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BackgroundDespite their large numbers and widespread use, very little is known about the extent to which per- and polyfluoroalkyl substances (PFAS) can cross the placenta and expose the developing fetus.ObjectiveThe aim of our study is to develop a computational approach that can be used to evaluate the of extend to which small molecules, and in particular PFAS, can cross to cross the placenta and partition to cord blood.MethodsWe collected experimental values of the concentration ratio between cord and maternal blood (RCM) for 260 chemical compounds and calculated their physicochemical descriptors using the cheminformatics package Mordred. Weused the compiled database to, train and test an artificial neural network (ANN). And then applied the best performing model to predict RCM for a large dataset of PFAS chemicals (n = 7982). We, finally, examined the calculatedphysicochemical descriptors of the chemicals to identify which properties correlated significantly with RCM.ResultsWe determined that 7855 compounds were within the applicability domain and 127 compounds are outside the applicability domain of our model. Our predictions of RCM for PFAS suggested that 3623 compounds had a log RCM > 0 indicating preferable partitioning to cord blood. Some examples of these compounds were bisphenol AF, 2,2-bis(4-aminophenyl)hexafluoropropane, and nonafluoro-tert-butyl 3-methylbutyrate.SignificanceThese observations have important public health implications as many PFAS have been shown to interfere with fetal development.In addition, asthese compounds are highly persistent and many of them can readilycross the placenta,they are expected to remain in the population for a long time as they are being passed from parent to offspring.ImpactUnderstanding the behavior of chemicals in the human body during pregnancy is critical in preventing harmful exposures during critical periods of development. Many chemicals can cross the placenta and expose the fetus, however, the mechanism by which this transport occurs is not well understood. In our study, we developed a machine learning model that describes the transplacental transfer of chemicals as a function of their physicochemical properties. The model was then used to make predictions for a set of 7982 per-and polyfluorinated alkyl substances that are listed on EPA's CompTox Chemicals Dashboard.The model can be applied to make predictions for other chemical categories of interest, such as plasticizers and pesticides. Accurate predictions of RCMcan help scientists and regulators to prioritize chemicals that have the potential to cause harm by exposing the fetus.

Since the inception of the IARC Monographs Programme in the early 1970s, this Programme has developed 119 Monograph Volumes on more than 1000 agents for which there exists some evidence of cancer risk to humans. Of these, 120 agents were found to meet the criteria for classification as carcinogenic to humans (Group 1). Volume 100 of the IARC Monographs, compiled in 2008–2009 and published in 2012, provided a review and update of the 107 Group 1 agents identified as of 2009. These agents were divided into six broad categories: (I) pharmaceuticals; (II) biological agents; (III) arsenic, metals, fibers and dusts; (IV) radiation; (V) personal habits and indoor combustions; and (VI) chemical agents and related occupations. The Group I agents reviewed in Volume 100, as well as five additional Group 1 agents defined in subsequent Volumes of the Monographs, were used to assess the degree of concordance between sites where tumors originate in humans and experimental animals including mice, rats, hamsters, dogs, and non-human primates using an anatomically based tumor nomenclature system, representing 39 tumor sites and 14 organ and tissue systems. This evaluation identified 91 Group 1 agents with sufficient evidence (82 agents) or limited evidence (9 agents) of carcinogenicity in animals. The most common tumors observed in both humans and animals were those of the respiratory system including larynx, lung, and lower respiratory tract. In humans, respiratory system tumors were noted for 31 of the 111 distinct Group 1 carcinogens identified up to and including Volume 109 of the IARC Monographs, comprising predominantly 14 chemical agents and related occupations in category VI; seven arsenic, metals, fibers, and dusts in category III, and five personal habits and indoor combustions in category V. Subsequent to respiratory system tumors, those in lymphoid and hematopoietic tissues (26 agents), the urothelium (18 agents), and the upper aerodigestive tract (16 agents) were most often seen in humans, while tumors in digestive organs (19 agents), skin (18 agents), and connective tissues (17 agents) were frequently seen in animals. Exposures to radiation, particularly X- and γ-radiation, and tobacco smoke were associated with tumors at multiple sites in humans. Although the IARC Monographs did not emphasize tumor site concordance between animals and humans, substantial concordance was detected for several organ and tissue systems, even under the stringent criteria for sufficient evidence of carcinogenicity used by IARC. Of the 60 agents for which at least one tumor site was identified in both humans and animals, 52 (87%) exhibited tumors in at least one of the same organ and tissue systems in humans and animals. It should be noted that some caution is needed in interpreting concordance at sites where sample size is particularly small. Although perfect (100%) concordance was noted for agents that induce tumors of the mesothelium, only two Group 1 agents that met the criteria for inclusion in the concordance analysis caused tumors at this site. Although the present analysis demonstrates good concordance between animals and humans for many, but not all, tumor sites, limitations of available data may result in underestimation of concordance.

Endocrine-disrupting chemicals (EDCs) are exogenous chemicals that interfere with hormone action, thereby increasing the risk of adverse health outcomes, including cancer, reproductive impairment, cognitive deficits and obesity. A complex literature of mechanistic studies provides evidence on the hazards of EDC exposure, yet there is no widely accepted systematic method to integrate these data to help identify EDC hazards. Inspired by work to improve hazard identification of carcinogens using key characteristics (KCs), we have developed ten KCs of EDCs based on our knowledge of hormone actions and EDC effects. In this Expert Consensus Statement, we describe the logic by which these KCs are identified and the assays that could be used to assess several of these KCs. We reflect on how these ten KCs can be used to identify, organize and utilize mechanistic data when evaluating chemicals as EDCs, and we use diethylstilbestrol, bisphenol A and perchlorate as examples to illustrate this approach., In this Expert Consensus Statement, the authors define 10 key characteristics (KCs) for endocrine-disrupting chemicals. They further describe the logic by which these KCs are identified and the assays that could be used to assess several of these KCs.

