Classification schemes for carcinogenicity based on hazard-identification have become outmoded and serve neither science nor society

A UK framework for the assessment and integration of different scientific evidence streams in chemical risk assessment

BACKGROUND

Few methods are available for transparently combining different evidence streams for chemical risk assessment to reach an integrated conclusion on the probability of causation. Hence, the UK Committees on Toxicity (COT) and on Carcinogenicity (COC) have reviewed current practice and developed guidance on how to achieve this in a transparent manner, using graphical visualisation.

METHODS/APPROACH

All lines of evidence, including toxicological, epidemiological, new approach methodologies, and mode of action should be considered, taking account of their strengths/weaknesses in their relative weighting towards a conclusion on the probability of causation. A qualitative estimate of the probability of causation is plotted for each line of evidence and a combined estimate provided.

DISCUSSION/CONCLUSIONS

Guidance is provided on integration of multiple lines of evidence for causation, based on current best practice. Qualitative estimates of probability for each line of evidence are plotted graphically. This ensures a deliberative, consensus conclusion on likelihood of causation is reached. It also ensures clear communication of the influence of the different lines of evidence on the overall conclusion on causality. Issues on which advice from the respective Committees is sought varies considerably, hence the guidance is designed to be sufficiently flexible to meet this need.

Towards a future regulatory framework for chemicals in the European Union - Chemicals 2.0

The body of EU chemicals legislation has evolved since the 1960s, producing the largest knowledge base on chemicals worldwide. Like any evolving system, however, it has become increasingly diverse and complex, resulting in inefficiencies and potential inconsistencies. In the light of the EU Chemicals Strategy for Sustainability, it is therefore timely and reasonable to consider how aspects of the system could be simplified and streamlined, without losing the hard-earned benefits to human health and the environment. In this commentary, we propose a conceptual framework that could be the basis of Chemicals 2.0 - a future safety assessment and management approach that is based on the application of New Approach Methodologies (NAMs), mechanistic reasoning and cost-benefit considerations. Chemicals 2.0 is designed to be a more efficient and more effective approach for assessing chemicals, and to comply with the EU goal to completely replace animal testing, in line with Directive 2010/63/EU. We propose five design criteria for Chemicals 2.0 to define what the future system should achieve. The approach is centered on a classification matrix in which NAMs for toxicodynamics and toxicokinetics are used to classify chemicals according to their level of concern. An important principle is the need to ensure an equivalent, or higher, protection level.

A new approach methodology using kinetically-derived maximum dose levels in risk assessment - A case study with afidopyropen

We present a case study for afidopyropen (AF; insecticide) to characterize chronic dietary human health risk using a Risk 21-based approach. Our objective is to use a well-tested pesticidal active ingredient (AF) to show how a new approach methodology (NAM), using the kinetically-derived maximum dose (KMD) and with far less animal testing, can reliably identify a health-protective point of departure (PoD) for chronic dietary human health risk assessments (HHRA). Chronic dietary HHRA involves evaluation of both hazard and exposure information to characterize risk. Although both are important, emphasis has been placed on a checklist of required toxicological studies for hazard characterization, with human exposure information only considered after evaluation of hazard data. Most required studies are not used to define the human endpoint for HHRA. The information presented demonstrates a NAM that uses the KMD determined by saturation of a metabolic pathway, which can be used as an alternative POD. In these cases, the full toxicological database may not need to be generated. Demonstration that the compound is not genotoxic and that the KMD is protective of adverse effects in 90-day oral rat and reproductive/developmental studies is sufficient to support the use of the KMD as an alternative POD.

A new approach to the classification of carcinogenicity

Concern over substances that may cause cancer has led to various classification schemes to recognize carcinogenic threats and provide a basis to manage those threats. The least useful schemes have a binary choice that declares a substance carcinogenic or not. This overly simplistic approach ignores the complexity of cancer causation by considering neither how the substance causes cancer, nor the potency of that mode of action. Consequently, substances are classified simply as "carcinogenic", compromising the opportunity to properly manage these kinds of substances. It will likely be very difficult, if not impossible, to incorporate New Approach Methodologies (NAMs) into binary schemes. In this paper we propose a new approach cancer classification scheme that segregates substances by both mode of action and potency into three categories and, as a consequence, provides useful guidance in the regulation and management of substances with carcinogenic potential. Examples are given, including aflatoxin (category A), trichlorethylene (category B), and titanium dioxide (category C), which demonstrate the clear differentiation among these substances that generate appropriate levels of concern and management options.

Rethinking chronic toxicity and carcinogenicity assessment for agrochemicals project (ReCAAP): A reporting framework to support a weight of evidence safety assessment without long-term rodent bioassays

Rodent cancer bioassays have been long-required studies for regulatory assessment of human cancer hazard and risk. These studies use hundreds of animals, are resource intensive, and certain aspects of these studies have limited human relevance. The past 10 years have seen an exponential growth of new technologies with the potential to effectively evaluate human cancer hazard and risk while reducing, refining, or replacing animal use. To streamline and facilitate uptake of new technologies, a workgroup comprised of scientists from government, academia, non-governmental organizations, and industry stakeholders developed a framework for waiver rationales of rodent cancer bioassays for consideration in agrochemical safety assessment. The workgroup used an iterative approach, incorporating regulatory agency feedback, and identifying critical information to be considered in a risk assessment-based weight of evidence determination of the need for rodent cancer bioassays. The reporting framework described herein was developed to support a chronic toxicity and carcinogenicity study waiver rationale, which includes information on use pattern(s), exposure scenario(s), pesticidal mode-of-action, physicochemical properties, metabolism, toxicokinetics, toxicological data including mechanistic data, and chemical read-across from similar registered pesticides. The framework could also be applied to endpoints other than chronic toxicity and carcinogenicity, and for chemicals other than agrochemicals.

