normal tissue controls

Background

A key step in cancer genome analysis is the identification of somatic mutations in the tumor. This is typically done by comparing the genome of the tumor to the reference genome sequence derived from a normal tissue taken from the same donor. However, there are a variety of common scenarios in which matched normal tissue is not available for comparison.

Results

In this work, we describe an algorithm to distinguish somatic single nucleotide variants (SNVs) in next-generation sequencing data from germline polymorphisms in the absence of normal samples using a machine learning approach. Our algorithm was evaluated using a family of supervised learning classifications across six different cancer types and ~1600 samples, including cell lines, fresh frozen tissues, and formalin-fixed paraffin-embedded tissues; we tested our algorithm with both deep targeted and whole-exome sequencing data. Our algorithm correctly classified between 95 and 98% of somatic mutations with F1-measure ranges from 75.9 to 98.6% depending on the tumor type. We have released the algorithm as a software package called ISOWN (Identification of SOmatic mutations Without matching Normal tissues).

Conclusions

In this work, we describe the development, implementation, and validation of ISOWN, an accurate algorithm for predicting somatic mutations in cancer tissues in the absence of matching normal tissues. ISOWN is available as Open Source under Apache License 2.0 from https://github.com/ikalatskaya/ISOWN.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-017-0446-9) contains supplementary material, which is available to authorized users.

Molecular signatures in breast cancer

The use of molecular signatures to add value to standard clinical and pathological parameters has impacted clinical practice in many cancer types, but perhaps most notably in the breast cancer field. This is, in part, due to the considerable complexity of the disease at the clinical, morphological and molecular levels. The adoption of molecular profiling of DNA, RNA and protein continues to reveal important differences in the intrinsic biology between molecular subtypes and has begun to impact the way patients are managed. Several bioinformatic tools have been developed using DNA or RNA-based signatures to stratify the disease into biologically and/or clinically meaningful subgroups. Here, we review the approaches that have been used to develop gene expression signatures into currently available diagnostic assays (e.g., OncotypeDX® and Mammaprint®), plus we describe the latest work on genome sequencing, the methodologies used in the discovery process of mutational signatures, and the potential of these signatures to impact the clinic.

Recurrent mutation of IGF signalling genes and distinct patterns of genomic rearrangement in osteosarcoma

Osteosarcoma is a primary malignancy of bone that affects children and adults. Here, we present the largest sequencing study of osteosarcoma to date, comprising 112 childhood and adult tumours encompassing all major histological subtypes. A key finding of our study is the identification of mutations in insulin-like growth factor (IGF) signalling genes in 8/112 (7%) of cases. We validate this observation using fluorescence in situ hybridization (FISH) in an additional 87 osteosarcomas, with IGF1 receptor (IGF1R) amplification observed in 14% of tumours. These findings may inform patient selection in future trials of IGF1R inhibitors in osteosarcoma. Analysing patterns of mutation, we identify distinct rearrangement profiles including a process characterized by chromothripsis and amplification. This process operates recurrently at discrete genomic regions and generates driver mutations. It may represent an age-independent mutational mechanism that contributes to the development of osteosarcoma in children and adults alike.

Significance of Wild-Type p53 Signaling in Suppressing Apoptosis in Response to Chemical Genotoxic Agents: Impact on Chemotherapy Outcome

Our genomes are subject to potentially deleterious alterations resulting from endogenous sources (e.g., cellular metabolism, routine errors in DNA replication and recombination), exogenous sources (e.g., radiation, chemical agents), and medical diagnostic and treatment applications. Genome integrity and cellular homeostasis are maintained through an intricate network of pathways that serve to recognize the DNA damage, activate cell cycle checkpoints and facilitate DNA repair, or eliminate highly injured cells from the proliferating population. The wild-type p53 tumor suppressor and its downstream effector p21^WAF1 (p21) are key regulators of these responses. Although extensively studied for its ability to control cell cycle progression, p21 has emerged as a multifunctional protein capable of downregulating p53, suppressing apoptosis, and orchestrating prolonged growth arrest through stress-induced premature senescence. Studies with solid tumors and solid tumor-derived cell lines have revealed that such growth-arrested cancer cells remain viable, secrete growth-promoting factors, and can give rise to progeny with stem-cell-like properties. This article provides an overview of the mechanisms by which p53 signaling suppresses apoptosis following genotoxic stress, facilitating repair of genomic injury under physiological conditions but having the potential to promote tumor regrowth in response to cancer chemotherapy.

Risk of secondary cancers: Bridging epidemiology and modeling

Epidemiological studies of long term radiotherapy survivors provide useful insights into dose-response relationships for secondary cancer induction risk at high doses. There are uncertainties involved in estimating the dose to the location of the second malignancy, because the dose distributions in radiotherapy patients can be spatially highly heterogeneous and the size of the diagnosed tumor is on the order of a few cm. Therefor it is nearly impossible to obtain the exact dose corresponding to the exact tumor induction location and so organ specific dose-response relationships have large errors not only in the reported risk, but also in the estimated dose. In this work two alternative methods are proposed for future applications involving investigations into dose response relationships for second cancer induction risk, the method of organ sub-division and the method of risk equivalent dose. The method of organ sub-division takes the inevitable inhomogeneous dose distribution into account by applying epidemiological methods to organ sub-divisions which have a nearly homogenous dose. The method of risk equivalent dose combines risk modeling and epidemiological data analysis. Risk models can be optimized by using an iterative procedure assuming a variation of organ specific dose-responses. The advantage of the alternative methods is that the inhomogeneity of the dose in the organs at risk is taken into account. The second method has the additional advantage that the dose to the location of the tumor site must not be known and that epidemiologically obtained risks that were not stratified by organ specific risk can be used.

Ionizing radiation biomarkers in epidemiological studies - An update

Recent epidemiology studies highlighted the detrimental health effects of exposure to low dose and low dose rate ionizing radiation (IR): nuclear industry workers studies have shown increased leukaemia and solid tumour risks following cumulative doses of <100mSv and dose rates of <10mGy per year; paediatric patients studies have reported increased leukaemia and brain tumours risks after doses of 30-60mGy from computed tomography scans. Questions arise, however, about the impact of even lower doses and dose rates where classical epidemiological studies have limited power but where subsets within the large cohorts are expected to have an increased risk. Further progress requires integration of biomarkers or bioassays of individual exposure, effects and susceptibility to IR. The European DoReMi (Low Dose Research towards Multidisciplinary Integration) consortium previously reviewed biomarkers for potential use in IR epidemiological studies. Given the increased mechanistic understanding of responses to low dose radiation the current review provides an update covering technical advances and recent studies. A key issue identified is deciding which biomarkers to progress. A roadmap is provided for biomarker development from discovery to implementation and used to summarise the current status of proposed biomarkers for epidemiological studies. Most potential biomarkers remain at the discovery stage and for some there is sufficient evidence that further development is not warranted. One biomarker identified in the final stages of development and as a priority for further research is radiation specific mRNA transcript profiles.