Since the inception of the International Agency for Research on Cancer (IARC) in the early 1970s, the IARC Monographs Programme has evaluated more than 1000 agents with respect to carcinogenic hazard; of these, up to and including Volume 119 of the IARC Monographs, 120 agents met the criteria for classification as carcinogenic to humans (Group 1). Volume 100 of the IARC Monographs provided a review and update of Group 1 carcinogens. These agents were divided into six broad categories: (I) pharmaceuticals; (II) biological agents; (III) arsenic, metals, fibers, and dusts; (IV) radiation; (V) personal habits and indoor combustions; and (VI) chemical agents and related occupations. Data on biological mechanisms of action (MOA) were extracted from the Monographs to assemble a database on the basis of ten key characteristics attributed to human carcinogens. After some grouping of similar agents, the characteristic profiles were examined for 86 Group 1 agents for which mechanistic information was available in the IARC Monographs up to and including Volume 106, based upon data derived from human in vivo, human in vitro, animal in vivo, and animal in vitro studies. The most prevalent key characteristic was "is genotoxic", followed by "alters cell proliferation, cell death, or nutrient supply" and "induces oxidative stress". Most agents exhibited several of the ten key characteristics, with an average of four characteristics per agent, a finding consistent with the notion that cancer development in humans involves multiple pathways. Information on the key characteristics was often available from multiple sources, with many agents demonstrating concordance between human and animal sources, particularly with respect to genotoxicity. Although a detailed comparison of the characteristics of different types of agents was not attempted here, the overall characteristic profiles for pharmaceutical agents and for chemical agents and related occupations appeared similar. Further in-depth analyses of this rich database of characteristics of human carcinogens are expected to provide additional insights into the MOA of human cancer development.

Volume 100 in the series of IARC Monographs on the Evaluation of Carcinogenic Risks to Humans comprises an update and review of relevant information on all agents determined to induce cancer in humans. These Group 1 agents are categorized in 6 Monographs (Volumes 100A-F) published in 2012. This paper describes the methodology and stringent criteria used in the creation of a comprehensive database on tumors noted in animals and humans for the carcinogens reviewed in Volume 100, and for additional Group 1 agents that were identified in subsequent Monographs through Volume 109. The development of this database involved the systematic collection of relevant data on tumors detected in humans and experimental animals identified by the Working Groups that conducted evaluations reported in the IARC Monographs. The database includes all human tumor sites identified by the Working Groups, along with all tumor sites for which there was sufficient evidence in experimental animals. This database provides a basis for assessing the degree of concordance between tumor sites observed in humans and experimental animals for Group 1 agents identified through Volume 109.

The Evidence-based Toxicology Collaboration hosted a workshop on "The Emergence of Systematic Review and Related Evidence-based Approaches in Toxicology," on November 21, 2014 in Baltimore, Maryland. The workshop featured speakers from agencies and organizations applying systematic review approaches to questions in toxicology, speakers with experience in conducting systematic reviews in medicine and healthcare, and stakeholders in industry, government, academia, and non-governmental organizations. Based on the workshop presentations and discussion, here we address the state of systematic review methods in toxicology, historical antecedents in both medicine and toxicology, challenges to the translation of systematic review from medicine to toxicology, and thoughts on the way forward. We conclude with a recommendation that as various agencies and organizations adapt systematic review methods, they continue to work together to ensure that there is a harmonized process for how the basic elements of systematic review methods are applied in toxicology. published

Background: A recent review by the International Agency for Research on Cancer (IARC) updated the assessments of the > 100 agents classified as Group 1, carcinogenic to humans (IARC Monographs Volume 100, parts A–F). This exercise was complicated by the absence of a broadly accepted, systematic method for evaluating mechanistic data to support conclusions regarding human hazard from exposure to carcinogens. Objectives and Methods: IARC therefore convened two workshops in which an international Working Group of experts identified 10 key characteristics, one or more of which are commonly exhibited by established human carcinogens. Discussion: These characteristics provide the basis for an objective approach to identifying and organizing results from pertinent mechanistic studies. The 10 characteristics are the abilities of an agent to 1) act as an electrophile either directly or after metabolic activation; 2) be genotoxic; 3) alter DNA repair or cause genomic instability; 4) induce epigenetic alterations; 5) induce oxidative stress; 6) induce chronic inflammation; 7) be immunosuppressive; 8) modulate receptor-mediated effects; 9) cause immortalization; and 10) alter cell proliferation, cell death, or nutrient supply. Conclusion: We describe the use of the 10 key characteristics to conduct a systematic literature search focused on relevant end points and construct a graphical representation of the identified mechanistic information. Next, we use benzene and polychlorinated biphenyls as examples to illustrate how this approach may work in practice. The approach described is similar in many respects to those currently being implemented by the U.S. EPA’s Integrated Risk Information System Program and the U.S. National Toxicology Program. Citation: Smith MT, Guyton KZ, Gibbons CF, Fritz JM, Portier CJ, Rusyn I, DeMarini DM, Caldwell JC, Kavlock RJ, Lambert P, Hecht SS, Bucher JR, Stewart BW, Baan R, Cogliano VJ, Straif K. 2016. Key characteristics of carcinogens as a basis for organizing data on mechanisms of carcinogenesis. Environ Health Perspect 124:713–721; http://dx.doi.org/10.1289/ehp.1509912

Information on the causes of cancer at specific sites is important to cancer control planners, cancer researchers, cancer patients, and the general public. The International Agency for Research on Cancer (IARC) Monograph series, which has classified human carcinogens for more than 40 years, recently completed a review to provide up-to-date information on the cancer sites associated with more than 100 carcinogenic agents. Based on IARC’s review, we listed the cancer sites associated with each agent and then rearranged this information to list the known and suspected causes of cancer at each site. We also summarized the rationale for classifications that were based on mechanistic data. This information, based on the forthcoming IARC Monographs Volume 100, offers insights into the current state-of-the-science of carcinogen identification. Use of mechanistic data to identify carcinogens is increasing, and epidemiological research is identifying additional carcinogens and cancer sites or confirming carcinogenic potential under conditions of lower exposure. Nevertheless, some common human cancers still have few (or no) identified causal agents.