[Important Points at Interpretation ofNongenotoxic-Carcinogenicity Induced by Pesticidesin Rodent Bioassays]

Assessment of carcinogenicity is important for human health at dietary risk assessment of pesticide residues. This article indicated important points on interpretation of carcinogenicity in toxicological evaluation of pesticide residues based on principles of risk analysis in foods by CODEX to be a guide for risk assessors. This guidance was referred from the guidance on carcinogenicity evaluation by international and/or national organizations, and the interpretations of Food Safety Commissions of Japan (FSCJ) published in their risk assessment reports. We focused on carcinogenicity obtained from routine carcinogenicity bioassays in rodents. The guidance includes the purpose and usefulness of the bioassay studies, consideration points to be carcinogenicity and influencing factors to carcinogenicity in the test to judge carcinogenic hazard at hazard identification. Considering on human relevance as carcinogenic hazard also was proposed using practical case examples. Next, a carcinogenic hazard is evaluated on dose-response relationship to judge points of departure on carcinogenicity. At the end of this article, we challenged our recommendation on future assessment of carcinogenicity to progress from hazard to risk.

Reflections on chemical risk assessment or how (not) to serve society with science

In this paper, we want to shed light on the demand for chemical and toxicological data growing ever more faster than science can supply and other aspects of assessing chemical risks, including the demand for 'ever greater safety'. The treatise that follows is on the one hand rooted in well-established toxicological theory and on the other hand utilises emerging toxicological insights. Both theoretical conceptions and empirical substantiations are discussed to build up a perspective that produces an outlook on innovation and proliferates insights into our inexorable and invaluable exposure to 'the chemical'. We propose that in toxicology, with the implicit mandatory linear routine of dose-response, there is no tangible scientific drive to understand and unearth the actual empirical dose-response curve for chemicals under scrutiny. This can and should be improved upon as to advance the science of toxicology and to optimise current and future regulatory efforts.

The codification of hazard and its impact on the hazard versus risk controversy

The long running controversy about the relative merits of hazard-based versus risk-based approaches has been investigated. There are three levels of hazard codification: level 1 divides chemicals into dichotomous bands of hazardous and non-hazardous; level 2 divides chemicals into bands of hazard based on severity and/or potency; and level 3 places each chemical on a continuum of hazard based on severity and/or potency. Any system which imposes compartments onto a continuum will give rise to issues at the boundaries, especially with only two compartments. Level 1 schemes are only justifiable if there is no variation in severity, or potency or if there is no threshold. This is the assumption implicit in GHS/EU classification for carcinogenicity, reproductive toxicity and mutagenicity. However, this assumption has been challenged. Codification level 2 hazard assessments offer a range of choices and reduce the built-in conflict inherent in the level 1 process. Level 3 assessments allow a full range of choices between the extremes and reduce the built-in conflict even more. The underlying reason for the controversy between hazard and risk is the use of level 1 hazard codification schemes in situations where there are ranges of severity and potency which require the use of level 2 or level 3 hazard codification. There is not a major difference between level 2 and level 3 codification, and they can both be used to select appropriate risk management options. Existing level 1 codification schemes should be reviewed and developed into level 2 schemes where appropriate.

The modification of cancer risk by chemicals

Advances in understanding of the process of carcinogenesis have undermined the concept of chemicals being classifiable as either carcinogens or non-carcinogens. Elements of carcinogenesis are happening all the time and a proportion of cancers cannot be prevented, the 'bad luck hypothesis'. Although the proportion that can be prevented is disputed, it is important to continue efforts to reduce it. Factors that increase cancer risk have been grouped into intrinsic factors that cannot be modified, and endogenous and exogenous factors that can be modified. Chemicals are exogenous factors that can be modified by risk management measures. Chemicals can alter three key rates that influence cancer risk: cell division, mutation rate per cell division, transformation rate of mutated cells to cancer. These rates can form the basis of a dynamic cancer risk model, a generic, adverse outcome pathway for carcinogenesis where chemicals are considered for their ability to modify cancer risk rather than simply whether they are classed as carcinogens or non-carcinogens. This allows the development of different strategies for assessing cancer risk that use a range of data sources and are not dependent on using long-term bioassays and epidemiology to identify carcinogens. The framework will also allow difficult questions such as the effect of less than lifetime exposures and the effect of exposures to more than one chemical to be addressed.

Knowledge About Gastrointestinal Cancers in People Referred for Endoscopy and Colonoscopy During a Screening Program: a Cross-sectional Study in Guilan, North of Iran

PURPOSE

The most northern and northwestern regions of Iran are at a high risk for gastrointestinal cancers. In this study, we evaluated knowledge of gastrointestinal (GI) cancers in people referred for endoscopy and colonoscopy screening.

