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  1. 1. MODELLO GENERALE (National Academy of Science, USA, 1986) VALUTAZIONE DEL RISCHIO GESTIONE DEL RISCHIOIdentificazione delfattore di rischio Valutazione delle(L’agente causa un danno conseguenze economiche,per la salute?) sociali, politiche e sulla salute pubblicaDefinizione della dose – Caratterizzazionerisposta del rischio(Qual è la relazione tra (Qual è l’incidenza edose e risposta?) l’entità del danno Sviluppo di opzioni per la salute?) normativeValutazione dellaesposizione(Quali esposizioni sono Limitidimostrate o prevedibili indiverse condizioni?)
  2. 2. monographs/index.php IARC Publications•WHO/IARC Classification of Tumours•IARC Working Group Reports•IARC Handbooks of Cancer Prevention•IARC Monographs on the Evaluation of Carcinogen•IARC Scientific Publications Series
  3. 3. (a) Exposure dataData are summarized, as appropriate, on the basis ofelements such as production, use, occurrence andexposure levels in the workplace and environmentand measurements in human tissues and body fluids.Quantitative data and time trends are given tocompare exposures in different occupations andenvironmental settings. Exposure to biological agentsis described in terms of transmission, prevalence andpersistence of infection.
  4. 4. (b) Cancer in humansResults of epidemiological studies pertinent to anassessment of human carcinogenicity aresummarized. When relevant, case reports andcorrelation studies are also summarized. The targetorgan(s) or tissue(s) in which an increase in cancerwas observed is identified. Dose-response and otherquantitative data may be summarized when available
  5. 5. (c) Cancer in experimental animalsData relevant to an evaluation of carcinogenicity inanimals are summarized. For each animal species,study design and route of administration, it is statedwhether an increased incidence, reduced latency, orincreased severity or multiplicity of neoplasms orpreneoplastic lesions were observed, and the tumoursites are indicated. If the agent produced tumoursafter prenatal exposure or in single-doseexperiments, this is also mentioned. Negativefindings, inverse relationships, dose-response andother quantitative data are also summarized.•.
  6. 6. (d) Mechanistic and other relevant dataData relevant to the toxicokinetics (absorption,distribution, metabolism, elimination) and thepossible mechanism(s) of carcinogenesis (e.g.genetic toxicity, epigenetic effects) are summarized.In addition, information on susceptible individuals,populations and life-stages is summarized. Thissection also reports on other toxic effects, includingreproductive and developmental effects, as well asadditional relevant data that are considered to beimportant.
  7. 7. (d) Mechanistic and other relevant dataMechanistic and other relevant data may provide evidence ofcarcinogenicity and also help in assessing the relevance andimportance of findings of cancer in animals and in humans.The nature of the mechanistic and other relevant data dependson the biological activity of the agent being considered. TheWorking Group considers representative studies to give aconcise description of the relevant data and issues that theyconsider to be important; thus, not every available study iscited. Relevant topics may include toxicokinetics, mechanismsof carcinogenesis, susceptible individuals, populations and life-stages, other relevant data and other adverse effects. Whendata on biomarkers are informative about the mechanisms ofcarcinogenesis, they are included in this section.
  8. 8. B. SCIENTIFIC REVIEW AND EVALUATION 2. Studies of cancer in humans• (b) Quality of studies consideredIt is necessary to take into account the possible roles of bias, confounding and chance in the interpretation of epidemiological studies. Bias is the effect of factors in study design or execution that lead erroneously to a stronger or weaker association than in fact exists between an agent and disease. Confounding is a form of bias that occurs when the relationship with disease is made to appear stronger or weaker than it truly is as a result of an association between the apparent causal factor and another factor that is associated with either an increase or decrease in the incidence of the disease. The role of chance is related to biological variability and the influence of sample size on the precision of estimates of effect.
  9. 9. B. SCIENTIFIC REVIEW AND EVALUATION 2. Studies of cancer in humans• f) Criteria for causalityAfter the quality of individual epidemiological studies of cancer has been summarized and assessed, a judgement is made concerning the strength of evidence that the agent in question is carcinogenic to humans. In making its judgement, the Working Group considers several criteria for causality (Hill, 1965).A strong association (e.g. a large relative risk) is more likely to indicate causality than a weak association, although it is recognized that estimates of effect of small magnitude do not imply lack of causality and may be important if the disease or exposure is common.
  10. 10. B. SCIENTIFIC REVIEW AND EVALUATION 2. Studies of cancer in humans• f) Criteria for causalityAssociations that are replicated in several studies of the same design or that use different epidemiological approaches or under different circumstances of exposure are more likely to represent a causal relationship than isolated observations from single studies. If there are inconsistent results among investigations, possible reasons are sought (such as differences in exposure), and results of studies that are judged to be of high quality are given more weight than those of studies that are judged to be methodologically less sound.
  11. 11. B. SCIENTIFIC REVIEW AND EVALUATION 2. Studies of cancer in humans• f) Criteria for causalityIf the risk increases with the exposure, this is considered to be a strong indication of causality, although the absence of a graded response is not necessarily evidence against a causal relationship. The demonstration of a decline in risk after cessation of or reduction in exposure in individuals or in whole populations also supports a causal interpretation of the findings.