We conducted a meta-analysis to quantitatively compare the association between occupation as a painter and the incidence or mortality from lung cancer. PubMed and the reference lists of pertinent publications were searched and reviewed. For the meta-analysis, we used data from 47 independent cohort, record linkage, and case-control studies (from a total of 74 reports), including > 11,000 incident cases or deaths from lung cancer among painters. Three authors independently abstracted data and assessed study quality. The summary relative risk (meta-RR, random effects) for lung cancer in paint-ers was 1.35 [95% confidence interval (CI), 1.29-1.41; 47 studies] and 1.35 (95% CI, 1.21-1.51; 27 studies) after controlling for smoking. The relative risk was higher in never-smokers (meta-RR = 2.00; 95% CI, 1.09-3.67; 3studies) and persisted when restricted to studies that adjusted for other occupational exposures (meta-RR = 1.57; 95% CI, 1.21-2.04; 5 studies). These results support the conclusion that occupational exposures in painters are causally associated with the risk of lung cancer.Conduziu-se uma meta-análise para comparar quatitativamente a associação entre o trabalho de pintor e a incidência ou mortalidade por câncer de pulmão. PubMed e listas de referência de publicações pertinentes foram pesquisadas e revisadas. Para a análise, foram usados dados de 47 estudos de caso, coorte independente e ligação de dados (de um total de 74 relatórios), incluindo > 11 mil casos de incidentes ou morte por câncer de pulmão entre pintores. Três autores coletaram dados e avaliaram a qualidade de estudo. O risco relativo (meta-RR, efeitos aleatórios) de câncer de pulmão em pintores foi de 1,35 [95% intervalo de confiança (IC), 1,29-1,41; 47 estudos] e 1,35 (95% IC, 1,21-1,51; 27 estudos) depois de se destacar os fumantes. O risco relativo foi maior naqueles que nunca fumaram (meta-RR = 2.00; 95% CI, 1,09-3,67; 3 estudos) e persistiu quanto restringido a estudos que foram ajustados para outras exposições ocupacionais (meta-RR = 1,57; 95% CI, 1,21-2,04; 5 estudos). Estes resultados sustentam a conclusão de que exposições ocupacionais em pintores são causadamente associada com o risco de câncer de pulmão.

Objectives There are some common occupational agents and exposure circumstances for which evidence of carcinogenicity is substantial but not yet conclusive for humans. Our objectives were to identify research gaps and needs for 20 agents prioritized for review based on evidence of widespread human exposures and potential carcinogenicity in animals or humans. Data sources For each chemical agent (or category of agents), a systematic review was conducted of new data published since the most recent pertinent International Agency for Research on Cancer (IARC) Monograph meeting on that agent. Data extraction Reviewers were charged with identifying data gaps and general and specific approaches to address them, focusing on research that would be important in resolving classification uncertainties. An expert meeting brought reviewers together to discuss each agent and the identified data gaps and approaches. Data synthesis Several overarching issues were identified that pertained to multiple agents; these included the importance of recognizing that carcinogenic agents can act through multiple toxicity pathways and mechanisms, including epigenetic mechanisms, oxidative stress, and immuno- and hormonal modulation. Conclusions Studies in occupational populations provide important opportunities to understand the mechanisms through which exogenous agents cause cancer and intervene to prevent human exposure and/or prevent or detect cancer among those already exposed. Scientific developments are likely to increase the challenges and complexities of carcinogen testing and evaluation in the future, and epidemiologic studies will be particularly critical to inform carcinogen classification and risk assessment processes.

While scientific knowledge of the potential health significance of chemical exposures has grown, experimental methods for predicting the carcinogenicity of environmental agents have not been substantially updated in the last two decades. Current methodologies focus first on identifying genotoxicants under the premise that agents capable of directly damaging DNA are most likely to be carcinogenic to humans. Emphasis on the distinction between genotoxic and non-genotoxic carcinogens is also motivated by assumed implications for the dose-response curve; it is purported that genotoxicants would lack a threshold in the low dose region, in contrast to non-genotoxic agents. However, for the vast majority of carcinogens, little if any empirical data exist to clarify the nature of the cancer dose-response relationship at low doses in the exposed human population. Recent advances in scientific understanding of cancer biology-and increased appreciation of the multiple impacts of carcinogens on this disease process-support the view that environmental chemicals can act through multiple toxicity pathways, modes and/or mechanisms of action to induce cancer and other adverse health outcomes. Moreover, the relationship between dose and a particular outcome in an individual could take multiple forms depending on genetic background, target tissue, internal dose and other factors besides mechanisms or modes of action; inter-individual variability and susceptibility in response are, in turn, key determinants of the population dose-response curve. New bioanalytical approaches (e.g., transcriptomics, proteomics, and metabolomics) applied in human, animal and in vitro studies could better characterize a wider array of hazard traits and improve the ability to predict the potential carcinogenicity of chemicals.

BACKGROUND: Assessing adverse effects from environmental chemical exposure is integral to public health policies. Toxicology assays identifying early biological changes from chemical exposure are increasing our ability to evaluate links, between early biological disturbances and subsequent overt downstream effects. A workshop was held to consider how the resulting data inform consideration of an "adverse effect" in the context of hazard identification and risk assessment. OBJECTIVES: Our objective here is to review what is known about the relationships between chemical exposure, early biological effects (Upstream events), and later overt effects (downstream events) through three case studies (thyroid hormone disruption, antiandrogen effects, immune system disruption) and to consider how to evaluate hazard and risk when early biological effect data are available. DISCUSSION: Each case study presents data on the toxicity pathways linking early biological perturbations with downstream overt effects. Case studies also emphasize several factors that can influence risk of overt disease as a result from early biological perturbations, including background chemical exposures, underlying individual biological processes, and disease susceptibility. Certain effects resulting from exposure during periods of sensitivity may, be irreversible. A chemical can act through multiple modes of action, resulting in similar or different overt effects. CONCLUSIONS: For certain classes of early perturbations, Sufficient information oil the disease process is known, so hazard and quantitative risk assessment can proceed using information on upstream biological perturbations. Upstream data will Support improved approaches for considering developmental stage, background exposures, disease status, and other factors important to assessing hazard and risk for the whole population