METHODS

This cross-sectional study was carried out among 461 people who were under the patronage of a local relief foundation and referred for endoscopy and colonoscopy to the Gastrointestinal and Liver Disease Research Center (GLDRC), Rasht, north of Iran, from March 2016 to March 2017. A well-defined two-sectioned questionnaire was carried out for each group.

RESULTS

Overall, 300 and 161 individuals were in the gastric and colon cancer knowledge group, respectively. The level of knowledge in various areas of gastric and colon cancer was desirable. In general, the average of different domains in gastric and colon cancer knowledge questions were 20.2 ± 6.6 and 19.2 ± 4.9, with the knowledge level higher than the mean in gastric cancer (58%) and colon cancer (67.1%). The mean score of knowledge of GI cancers in terms of risk factor indicated a significant relationship between BMI and alcohol consumption. Meanwhile, a meaningful relationship between symptoms and BMI with knowledge was declared. About domains of colon cancer, there was a significant relationship between younger age and knowledge in the risk factor.

CONCLUSIONS

The results of this study can provide an opportunity to formulate strategies to achieve goals, especially in the field of education, prevention, and control of the disease by raising knowledge for the general public and educating people who are responsible for providing and delivering health services to this community.

Lack of potential carcinogenicity for steviol glycosides - Systematic evaluation and integration of mechanistic data into the totality of evidence

Steviol glycosides are present in the leaves of the Stevia rebaudiana plant, have a sweet taste, and have been used as a sweetener for centuries. To build on previous authoritative safety assessments of steviol glycosides, a systematic assessment of mechanistic data related to key characteristics of carcinogens (KCCs) was conducted. Over 900 KCC-relevant endpoints from peer-reviewed literature and high-throughput screening data (ToxCast/Tox21) were identified across individual steviol glycosides and derivatives, metabolites, and whole leaf extracts. Most data (both in vivo and in vitro, including human cells), showed inactivity. Studies were weighted according to quality and relevance. Although data were available for eight of the ten KCC, genotoxicity, oxidative stress, inflammation, and cell proliferation/cell death represent the KCCs with the most data. The data for these KCC primarily show beneficial activity (anti-inflammatory, antioxidant, and anti-proliferative). Following integration across all data, and accounting for study quality and relevance, the totality of the evidence demonstrated an overall lack of genotoxic and carcinogenic activity for steviol glycosides. This is in agreement with previous regulatory decisions, and is consistent with the lack of tumor response in two-year rodent cancer bioassays. The findings support prior conclusions that steviol glycosides are unlikely to be carcinogenic in humans.

Weight of evidence analysis of the tumorigenic potential of 1,3-dichloropropene supports a threshold-based risk assessment

1,3-Dichloropropene (1,3-D; CAS #542-75-6) is a fumigant used for preplant treatment of soil to control parasitic nematodes and manage soil borne diseases for numerous fruit, vegetable, field and tree and vine crops across diverse global agricultural areas. In the USA, 1,3-D has historically been classified by the U.S. EPA as likely to be carcinogenic to humans via both oral and inhalation routes. This classification for the oral route was primarily based upon increases in multiple tumor types observed in National Toxicology Program (NTP) cancer bioassays in rats and mice, while the classification for the inhalation route was based upon increased benign bronchioloalveolar adenomas in a mouse study conducted by The Dow Chemical Company. Based on U.S. EPA standard risk assessment methodologies, a low-dose linear extrapolation approach has been used to estimate risks to humans. Furthermore, genotoxicity associated with 1,3-D was historically considered a potential mode of action (MOA) for its tumorigenicity. New information is available and additional studies have been conducted that reveal a different picture of the tumorigenic potential of 1,3-D. These data and information include: (1) initial cancer studies by the NTP were conducted on an antiquated form of 1,3-D which contained a known mutagen/carcinogen, epichlorohydrin, as a stabilizer while current 1,3-D fumigants use epoxidized soybean oil (ESO) as the stabilizer; (2) results from two additional oral rodent cancer bioassays conducted on the modern form of 1,3-D became available and these two studies reveal a lack of carcinogenicity; (3) a newly conducted Big Blue study in F344 rats via the oral route further confirms that 1,3-D is not an in vivo genotoxicant; and (4) a newly conducted repeat dose inhalation toxicokinetic (TK) study shows that linear dose proportionality is observed below 30 ppm, which demonstrates the non-relevance of 60 ppm 1,3-D-induced benign lung tumors in mice for human health assessment. This weight of evidence review is organized as follows: (a) the TK of 1,3-D are presented because of relevant considerations when evaluating test doses/concentrations and reported findings of tumorigenicity; (b) the genotoxicity profile of 1,3-D is presented, including a contemporary study in order to put a possible genotoxicity MOA into perspective; (c) the six available bioassays are reviewed followed by (d) scientifically supported points of departure (PODs) and evaluation of human exposure for use in risk assessment. Through this assessment, all available data support the conclusion that 1,3-D is not a tumorigen at doses below 12.5 mg/kg bw/day via the oral route or at doses below 30 ppm via the inhalation route. These findings and clearly identified PODs show that a linear low dose extrapolation approach is not appropriate and a threshold-based risk assessment for 1,3-D is human health protective. Finally, in 2019, the Cancer Assessment Review Committee (CARC) reevaluated the carcinogenic potential of 1,3-D. In accordance with the EPA's Final Guidelines for Carcinogen Risk Assessment, the CARC classified 1,3-D (Telone) as "Suggestive Evidence of Carcinogenic Potential based on the presence of liver tumors by the oral route in male rats only." Given this finding, EPA stated that "quantification of human cancer risk is not required. The CARC recommends using a non-linear approach (i.e. reference dose (RfD)) that will adequately account for all chronic toxicity including carcinogenicity, that could result from exposure to 1,3-dichloropropene."