  12. 12. B. SCIENTIFIC REVIEW AND EVALUATION 2. Studies of cancer in humans• f) Criteria for causalityA number of scenarios may increase confidence in a causal relationship. On the one hand, an agent may be specific in causing tumours at one site or of one morphological type. On the other, carcinogenicity may be evident through the causation of multiple tumour types.Temporality, precision of estimates of effect, biological plausibility and coherence of the overall database are considered. Data on biomarkers may be employed in an assessment of the biological plausibility of epidemiological observations.
  13. 13. IARC categories of carcinogenesis, for humans studies1. The sufficient category is identical to the causal criteriadefined earlier, i.e., strength of association, dose-response,consistency, biological plausibility, temporal cogency,control of confounding and bias, specificity, andcoherence.
  14. 14. IARC categories of carcinogenesis, for humans studies2. The limited category is used when “a positiveassociation has been observed between exposure to theagent, mixture or exposure circumstance and cancer forwhich a causal interpretation is considered to be credible,but change, bias or confounding could not be ruled outwith reasonable confidence”.
  15. 15. IARC categories of carcinogenesis, for humans studies3. The inadequate category is used when “the availablestudies are of insufficient quality, consistency or statisticalpower to permit a conclusion regarding the presence orabsence of a causal association, or no data on cancer onhumans are available.
  16. 16. IARC categories of carcinogenesis, for humans studies4. The lack of evidence category is used when “there areseveral adequate studies … which are mutually consistentin not showing a positive association between exposure tothe agent, mixture or exposure circumstance and anystudied cancer or at any observed level of exposure …“Lack of carcinogenicity’ is inevitably limited to thecancer sites, conditions and levels of exposure and lengthof observation covered by the available studies. Inaddition, the possibility of a very small risk at the levels ofexposure studied can never be excluded”.
  17. 17. IARC categories of carcinogenesis, for animal studies1. Sufficient evidence exists when “a causal relationshiphas been established between the agent or mixture and anincreased incidence of malignant neoplasm … in (a) twoor more species of animals or (b) in two or moreindependent studies in one species carried out at differenttimes or in different laboratories or under differentprotocols.”.
  18. 18. IARC categories of carcinogenesis, for animal studies2. Limited evidence exists when there are “data [that]suggest a carcinogenic effect but are limited for making adefinitive evaluation because (a) the evidence ofcarcinogenicity is restricted to a single experiment; or (b)there are unresolved questions regarding … dosing,conduct or interpretation of the study; or (c) the agent ormixture increases the incidence only of benign neoplasm… or of certain neoplasm which mat occur spontaneouslyin high incidence in certain strains [of animals]”.
  19. 19. IARC categories of carcinogenesis, for animal studies3. Inadequate evidence exists when there are “studies[that] cannot be interpreted as showing either thepresence or absence of a carcinogenic effect because ofmajor qualitative or quantitative limitations, or no data oncancer in experimental animal are available.”
  20. 20. IARC categories of carcinogenesis, for animal studies4. Lack of carcinogenicity exists when there are“adequate studies involving at least two species areavailable which show that … the agent or mixture is notcarcinogenic…”
  21. 21. IARC Classification Scheme for Human and Animal Evidence of Carcinogenesis Animal EvidenceHuman Evidence Sufficient Limited Inadequated (-) CarcinogenicitySufficient Group 1 Group 1 Group 1 Group 1Limited Group 2A Group 2B Group 2B Group 2BInadequated Group 2B Group 3 Group 3 Group 3(-) Carcinogenicity Group 2B Group 4 Group 4 Group 4
  22. 22. Criteria for Lung Cancer Causation for Silica Exposure and for Silicosis Between First and Second IARC Reports Silica-Exposed Silica-Exposed Workers with Workers with Point of Evidence Workers, Workers, Silicosis Silicosis IARC 1986 IARC 1997 IARC 1986 IARC 1997 Strong relative risk ± * *** *** Dose-response gradient ± ** ± ** Consistent finding * ** *** *** Controlled confounding ± * ± * Biological plausibility * ** ± * Temporal cogency ** ** ** ** Specificity ** ** ** ** Overall coherence * ** *** ***Note: * = criteria met; ** = more than minimal criteria met; *** = large body of evidence; ± = incomplete evidence.
  23. 23. Evidenze e valutazione finale Animale Suff Lim Inad Suff 1 1 1UO Lim 2A 2B 2BMO (1*) Inad 2B 3 3 (2A*,3*) (2B*)
  24. 24. La Classificazione IARC degli agenti, delle misture e delle esposizioni ( 1 Cancerogeno accertato per l’uomo: vi è sufficiente evidenza di cancerogenicità nell’uomo in studi epidemiologici adeguati.Gruppo 2 2A probabile cancerogeno per l’uomo, sulla base di evidenza limitata nell’uomo ed evidenza sufficiente in animali da esperimento. 2B possibile cancerogeno per l’uomo, sulla base di evidenza limitata nell’uomo e evidenzia non del tutto sufficiente negli animali da esperimento oppure di evidenza sufficiente negli animali ed evidenza inadeguata nell’uomo.Gruppo 3 Non classificati per cancerogenicità sull’uomo (tutto ciò che non rientra nei precedenti viene posto in questo gruppo).Gruppo 4 Probabilmente non cancerogeno per l’uomo: assenza di cancerogenicità nell’uomo e negli animali da esperimento; in presenza di un ampio numero di dati sperimentali