Health risk assessments generally involve many extrapolations: for example, from animals to humans or from high doses to lower doses. Health risk assessments for PCBs involve all the usual uncertainties, plus additional uncertainties due to the nature of PCBs as a dynamic, complex mixture. Environmental processes alter PCB mixtures after release into the environment, so that people are exposed to mixtures that might not resemble the mixtures where there are toxicity data. This paper discusses the evolution of understanding in assessments of the cancer and noncancer effects of PCBs. It identifies where a lack of data in the past contributed to significant uncertainty and where new data subsequently altered the prevailing understanding of the toxicity of PCB mixtures, either qualitatively or quantitatively. Finally, the paper identifies some uncertainties remaining for current PCB health assessments, particularly those that result from a lack of data on exposure through nursing or on effects from inhalation of PCBs.

An international, interdisciplinary working group of expert scientists met in June 2004 to develop IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans (IARC Monographs) on formaldehyde, 2-butoxyethanol, and 1-tert-butoxy-2-propanol. Each IARC Monograph includes a critical review of the pertinent scientific literature and an evaluation of an agent’s potential to cause cancer in humans. After a thorough discussion of the epidemiologic, experimental, and other relevant data, the working group concluded that formaldehyde is carcinogenic to humans, based on sufficient evidence in humans and in experimental animals. In the epidemiologic studies, there was sufficient evidence that formaldehyde causes nasopharyngeal cancer, “strong but not sufficient” evidence of leukemia, and limited evidence of sinonasal cancer. The working group also concluded that 2-butoxyethanol and 1-tert-butoxy-2-propanol are not classifiable as to their carcinogenicity to humans, each having limited evidence in experimental animals and inadequate evidence in humans. These three evaluations and the supporting data will be-published as Volume 88 of the IARC Monographs.

Several national and international health agencies have established programs with the aim of identifying agents and exposures that cause cancer in humans. Carcinogen identification is an activity grounded in the scientific evaluation of the results of human epidemiologic studies, long-term bioassays in experimental animals, and other data relevant to an evaluation of carcinogenicity and its mechanisms. In this commentary, after a brief discussion of the science basis common to the evaluation of carcinogens across different programs, we discuss in more detail the principles and procedures currently used by the IARC Monographs program.

The views expressed in this paper are those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency. Assessments of TCE's potential to cause cancer in humans have had to address issues concerning the strength of the human evidence and the relevance of the animal tumors to humans. The epidemiological database now includes analyses of multiple studies and molecular information. A recent analysis strongly suggests that TCE may induce cancer in humans at multiple sites, including kidney, liver, and lympho-hematopoietic cancer. Molecular analyses have found mutations of the von Hippel-Lindau tumor suppressor gene in renal tumors of TCE-exposed individuals. The animal bioassays have been followed up with mechanistic studies that provide insight into TCE's possible modes of action at each tumor site. This information suggests that TCE may act through mechanisms that can be relevant to human cancers. The mechanistic information can also be used to identify r...

A public health concern regarding hazardous air pollutants (HAPs) is their potential to cause cancer. It has been difficult to assess potential cancer risks from HAPs, due primarily to lack of ambient concentration data for the general population. The Environmental Protection Agency's Cumulative Exposure Project modeled 1990 outdoor concentrations of HAPs across the United States, which were combined with inhalation unit risk estimates to estimate the potential increase in excess cancer risk for individual carcinogenic HAPs. These were summed to provide an estimate of cancer risk from multiple HAPs. The analysis estimates a median excess cancer risk of 18 lifetime cancer cases per 100,000 people for all HAP concentrations. About 75% of estimated cancer risk was attributable to exposure to polycyclic organic matter, 1,3-butadiene, formaldehyde, benzene, and chromium. Consideration of some specific uncertainties, including underestimation of ambient concentrations, combining upper 95% confidence bound potency estimates, and changes to potency estimates, found that cancer risk may be underestimated by 15% or overestimated by 40-50%. Other unanalyzed uncertainties could make these under- or overestimates larger. This analysis used 1990 estimates of concentrations and can be used to track progress toward reducing cancer risk to the general population.

A new approach to assessing the cancer risk from environmental polychlorinated biphenyls (PCBs) considers both toxicity and environmental processes to make distinctions among environmental mixtures. New toxicity information from a 1996 cancer study of four commercial mixtures strengthens the case that all PCB mixtures can cause cancer, although different mixtures have different potencies. Environmental processes alter PCB mixtures through partitioning, chemical transformation, and preferential bioaccumulation; these processes can increase or decrease toxicity considerably. Bioaccumulated PCBs are of greatest concern because they appear to be more toxic than commercial PCBs and more persistent in the body. The new approach uses toxicity studies of commercial mixtures to develop a range of cancer potency estimates and then considers the effect of environmental processes to choose appropriate values for representative classes of environmental mixtures. Guidance is given for assessing risks from different exposure pathways, less-than-lifetime and early-life exposures, and mixtures containing dioxinlike compounds.

Quantitative cancer risk assessments are typically expressed as plausible upper bounds rather than estimates of central tendency. In analyses involving several carcinogens, these upper bounds are often summed to estimate overall risk. This begs the question of whether a sum of upper bounds is itself a plausible estimate of overall risk. This question can be asked in two ways: whether the sum yields an improbable estimate of overall risk (that is, is it only remotely possible for the true sum of risks to match the sum of upper bounds), or whether the sum gives a misleading estimate (that is, is the true sum of risks likely to be very different from the sum of upper bounds). Analysis of four case studies shows that as the number of risk estimates increases, their sum becomes increasingly improbable, but not misleading. Though the overall risk depends on the independence, additivity, and number of risk estimates, as well as the shapes of the underlying risk distributions, sums of upper bounds provide useful information about the overall risk and can be adjusted downward to give a more plausible [perhaps probable] upper bound, or even a central estimate of overall risk.