Evaluation of the carcinogenicity of dichloromethane in rats, mice, hamsters and humans

Dichloromethane (DCM) is a high production volume chemical (>1000 t/a) mainly used as an industrial solvent. Carcinogenicity studies in rats, mice and hamsters have demonstrated a malignant tumor inducing potential of DCM only in the mouse (lung and liver) at 1000-4000 ppm whereas human data do not support a conclusion of cancer risk. Based on this, DCM has been classified as a cat. 2 carcinogen. Dose-dependent toxicokinetics of DCM suggest that DCM is a threshold carcinogen in mice, initiating carcinogenicity via the low affinity/high capacity GSTT1 pathway; a biotransformation pathway that becomes relevant only at high exposure concentrations. Rats and hamsters have very low activities of this DCM-metabolizing GST and humans have even lower activities of this enzyme. Based on the induction of specific tumors selectively in the mouse, the dose- and species-specific toxicokinetics in this species, and the absence of a malignant tumor response by DCM in rats and hamsters having a closer relationship to DCM toxicokinetics in humans and thus being a more relevant animal model, the current classification of DCM as human carcinogen cat. 2 remains appropriate.

A retrospective study on EU harmonised classifications for carcinogenicity to guide future research

Under European Regulation (EC) No 1272/2008 on the classification, labelling and packaging of substances and mixtures (CLP), chemicals can be classified as carcinogenic if they are considered to induce tumours, increase tumour incidence and/or malignancy, or shorten the time to tumour occurrence. Cancer classifications are divided into different hazard categories: Carc. 1A (known human carcinogen), Carc. 1B (presumed human carcinogen), Carc. 2 (suspected human carcinogen), and chemicals not classified for carcinogenicity. Selecting which classification is appropriate can be challenging, as judgements need to be made both on the existing hazard data and on its relevance to humans. One aspect to be considered in defining human relevance is a chemical's mode of action (MoA); the series of necessary key events that lead from an exposure to the adverse effect (in this case, tumours). This work aims to identify and discuss some of the features that have led ECHA's Committee for Risk Assessment (RAC) to decide upon harmonised cancer classifications for chemicals, and to prioritise future research on MoA and/or human relevance. RAC bases its decisions on cancer classification on both the weight-of-evidence (WoE) and strength-of-evidence (SoE) of this particular activity. Multiple factors contribute, including the species in which tumours are seen, and the relevance of the MoA to human health.

Chemistry, safety, and regulatory considerations in the use of nitrite and nitrate from natural origin in meat products - Invited review

Nitrite and nitrate have been traditionally used for the preservation of meat products because of the effective antimicrobial action of nitrite against Clostridium botulinum, the outgrowth of its spores as well as other bacteria. However, the use of nitrite and nitrate has been questioned in last half century due to the possible generation of N-nitrosamines through reaction of nitrite with secondary amines. Nitrite replacement strategies began in the 70s addressing these issues and instigated searches for natural alternatives to nitrate and nitrite, or for natural sources of nitrite and nitrate such as vegetable extracts. These alternatives have been considered by producers and consumers as an attractive practice even though they may also have some risks. This manuscript reviews and discusses the chemistry, safety, and regulatory considerations in the use of nitrite and nitrate from natural origin for the preservation of meat products.

Chemical carcinogen safety testing: OECD expert group international consensus on the development of an integrated approach for the testing and assessment of chemical non-genotoxic carcinogens

While regulatory requirements for carcinogenicity testing of chemicals vary according to product sector and regulatory jurisdiction, the standard approach starts with a battery of genotoxicity tests (which include mutagenicity assays). If any of the in vivo genotoxicity tests are positive, a lifetime rodent cancer bioassay may be requested, but under most chemical regulations (except plant protection, biocides, pharmaceuticals), this is rare. The decision to conduct further testing based on genotoxicity test outcomes creates a regulatory gap for the identification of non-genotoxic carcinogens (NGTxC). With the objective of addressing this gap, in 2016, the Organization of Economic Cooperation and Development (OECD) established an expert group to develop an integrated approach to the testing and assessment (IATA) of NGTxC. Through that work, a definition of NGTxC in a regulatory context was agreed. Using the adverse outcome pathway (AOP) concept, various cancer models were developed, and overarching mechanisms and modes of action were identified. After further refining and structuring with respect to the common hallmarks of cancer and knowing that NGTxC act through a large variety of specific mechanisms, with cell proliferation commonly being a unifying element, it became evident that a panel of tests covering multiple biological traits will be needed to populate the IATA. Consequently, in addition to literature and database investigation, the OECD opened a call for relevant assays in 2018 to receive suggestions. Here, we report on the definition of NGTxC, on the development of the overarching NGTxC IATA, and on the development of ranking parameters to evaluate the assays. Ultimately the intent is to select the best scoring assays for integration in an NGTxC IATA to better identify carcinogens and reduce public health hazards.

