The objective of the programme is to prepare, with the
help of international Working Groups of experts, and to
publish in the form of Monographs, critical reviews
and evaluations of evidence on the carcinogenicity of
a wide range of human exposures. The Monographs
represent the first step in carcinogen risk assessment,
which involves examination of all relevant information
in order to assess the strength of the available evidence
that an agent could alter the age-specific incidence of
cancer in humans. The Monographs may also indicate
where additional research efforts are needed, specifically
when data immediately relevant to an evaluation are not
available.
In this Preamble, the term 'agent' refers to any entity
or circumstance that is subject to evaluation in a Monograph.
As the scope of the programme has broadened, categories
of agents now include specific chemicals, groups of related
chemicals, complex mixtures, occupational or environmental
exposures, cultural or behavioural practices, biological
organisms and physical agents. This list of categories
may expand as causation of, and susceptibility to, malignant
disease become more fully understood.
A cancer 'hazard' is an agent that is capable of causing
cancer under some circumstances, while a cancer 'risk'
is an estimate of the carcinogenic effects expected from
exposure to a cancer hazard. The Monographs are
an exercise in evaluating cancer hazards, despite the
historical presence of the word 'risks' in the title.
The distinction between hazard and risk is important,
and the Monographs identify cancer hazards even
when risks are very low at current exposure levels, because
new uses or unforeseen exposures could engender risks
that are significantly higher.
In the Monographs, an agent is termed 'carcinogenic'
if it is capable of increasing the incidence of malignant
neoplasms, reducing their latency, or increasing their
severity or multiplicity. The induction of benign neoplasms
may in some circumstances (see Part
B, Section 3a) contribute to the judgement that the
agent is carcinogenic. The terms 'neoplasm' and 'tumour'
are used interchangeably.
The Preamble continues the previous usage of the phrase
'strength of evidence' as a matter of historical continuity,
although it should be understood that Monographs
evaluations consider studies that support a finding of
a cancer hazard as well as studies that do not.
Some epidemiological and experimental studies indicate
that different agents may act at different stages in the
carcinogenic process, and several different mechanisms
may be involved. The aim of the Monographs has
been, from their inception, to evaluate evidence of carcinogenicity
at any stage in the carcinogenesis process, independently
of the underlying mechanisms. Information on mechanisms
may, however, be used in making the overall evaluation
(IARC, 1991; Vainio et al., 1992; IARC, 2005, 2006;
see also Part B, Sections
4 and 6).
As mechanisms of carcinogenesis are elucidated, IARC convenes
international scientific conferences to determine whether
a broad-based consensus has emerged on how specific mechanistic
data can be used in an evaluation of human carcinogenicity.
The results of such conferences are reported in IARC Scientific
Publications, which, as long as they still reflect the
current state of scientific knowledge, may guide subsequent
Working Groups.
Although the Monographs have emphasized hazard
identification, important issues may also involve dose-response
assessment. In many cases, the same epidemiological and
experimental studies used to evaluate a cancer hazard
can also be used to estimate a dose-response relationship.
A Monograph may undertake to estimate dose-response
relationships within the range of the available epidemiological
data, or it may compare the dose-response information
from experimental and epidemiological studies. In some
cases, a subsequent publication may be prepared by a separate
Working Group with expertise in quantitative dose-response
assessment.
The Monographs are used by national and international
authorities to make risk assessments, formulate decisions
concerning preventive measures, provide effective cancer
control programmes and decide among alternative options
for public health decisions. The evaluations of IARC Working
Groups are scientific, qualitative judgements on the evidence
for or against carcinogenicity provided by the available
data. These evaluations represent only one part of the
body of information on which public health decisions may
be based. Public health options vary from one situation
to another and from country to country and relate to many
factors, including different socioeconomic and national
priorities. Therefore, no recommendation is given with
regard to regulation or legislation, which are the responsibility
of individual governments or other international organizations.
Posted 23 January 2006