Trichloroethylene (TCE), an environmental contaminant of National concern, is the focus of a new health risk assessment process incorporating the Proposed Cancer Risk Assessment Guidelines. This paper describes not only how TCE became an environmental problem for the Air Force, but also details the new Risk Assessment process envisioned by the Environmental Protection Agency's (EPA) National Center for Environmental Assessment (NCEA). Insights on epidemiological evaluations, both past and future, and their impact on the cancer classification of TCE are discussed. Examples of how physiologically based pharmacokinetics and dose-response characterization described in the new Cancer Guidelines are applied to TCE are provided. In addition, a variety of modeling techniques are discussed for the development of reference doses (oral exposure) and reference concentrations (inhalation exposures) for TCE. Finally, the role of risk communication is included. This new process provides an example of how interagency (EPA, Department of Defense. Department of Energy) and extramural (industry, academia) partnerships can provide greater gains to the nation, as a whole, than any of the parts on their own.

We propose guidelines to evaluate the cumulative evidence of gene-environment (G × E) interactions in the causation of human cancer. Our approach has its roots in the HuGENet and IARC Monographs evaluation processes for genetic and environmental risk factors, respectively, and can be applied to common chronic diseases other than cancer. We first review issues of definitions of G × E interactions, discovery and modelling methods for G × E interactions, and issues in systematic reviews of evidence for G × E interactions, since these form the foundation for appraising the credibility of evidence in this contentious field. We then propose guidelines that include four steps: (i) score the strength of the evidence for main effects of the (a) environmental exposure and (b) genetic variant; (ii) establish a prior score category and decide on the pattern of interaction to be expected; (iii) score the strength of the evidence for interaction between the environmental exposure and the genetic variant; and (iv) examine the overall plausibility of interaction by combining the prior score and the strength of the evidence and interpret results. We finally apply the scheme to the interaction between NAT2 polymorphism and tobacco smoking in determining bladder cancer risk. Published by Oxford University Press on behalf of the International Epidemiological Association © The Author 2012.

The International Agency for Research on Cancer has classified occupational exposure as a painter as ‘carcinogenic to humans’, largely based on increased risks of bladder and lung cancer. A meta-analysis, including more than 2900 incident cases or deaths from bladder cancer among painters reported in 41 cohort (n=2), record linkage (n=9) and case–control (n=30) studies, was conducted to quantitatively compare the results of the different study designs and the potential confounding effect of smoking as well as other occupational exposures. The summary relative risk (meta-RR, random effects) for bladder cancer in painters was 1.25 (95% CI 1.16 to 1.34; 41 studies) overall and 1.28 (95% CI 1.15 to 1.43; 27 studies) when including only smoking adjusted risk estimates. The elevated risk persisted when restricted to studies that adjusted for other occupational exposures (meta-RR 1.27; 95% CI 0.99 to 1.63; 4 studies). The results remained robust when stratified by study design, gender and study location. Furthermore, exposure–response analyses suggested that the risk increased with duration of employment. There was no evidence of publication bias. Taken together, these results support the conclusion that occupational exposures in painters are causally associated with the risk of bladder cancer.

We conducted a meta-analysis to quantitatively compare the association between occupation as a painter and the incidence or mortality from lung cancer. PubMed and the reference lists of pertinent publications were searched and reviewed. For the meta-analysis, we used data from 47 independent cohort, record linkage, and case-control studies (from a total of 74 reports), including > 11,000 incident cases or deaths from lung cancer among painters. Three authors independently abstracted data and assessed study quality. The summary relative risk (meta-RR, random effects) for lung cancer in paint-ers was 1.35 [95% confidence interval (CI), 1.29-1.41; 47 studies] and 1.35 (95% CI, 1.21-1.51; 27 studies) after controlling for smoking. The relative risk was higher in never-smokers (meta-RR = 2.00; 95% CI, 1.09-3.67; 3studies) and persisted when restricted to studies that adjusted for other occupational exposures (meta-RR = 1.57; 95% CI, 1.21-2.04; 5 studies). These results support the conclusion that occupational exposures in painters are causally associated with the risk of lung cancer. Conduziu-se uma meta-análise para comparar quatitativamente a associação entre o trabalho de pintor e a incidência ou mortalidade por câncer de pulmão. PubMed e listas de referência de publicações pertinentes foram pesquisadas e revisadas. Para a análise, foram usados dados de 47 estudos de caso, coorte independente e ligação de dados (de um total de 74 relatórios), incluindo > 11 mil casos de incidentes ou morte por câncer de pulmão entre pintores. Três autores coletaram dados e avaliaram a qualidade de estudo. O risco relativo (meta-RR, efeitos aleatórios) de câncer de pulmão em pintores foi de 1,35 [95% intervalo de confiança (IC), 1,29-1,41; 47 estudos] e 1,35 (95% IC, 1,21-1,51; 27 estudos) depois de se destacar os fumantes. O risco relativo foi maior naqueles que nunca fumaram (meta-RR = 2.00; 95% CI, 1,09-3,67; 3 estudos) e persistiu quanto restringido a estudos que foram ajustados para outras exposições ocupacionais (meta-RR = 1,57; 95% CI, 1,21-2,04; 5 estudos). Estes resultados sustentam a conclusão de que exposições ocupacionais em pintores são causadamente associada com o risco de câncer de pulmão.