How the 62-year old Delaney Clause continues to thwart science: Case study of the flavor substance β-myrcene

The Delaney Clause is a provision of the 1958 Food Additive Amendment to the Food, Drug and Cosmetic Act of 1938 which stipulates that if a substance is found by the Food and Drug Administration to be carcinogenic in any species of animal or in humans, then it cannot be used as a food additive. This paper presents a case study of β-myrcene, one of seven synthetic substances that was challenged under the Delaney Clause, ultimately resulting in revocation of its regulatory approval as a food additive despite a lack of safety concern. While it is listed as a synthetic flavor in 21 CFR 172.515, β-myrcene is also a substance naturally occurring in a number of dietary plants. The exposure level to naturally-occurring β-myrcene is orders of magnitude higher (estimated to be 16,500 times greater) than the exposure via β-myrcene added to food as a flavoring substance. The National Toxicology Program conducted genotoxicity testing (negative), a 13-week range-finding study, and a two-year cancer bioassay in B6C3F1 mice and F344/N rats. An increase in liver tumors was seen in male mice and kidney tumors in male rats, ultimately resulting in β-myrcene being classified by IARC as a Class 2B carcinogen and being listed on California Proposition 65; in contrast, β-myrcene is not classified as a carcinogen by any other regulatory authority. The doses administered in the NTP bioassay were five-six orders of magnitude higher than human exposures, and the FDA concluded after a thorough evaluation that there was no safety concern associated with the use of β-myrcene as a flavor substance at the current use level. The Delaney Clause, however, does not consider the exposure potential or the human health relevance of effects observed in animals. The lack of options available to the US FDA led to the 2018 decision to remove β-myrcene from the list of approved food additives. This revocation has contributed to the ongoing erosion of trust in regulatory agencies (and industry), which has both economic implications for food manufacturers and consumers alike, and implications for consumer perception of safety of the US food supply. It is time for us to reconsider the rationale behind any legislation that relies on classification alone, and whether there is, in fact, a reason to still classify nongenotoxic carcinogens at all.

Toxic Responses Induced at High Doses May Affect Benchmark Doses

To derive reference points (RPs) for health-based guidance values, the benchmark dose (BMD) approach increasingly replaces the no-observed-adverse-effect level approach. In the BMD approach, the RP corresponds to the benchmark dose lower confidence bounds (BMDLs) of a mathematical dose-response model derived from responses of animals over the entire dose range applied. The use of the entire dose range is seen as an important advantage of the BMD approach. This assumes that responses over the entire dose range are relevant for modeling low-dose responses, the basis for the RP. However, if part of the high-dose response was unnoticed triggered by a mechanism of action (MOA) that does not work at low doses, the high-dose response distorts the modeling of low-dose responses. Hence, we investigated the effect of high-dose specific responses on BMDLs by assuming a low- and a high-dose MOA. The BMDLs resulting from modeling fictitious quantal data were scattered over a broad dose range overlapping with the toxic range. Hence, BMDLs are sensitive to high-dose responses even though they might be irrelevant to low-dose response modeling. When applying the BMD approach, care should be taken that high-dose specific responses do not unduly affect the BMDL that derives from low doses.

The safety evaluation of food flavoring substances: the role of genotoxicity studies

The Flavor and Extract Manufacturers Association (FEMA) Expert Panel relies on the weight of evidence from all available data in the safety evaluation of flavoring substances. This process includes data from genotoxicity studies designed to assess the potential of a chemical agent to react with DNA or otherwise cause changes to DNA, either in vitro or in vivo. The Panel has reviewed a large number of in vitro and in vivo genotoxicity studies during the course of its ongoing safety evaluations of flavorings. The adherence of genotoxicity studies to standardized protocols and guidelines, the biological relevance of the results from those studies, and the human relevance of these studies are all important considerations in assessing whether the results raise specific concerns for genotoxic potential. The Panel evaluates genotoxicity studies not only for evidence of genotoxicity hazard, but also for the probability of risk to the consumer in the context of exposure from their use as flavoring substances. The majority of flavoring substances have given no indication of genotoxic potential in studies evaluated by the FEMA Expert Panel. Examples illustrating the assessment of genotoxicity data for flavoring substances and the consideration of the factors noted above are provided. The weight of evidence approach adopted by the FEMA Expert Panel leads to a rational assessment of risk associated with consumer intake of flavoring substances under the conditions of use.

Recommendations for further revisions to improve the International Agency for Research on Cancer (IARC) Monograph program

In 2019, the International Agency for Research on Cancer (IARC) "Preamble to the IARC Monographs" expanded guidance regarding the scientific approaches that should be employed in its monographs. These amendments to the monograph development process are an improvement but still fall short in several areas. While the revised Preamble lays out broad methods and approaches to evaluate scientific evidence, there is a lack of specificity with regard to how IARC Working Groups will conduct consistent evaluations in a standardized, objective, and transparent manner; document systematic review and evidence integration actions, and substantiate how these actions and decisions inform the ultimate classifications. Furthermore, no guidance is provided to ensure Working Groups consistently incorporate mechanistic evidence in a robust manner using a defined approach in the context of 21st century knowledge of modes of action. Nor are the conclusions of the working groups subjected to outside, independent scientific peer review. Continued improvements and modernization of the procedures for evaluating, presenting, and communicating study quality, and in the methods used to conduct and peer-review evidence-based decision making will benefit the Working Group members, the IARC Monographs Programme overall, and the international regulatory community and public who rely upon the monographs.

Hazard identification, classification, and risk assessment of carcinogens: too much or too little? - Report of an ECETOC workshop

The European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) organized a workshop "Hazard Identification, Classification and Risk Assessment of Carcinogens: Too Much or Too Little?" to explore the scientific limitations of the current binary carcinogenicity classification scheme that classifies substances as either carcinogenic or not. Classification is often based upon the rodent 2-year bioassay, which has scientific limitations and is not necessary to predict whether substances are likely human carcinogens. By contrast, tiered testing strategies founded on new approach methodologies (NAMs) followed by subchronic toxicity testing, as necessary, are useful to determine if a substance is likely carcinogenic, by which mode-of-action effects would occur and, for non-genotoxic carcinogens, the dose levels below which the key events leading to carcinogenicity are not affected. Importantly, the objective is not for NAMs to mimic high-dose effects recorded in vivo, as these are not relevant to human risk assessment. Carcinogenicity testing at the "maximum tolerated dose" does not reflect human exposure conditions, but causes major disturbances of homeostasis, which are very unlikely to occur at relevant human exposure levels. The evaluation of findings should consider biological relevance and not just statistical significance. Using this approach, safe exposures to non-genotoxic substances can be established.

The use of adverse outcome pathways in the safety evaluation of food additives

In the last decade, adverse outcome pathways have been introduced in the fields of toxicology and risk assessment of chemicals as pragmatic tools with broad application potential. While their use in the pharmaceutical and cosmetics sectors has been well documented, their application in the food area remains largely unexplored. In this respect, an expert group of the International Life Sciences Institute Europe has recently explored the use of adverse outcome pathways in the safety evaluation of food additives. A key activity was the organization of a workshop, gathering delegates from the regulatory, industrial and academic areas, to discuss the potentials and challenges related to the application of adverse outcome pathways in the safety assessment of food additives. The present paper describes the outcome of this workshop followed by a number of critical considerations and perspectives defined by the International Life Sciences Institute Europe expert group.

N-phosphonomethylglycine utilization by the psychrotolerant yeast Solicoccozyma terricola M 3.1.4

Solicoccozyma terricola M 3.1.4., the yeast strain isolated from soil sample from blueberry cultivation in Miedzyrzec Podlaski in Poland, is capable to split of phosphorus to nitrogen and nitrogen to carbon bonds in N-phosphonomethylglycine (PMG, glyphosate). The biodegradation process proceeds in the phosphate-independent manner. It is the first example of a psychrotolerant yeast strain able to degrade PMG via CN bond cleavage accompanied by AMPA formation and not like in most microorganisms via CP bond disruption followed by the sarcosine pathway. Glyphosate oxidoreductase (GOX) type activity was detected in cell-free extracts prepared from S. terricola M 3.1.4. pregrown on 4 mM PMG as a sole phosphorus and nitrogen source in cultivation medium.

Lack of potential carcinogenicity for sucralose - Systematic evaluation and integration of mechanistic data into the totality of the evidence

Sucralose is widely used as a sugar substitute. Many studies and authoritative reviews have concluded that sucralose is non-carcinogenic, based primarily on animal cancer bioassays and genotoxicity data. To add to the body of knowledge on the potential carcinogenicity of sucralose, a systematic assessment of mechanistic data was conducted. This entailed using a framework developed for the quantitative integration of data related to the proposed key characteristics of carcinogens (KCCs). Data from peer-reviewed literature and the ToxCast/Tox21 database were evaluated using an algorithm that weights data for quality and relevance. The resulting integration demonstrated an overall lack of activity for sucralose across the KCCs, with no "strong" activity observed for any KCC. Almost all data collected demonstrated inactivity, including those conducted in human models. The overall lack of activity in mechanistic data is consistent with findings from animal cancer bioassays. The few instances of activity across the KCC were generally accompanied by limitations in study design in the context of either quality and/or dose and model relevance, highlighted upon integration of the totality of the evidence. The findings from this comprehensive and integrative evaluation of mechanistic data support prior conclusions that sucralose is unlikely to be carcinogenic in humans.

One science-driven approach for the regulatory implementation of alternative methods: A multi-sector perspective

EU regulations call for the use of alternative methods to animal testing. During the last decade, an increasing number of alternative approaches have been formally adopted. In parallel, new 3Rs-relevant technologies and mechanistic approaches have increasingly contributed to hazard identification and risk assessment evolution. In this changing landscape, an EPAA meeting reviewed the challenges that different industry sectors face in the implementation of alternative methods following a science-driven approach. Although clear progress was acknowledged in animal testing reduction and refinement thanks to an integration of scientifically robust approaches, the following challenges were identified: i) further characterization of toxicity pathways; ii) development of assays covering current scientific gaps, iii) better characterization of links between in vitro readouts and outcome in the target species; iv) better definition of alternative method applicability domains, and v) appropriate implementation of the available approaches. For areas having regulatory adopted alternative methods (e.g., vaccine batch testing), harmonised acceptance across geographical regions was considered critical for broader application. Overall, the main constraints to the application of non-animal alternatives are the still existing gaps in scientific knowledge and technological limitations. The science-driven identification of most appropriate methods is key for furthering a multi-sectorial decrease in animal testing.