Consideration of mechanistic data has the potential to improve the analysis of both epidemiologic studies and cancer bioassays. IARC has a classification system in which mechanistic data can play a pivotal role. Since 1991, IARC has allowed an agent to be classified as carcinogenic to humans (Group 1) when there is less than sufficient evidence in humans but there is sufficient evidence in experimental animals and "strong evidence in exposed humans that the agent acts through a relevant mechanism of carcinogenicity." Mechanistic evidence can also substitute for conventional cancer bioassays when there is less than sufficient evidence in experimental animals, just as mechanistic evidence can substitute for conventional epidemiologic studies when there is less than sufficient evidence in humans. The IARC Monographs have used mechanistic data to raise or lower a classification that would be otherwise based on epidemiologic studies and cancer bioassays only. Recently, the IARC Monographs have evaluated several agents where mechanistic data were pivotal to the overall evaluation: benzo[a]pyrene, carbon black and other poorly soluble particles, ingested nitrates and nitrites, and microcystin-LR. In evaluating mechanistic data, it is important to consider alternative mechanistic hypotheses, because an agent may induce tumors through multiple mechanisms.

Carcinogenicity bioassays generally provide the best means of assessing the potential for a chemical to be a human carcinogenic hazard. The results of carcinogenicity bioassays are usually the key determinants of IARC Monograph evaluations. Along with carcinogenicity bioassays and epidemiological studies, the International Agency for Research on Cancer (IARC) also encourages the consideration of mechanistic data and other relevant data. During 2005 IARC is updating the Preamble to the IARC Monographs, which describes the principles and procedures used in developing the Monographs, including the criteria that guide the evaluations. Proposed revisions to the Preamble make some changes in the criteria for evaluating carcinogenicity in experimental animals to reflect the greater confidence that can be placed in Good Laboratory Practice (GLP) studies. Other changes will give more specific guidance for the evaluation of mechanistic data. Sections on mechanistic data will be given more prominence in future Monographs and will be more closely linked with toxicokinetics. Future Monographs will also include a new section on susceptible individuals, populations, and life stages that will often be based on the understanding of mechanisms. In addition, the draft Preamble discusses IARC's procedures for promoting impartial evaluations by avoiding conflicts of interests and ensuring that working groups are free from interference.

Formaldehyde and glutaraldehyde cause toxicity to the nasal epithelium of rats and mice upon inhalation. In addition, formaldehyde above certain concentrations induces dose-related increases in nasal tumors in rats and mice, but glutaraldehyde does not. Using the 2006 IPCS human framework for the analysis of cancer mode of action (MOA), an MOA for formaldehyde was formulated and its relevance was tested against the properties of the noncarcinogenic glutaraldehyde. These compounds produce similar patterns of response in histopathology and in genotoxicity tests (although formaldehyde has been much more extensively tested studied). The MOA is based on the induction of sustained cytotoxicity and reparative cell proliferation induced by formaldehyde at concentrations that also induce nasal tumors upon long-term exposure. Data on dose dependency and temporal relationships of key events are consistent with this MOA. While a genotoxic MOA can never be ruled out for a compound that is clearly genotoxic, at least in vitro, the nongenotoxic properties fundamental to the proposed MOA can explain the neoplastic response in the nose and may be more informative than genotoxicity in risk assessment. It is not yet fully explained why glutaraldehyde remains noncarcinogenic upon inhalation, but its greater inherent toxicity may be a key factor. The dual aldehyde functions in glutaraldehyde are likely to produce damage resulting in fewer kinetic possibilities (particularly for proteins involved in differentiation control) and lower potential for repair (nucleic acids) than would be the case for formaldehyde. While there have been few studies of possible glutaraldehyde-associated cancer, the evidence that formaldehyde is a human carcinogen is strong for nasopharyngeal cancers, although less so for sinonasal cancers. This apparent discrepancy could be due in part to the classification of human nasal tumors with tumors of the sinuses, which would receive much less exposure to inhaled formaldehyde. Evaluation of the human relevance of the proposed MOA of formaldehyde in rodents is restricted by human data limitations, although the key events are plausible. It is clear that the human relevance of the formaldehyde MOA in rodents cannot be excluded on either kinetic or dynamic grounds.

Commentary on the paper by Sathiakumar et al ( Occup Environ Med , December 2005)* In the December 2005 issue of this journal, Sathiakumar and colleagues1 report on the extended follow up of the University of Alabama cohort in the styrene–butadiene–rubber industry. The update confirms the increased risk of haemato-lymphopoietic malignancies in work areas with high exposure to butadiene and styrene. This study is both potentially informative and at the centre of controversies regarding the evidence for the human carcinogenicity of butadiene and styrene. In 1999, an IARC Working Group concluded that butadiene is “probably carcinogenic to humans” (Group 2A) on the basis of “limited evidence” of carcinogenicity in humans and “sufficient evidence” in experimental animals.2 A case-control study nested in the University of Alabama cohort3 showed a consistent excess of leukaemia and a statistically significant dose–response relationship with cumulative exposure to 1,3-butadiene, which remained after adjustment for exposure to styrene. Studies among workers in butadiene production reported an excess of lymphohaematopoietic cancers. In 2002 a separate IARC Working Group concluded that styrene is “possibly carcinogenic to humans” (Group 2B) on the basis …

Several national and international health agencies worldwide have established carcinogen identification programs with the aim of identifying the agents and exposures that contribute to the global burden of cancer. These programs have many features in common. IARC's program is described in some detail, with an emphasis on how evaluations can be changed by mechanistic data. Recently, several programs have expanded on the guidance they provide in assessing mechanistic data. The most comprehensive example is EPA's recent draft final Guidelines for Carcinogen Risk Assessment. In all programs, however, the principal role of mechanistic information has been to support the positive results observed in epidemiological studies or to discount the relevance of positive results observed in experimental animal bioassays. An alternative paradigm for carcinogen identification is proposed, one where mechanistic studies have a central role, rather than a supporting one. Under this paradigm, potentially carcinogenic agents would be identified by (1) identifying the key precursor events and processes involved in human cancer and (2) testing to see whether an agent can affect these events and processes. Under this paradigm, which is consistent with a multi-factorial view of carcinogenesis, it might be possible to identify carcinogens through mechanistic understanding alone, without waiting for epidemiological studies or 2-year carcinogenesis bioassays in rats and mice. This paradigm asks the question, "What is a human carcinogen? Is it an agent that we observe to induce tumors, or more generally, an agent with a clear role in tumor development?"