Prioritization of reproductive toxicants in unconventional oil and gas operations using a multi-country regulatory data-driven hazard assessment

BACKGROUND

Recent trends have witnessed the global growth of unconventional oil and gas (UOG) production. Epidemiologic studies have suggested associations between proximity to UOG operations with increased adverse birth outcomes and cancer, though specific potential etiologic agents have not yet been identified. To perform effective risk assessment of chemicals used in UOG production, the first step of hazard identification followed by prioritization specifically for reproductive toxicity, carcinogenicity and mutagenicity is crucial in an evidence-based risk assessment approach. To date, there is no single hazard classification list based on the United Nations Globally Harmonized System (GHS), with countries applying the GHS standards to generate their own chemical hazard classification lists. A current challenge for chemical prioritization, particularly for a multi-national industry, is inconsistent hazard classification which may result in misjudgment of the potential public health risks. We present a novel approach for hazard identification followed by prioritization of reproductive toxicants found in UOG operations using publicly available regulatory databases.

METHODS

GHS classification for reproductive toxicity of 157 UOG-related chemicals identified as potential reproductive or developmental toxicants in a previous publication was assessed using eleven governmental regulatory agency databases. If there was discordance in classifications across agencies, the most stringent classification was assigned. Chemicals in the category of known or presumed human reproductive toxicants were further evaluated for carcinogenicity and germ cell mutagenicity based on government classifications. A scoring system was utilized to assign numerical values for reproductive health, cancer and germ cell mutation hazard endpoints. Using a Cytoscape analysis, both qualitative and quantitative results were presented visually to readily identify high priority UOG chemicals with evidence of multiple adverse effects.

RESULTS

We observed substantial inconsistencies in classification among the 11 databases. By adopting the most stringent classification within and across countries, 43 chemicals were classified as known or presumed human reproductive toxicants (GHS Category 1), while 31 chemicals were classified as suspected human reproductive toxicants (GHS Category 2). The 43 reproductive toxicants were further subjected to analysis for carcinogenic and mutagenic properties. Calculated hazard scores and Cytoscape visualization yielded several high priority chemicals including potassium dichromate, cadmium, benzene and ethylene oxide.

CONCLUSIONS

Our findings reveal diverging GHS classification outcomes for UOG chemicals across regulatory agencies. Adoption of the most stringent classification with application of hazard scores provides a useful approach to prioritize reproductive toxicants in UOG and other industries for exposure assessments and selection of safer alternatives.

Exposure to permethrin and cancer risk: a systematic review

No systematic reviews are available on data from humans on cancer risk from exposure to permethrin, a widely used insecticide for which some animal studies have reported positive findings based on mechanisms that may not be relevant to humans. We identified potentially relevant articles through a search of electronic databases which included all studies of pesticide exposure and human cancer. A total of 18 articles were selected, including six identified from the list of references of other articles. Most articles were based on analyzes of the Agriculture Health Study (AHS); they provided no evidence of an increased risk of cancers of colon, rectum, pancreas, lung, melanoma, female breast, prostate, urinary bladder, as well as non-Hodgkin lymphoma (including its main subtypes), and leukemia. An increased risk of multiple myeloma was reported among AHS members with the highest tertile of estimated permethrin exposure (odds ratio 5.01; 95% confidence interval 2.41-10.42; p for trend <0.01). A subsequent analysis with a larger number of cases found a less pronounced association between permethrin exposure and risk of multiple myeloma; no exposed cases were reported in a separate study. Two case-control studies of childhood leukemia reported an association with biological markers of permethrin metabolites; in another study self-reported exposure to permethrin was associated with risk in children below 1 year of age, but not in older children. In conclusion, permethrin exposure does not seem to entail a risk of cancer in humans. Results on multiple myeloma and childhood leukemia are weak and inconsistent, and require replication in independent populations.

What is the meaning of 'A compound is carcinogenic'?

Chemical Carcinogens are compounds which can cause cancer in humans and experimental animals. This property is attributed to many chemicals in the public discussion, resulting in a widespread perception of danger and threat. In contrast, a scientific analysis of the wide and non-critical use of the term 'carcinogenic' is warranted. First, it has to be clarified if the compound acts in a genotoxic or non-genotoxic manner. In the latter case, an ineffective (safe) threshold dose without cancer risk can be assumed. In addition, it needs to be investigated if the mode-of-action causing tumors in laboratory animals is relevant at all for humans. In case the compound is clearly directly genotoxic, an ineffective threshold dose cannot be assumed. However, also in this case it is evident that high doses of the compound are generally associated with a high cancer risk, low doses with a lower one. Based on dose-response data from animal experiments, quantification of the cancer risk is carried out by mathematical modeling. If the safety margin between the lowest carcinogenic dose in animals and the relevant level of exposure in humans exceeds 10,000, the degree of concern is classified as low. Cases, where the compound turns out to be genotoxic in one study or one test only but not in others or only in vitro but not in vivo, are particularly difficult to explain and cause controversial discussions. Also for indirectly genotoxic agents, an ineffective (threshold) dose must be assumed. The situation is aggravated by the use of doubtful epidemiological studies in humans such as in the case of glyphosate, where data from mixed exposure to various chemicals were used. If such considerations are mixed with pure hazard classifications such as 'probably carcinogenic in humans' ignoring dose-response behavior and mode-of-action, the misinformation and public confusion are complete. It appears more urgent but also more difficult than ever to return to a scientifically based perception of these issues.

Human relevance of rodent liver tumors: Key insights from a Toxicology Forum workshop on nongenotoxic modes of action

The Toxicology Forum sponsored a workshop in October 2016, on the human relevance of rodent liver tumors occurring via nongenotoxic modes of action (MOAs). The workshop focused on two nuclear receptor-mediated MOAs (Constitutive Androstane Receptor (CAR) and Peroxisome Proliferator Activated Receptor-alpha (PPARα), and on cytotoxicity. The goal of the meeting was to review the state of the science to (1) identify areas of consensus and differences, data gaps and research needs; (2) identify reasons for inconsistencies in current regulatory positions; and (3) consider what data are needed to demonstrate a specific MOA, and when additional research is needed to rule out alternative possibilities. Implications for quantitative risk assessment approaches were discussed, as were implications of not considering MOA and dose in hazard characterization and labeling schemes. Most, but not all, participants considered the CAR and PPARα MOAs as not relevant to humans based on quantitative and qualitative differences. In contrast, cytotoxicity is clearly relevant to humans, but a threshold applies. Questions remain for all three MOAs concerning what data are necessary to determine the MOA and to what extent it is necessary to exclude other MOAs.

How well can carcinogenicity be predicted by high throughput "characteristics of carcinogens" mechanistic data?

IARC has begun using ToxCast/Tox21 data in efforts to represent key characteristics of carcinogens to organize and weigh mechanistic evidence in cancer hazard determinations and this implicit inference approach also is being considered by USEPA. To determine how well ToxCast/Tox21 data can explicitly predict cancer hazard, this approach was evaluated with statistical analyses and machine learning prediction algorithms. Substances USEPA previously classified as having cancer hazard potential were designated as positives and substances not posing a carcinogenic hazard were designated as negatives. Then ToxCast/Tox21 data were analyzed both with and without adjusting for the cytotoxicity burst effect commonly observed in such assays. Using the same assignments as IARC of ToxCast/Tox21 assays to the seven key characteristics of carcinogens, the ability to predict cancer hazard for each key characteristic, alone or in combination, was found to be no better than chance. Hence, we have little scientific confidence in IARC's inference models derived from current ToxCast/Tox21 assays for key characteristics to predict cancer. This finding supports the need for a more rigorous mode-of-action pathway-based framework to organize, evaluate, and integrate mechanistic evidence with animal toxicity, epidemiological investigations, and knowledge of exposure and dosimetry to evaluate potential carcinogenic hazards and risks to humans.

Use of genetic toxicity data in GHS mutagenicity classification and labeling of substances

One of the key outcomes of testing the potential genotoxicity or mutagenicity of a substance is the conclusion on whether the substance should be classified as a germ cell mutagen and the significance of this for other endpoints such as carcinogenicity. The basis for this conclusion are the criteria presented in classification and labelling systems such as the Globally Harmonized System for classification and labeling (GHS). This article reviews the classification criteria for germ cell mutagenicity and carcinogenicity and how they are applied to substances with evidence of mutagenicity. The implications and suitability of such a classification for hazard communication, risk assessment, and risk management are discussed. It is proposed that genotoxicity assessments should not focus on specifically identifying germ cell mutagens, particularly given the challenges associated with communicating this information in a meaningful way. Rather the focus should be on deriving data to characterize the mode of action and for use in the risk assessment of mutagens, which could then feed into a more robust, risk based management of mutagenic substances versus the current more hazard based approaches. Environ. Mol. Mutagen. 58:354-360, 2017. © 2017 Wiley Periodicals, Inc.

IARC use of oxidative stress as key mode of action characteristic for facilitating cancer classification: Glyphosate case example illustrating a lack of robustness in interpretative implementation

The International Agency for Research on Cancer (IARC) has formulated 10 key characteristics of human carcinogens to incorporate mechanistic data into cancer hazard classifications. The analysis used glyphosate as a case example to examine the robustness of IARC's determination of oxidative stress as "strong" evidence supporting a plausible cancer mechanism in humans. The IARC analysis primarily relied on 14 human/mammalian studies; 19 non-mammalian studies were uninformative of human cancer given the broad spectrum of test species and extensive use of formulations and aquatic testing. The mammalian studies had substantial experimental limitations for informing cancer mechanism including use of: single doses and time points; cytotoxic/toxic test doses; tissues not identified as potential cancer targets; glyphosate formulations or mixtures; technically limited oxidative stress biomarkers. The doses were many orders of magnitude higher than human exposures determined in human biomonitoring studies. The glyphosate case example reveals that the IARC evaluation fell substantially short of "strong" supporting evidence of oxidative stress as a plausible human cancer mechanism, and suggests that other IARC monographs relying on the 10 key characteristics approach should be similarly examined for a lack of robust data integration fundamental to reasonable mode of action evaluations.