In October, 2007, 24 scientists from ten countries met at the International Agency for Research on Cancer (IARC), Lyon, France, to assess the carcinogenicity of shift-work, painting, and fi re-fi ghting. These assessments will be published as volume 98 of the IARC Monographs. About 15–20% of the working population in Europe and the USA is engaged in shift-work that involves nightwork, which is most prevalent (above 30%) in the health-care, industrial manufactur ing, mining, transport, communication, leisure, and hospitality sectors. Among the many diff erent patterns of shiftwork, those including nightwork are the most disruptive for the circadian clock. Six of eight epidemiological studies from various geographical regions, most notably two independent cohort studies of nurses engaged in shiftwork at night, have noted a modestly increased risk of breast cancer in long-term employees compared with those who are not engaged in shiftwork at night. These studies are limited by potential confounding and inconsistent defi nitions of shiftwork, with several focused on a single profession. The incidence of breast cancer was also modestly increased in most cohorts of female fl ight attendants, who also experience circadian disruption by frequently crossing time zones. Limitations of studies in these fl ight attendants include the potential for detection bias, proxy measures of exposure, and potential uncontrolled confounding by reproductive factors and cosmic radiation. Several diff erent rodent models have been used to test the eff ect of disruption of the circadian system on tumour development. More than 20 studies investigated the eff ect of constant light, dim light at night, simulated chronic jet lag, or circadian timing of carcinogens, and most showed a major increase in tumour incidence. No clear eff ect was seen for light pulses at night or constant darkness. A similar number of studies investigated the eff ect of reduced nocturnal melatonin concentrations or removal of the pineal gland (where melatonin is produced) in tumour development and most showed increases in the incidence or growth of tumours. Exposure to light at night disturbs the circadian system with alterations of sleep-activity patterns, suppression of melatonin production, and de regul ation of circadian genes involved in cancer-related pathways. Inactivation of the circadian Period gene, Per2, promotes tumour develop ment in mice, and in human breast and endo metrial tumours, the expression of PERIOD genes is inhibited. In animals, melatonin suppression can lead to changes in the gonadotrophin axis. In humans, sleep deprivation and the ensuing melatonin suppression lead to immunodefi ciency. For example, sleep deprivation suppresses natural killer-cell activity and changes the T-helper 1/T-helper 2 cytokine balance, reducing cellular immune defence and surveillance. On the basis of “limited evidence in humans for the carcinogenicity of shift-work that involves nightwork”, and “suffi cient evidence in experimental animals for the carcinogenicity of light during the daily dark period (biological night)”, the Working Group concluded that “shift-work that involves circadian disruption is probably carcinogenic to humans” (Group 2A). Painters are potentially exposed to many chemicals used as pigments, extenders, binders, solvents, and additives. Painters can also be exposed to other workplace hazards, such as asbestos or crystalline silica. Cohort and linkage studies of painters have shown consistent and signifi cant increases in lung cancer compared with the general population. No information on tobacco smoking was available in the cohort studies; however, the increases are comparable to results from many case–control studies that controlled for smoking. A meta-analysis by the Working Group of all independent studies, including two recent large studies, showed a signifi cant excess risk of about 20% overall, and of 50% when the analysis was restricted to smoking-adjusted estimates from population-based case–control studies. Increased mortality from mesothelioma was consistently noted. Similarly, cohort and linkage studies showed consistent 20–25% increases in the occurrence of urinary bladder cancer in painters, and similar increases were noted in case– control studies that controlled for smoking. Although fi ndings for lymphatic and haemopoietic cancers in painters were inconsistent, four of fi ve case– control studies reported signifi cant increases in childhood leukaemia associated with maternal exposure to paint. The risks tended to be greater when mothers were exposed before or during, rather than after, pregnancy, and two studies showed some evidence of an increasing risk with increasing exposure. Upcoming meetings February 5–12, 2008 Industrial and cosmetic dyes and related exposures

In February, 2007, 26 scientists from 15 countries met at the International Agency for Research on Cancer (IARC) in Lyon, France, to reassess the carcino-genicity of alcoholic beverages and of ethyl carbamate (urethane), a frequent contaminant of fermented foods and beverages. These assessments will be published as volume 96 of the IARC Monographs.

In October, 2006, 19 scientists from eight countries met at the International Agency for Research on Cancer (IARC) in Lyon, France, to assess the carcinogenicity of household solid fuel combustion (coal and biomass) and of high-temperature frying. These assessments will be published as volume 95 of the IARC Monographs. About half of the world’s population, mostly in low-resource and mediumresource coun tries, use solid fuels for cooking or heating, often in poorly ventilated spaces. WHO identifi ed in door smoke from combustion of solid fuels as one of the top ten risks for worldwide burden of disease. Products of incomplete combustion contain respirable (coarse, fi ne, and ultrafi ne) particles and many volatile and nonvolatile organic compounds, including carcinogens such as benzo[a]pyrene, formaldehyde, and benzene. Average indoor concen trations of particulate matter (

In June, 2006, 19 scientists from eight countries met at the International Agency for Research on Cancer (IARC) in Lyon, France, to assess the carcinogenicity of ingested nitrate and nitrite, and the cyanobacterial peptide toxins microcystin-LR and nodularins. These agents are linked environmentally through the runoff of agricultural fertilisers that increase nitrogen concentrations in surface water and groundwater, and that could contribute to cyanobacterial growth in surface water. The assessments will be published as volume 94 of the IARC Monographs. Nitrate and nitrite are naturallyoccurring ions. In the past century, the global nitrogen cycle has been increasingly aff ected by nitrogen fi xation for agricultural activities, which now exceeds the amount that occurs naturally. Both groundwater and surface water can be contaminated by excess nitrate as a result of agricultural activities. Human exposure to nitrate and nitrite is mainly from the ingestion of food. Important sources include vegetables, cereal products, and cured meat. Drinking-water is generally not the main source of nitrate, unless concentrations exceed the WHO guideline of 50 mg/L, which is especially found in contaminated groundwater. Ingested nitrate (NO3) is excreted in the saliva and reduced to nitrite (NO 2) mainly by oral bacteria. Under acidic conditions in the stomach, nitrite then reacts readily with nitrosatable compounds, especially sec ondary amines and alkyl amides, to generate N-nitroso compounds. Several N-nitroso compounds are potential human carcinogens. The nitrosation reactions can be inhibited by the presence of vitamin C or other antioxidants. Some epidemiological studies assessed the risk of cancer in people who had high intake of nitrite or nitrate and low intake of vitamin C, a dietary pattern that could result in increased endogenous formation of N-nitroso compounds. The Working Group weighted these studies more heavily than studies without this information. From the epidemiological studies of nitrate in food, no increased risk of cancer was seen. For nitrate in drinkingwater, epidemiological studies were few, exposure levels were low, and endogenous nitrosation was not often considered. For ingested nitrite, the risk for stomach cancer was investigated in seven well-designed case-control studies. Six of these showed consistent, positive associations, four of which were signifi cant. Two studies looked at eff ect modifi cation, and the risk was most pronounced in people who had high nitrite and low vitamin C intake. Neither of the two cohort studies reported a clear positive association. No study accounted for potential confounding or eff ect modifi cation by Helicobacter pylori, an important risk factor for stomach cancer. For oesophageal cancer, two well-designed case-control studies investigated an association with nitrite intake. Both reported a positive association for nitrite intake overall; for people with high nitrite and low vitamin C intake, these associations were signifi cant. For brain tumours, two of fi ve casecontrol studies in children showed positive associations with nitrite intake. In one study, children born to mothers with the highest intake of nitrite from cured meat during pregnancy had a three-fold increased risk for brain tumours. The other study reported an increased risk for astroglial brain tumours in the children of mothers whose drinking-water had high nitrite concentrations. For adult brain cancer, no clear pattern emerged from seven case-control studies. The Working Group concluded that there is “limited evidence of carcinogenicity” for nitrite in food based on the association with stomach cancer. For nitrate in food and nitrate or nitrite in drinking-water, the studies provide “inadequate evidence of carcinogenicity”. No increased incidence of tumours was recorded in mice and rats if nitrate alone was added to the drinking-water or to the diet, providing inadequate evidence of carcinogenicity. Mice given nitrite in drinking-water showed a signifi cant trend in the incidence of forestomach papillomas and carcinomas combined. Rats exposed to nitrite in utero and throughout life had an increased incidence of lymphoreticular tumours, and mice with similar exposure had raised incidences of lymphoma and lung tumours. These results provide limited evidence of carcinogenicity for nitrite alone. Many studies of mice and rats tested nitrite in combination with specifi c secondary or tertiary amines or amides, added to the diet or drinkingwater, or by gastric intubation. Most combinations resulted in increased incidences of benign and malignant tumours at many organ sites. The Working Group concluded that these results provided “suffi cient evidence of carcinogenicity” for nitrite in combination with amines or amides. The combination of positive and negative results from epidemiological Upcoming meetings

(1996). Cancer Risk Assessment: Historical Perspectives, Current Issues, and Future Directions. Drug and Chemical Toxicology: Vol. 19, No. 3, pp. 161-185.

The IARC Monographs have been published continuously since 1971. For the 100th Vol. of the programme the evidence on all human carcinogens that have been identified to date has been updated. 147 experts from 28 countries contributed to the Vol. 100 series which was developed in six meetings from Oct 2008 to Oct 2009 (A. Pharmaceuticals, 23 agents; B. Biological agents, 11 agents; C. Metals, particles and fibres, 14 agents; D. Radiation, 14 agents; E. Lifestyle factors, 11 agents; F. Chemicals and related occupations, 34 agents). For each agent evaluations of the evidence in humans and in experimental animals and an overall evaluation of the human carcinogenicity have been developed and tumour sites with sufficient evidence of carcinogenicity as well as tumour sites that are strongly suspected and plausible mechanisms have been identified. All Group 1 carcinogens have been re-affirmed, several new Group 1 carcinogens and additional tumour sites for Group 1 carcinogens have been identified. Cancers of the colon, rectum and ovaries (mucinous type) have been added to the long list of tobacco smoking-related cancers, and parental smoking causes hepatoblastoma in the offspring and probably childhood leukemia. Acetaldehyde associated with alcohol consumption is carcinogenic to humans and causes cancers of the oesophagus, and head and neck. Based on sufficient evidence in humans for cutaneous and ocular melanoma, use of UV emitting tanning devices is now classified as “carcinogenic to humans”. In addition to lung cancer and mesothelioma, asbestos has now been linked with cancers of the larynx and ovaries, and leather dust has been identified as causing cancers of the nasal cavity and paranasal sinuses. There is now sufficient epidemiological evidence for TCDD exposure and all cancers combined, making TCDD the first agent classified initially in Group 1 based on sufficient animal data and mechanisms, to be later confirmed by increased cancer incidence in humans. Like TCDD, 2,3,4,7,8-pentachlordibenzofuran and 3,3’,4,4’, 5-pentachlorobiphenyl are complete carcinogens in experimental animals, and there is extensive evidence that they act through the same AhR-mediated mechanism. The Working Group classified these two chemicals in Group 1. The Working Group unanimously reaffirmed the classification of formaldehyde in Group 1, based on sufficient evidence in humans of nasopharyngeal cancer and concluded that, overall, there is sufficient evidence for leukaemia, particularly myeloid leukaemia. The re-affirmation of all group 1 carcinogens underlines the robust procedures and criteria for human carcinogen identification employed in the IARC Monographs Programme. Two additional Working Groups will be convened to develop scientific publications that build on the data that have been summarized in Volume 100: 1) Tumour-site concordance between humans and experimental animals; 2) Mechanisms involved in human carcinogenesis. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 869.