world cancer report - iarc

Fig. 2.30 Correlation between regional incidence of hepatocellular carcinoma, dietary exposure to aflatoxin
B 1, and prevalence of G>T mutations at codon 249 of the p53 tumour suppressor gene.
Polychlorinated dibenzo-para-dioxins
(which include 2,3,7,8-tetrachlorodibenzopara-dioxin,
TCDD) are ubiquitous pollutants
in soil sediments and air
(Environmental pollution, p39). Human
exposure occurs through eating meat and
related foods. The burden of cancer attributable
to such exposure is unknown [9].
Chemicals generated during food
preparation
Some chemicals formed during food
preparation may present a carcinogenic
hazard. The toxicity of these chemicals
generally warrants the adoption of means
to minimize their formation, particularly
during industrialized food preparation. It
has not been possible to attribute cancer
causation in humans to hazards of this
type specifically.
A possible pragmatic approach to the prioritization
of chemical carcinogens occurring
as food contaminants has been proposed.
The highest priority category is
chemical carcinogens that are believed to
act by a genotoxic mechanism [10].
46 The causes of cancer
p53
Heterocyclic amines
Certain heterocyclic amines are formed
by pyrolysis of two amino acids, creatine
and creatinine, during cooking of meat
and fish at high temperature. Heterocyclic
amines are carcinogenic in various
organs of mice, rats and non-human primates,
although their carcinogenic potential
in humans has not yet been established
[11]. Metabolism of heterocyclic
amines can vary between individuals due
to various genetic polymorphisms.
Polycyclic aromatic hydrocarbons
Polycyclic aromatic hydrocarbons can be
generated in meat when it is fried, roasted
or cooked over an open flame, and
many members of this chemical class
are carcinogenic. These compounds can
also be formed during the curing and
processing of raw foods prior to cooking.
A number of polycyclic aromatic hydrocarbons,
such as benzo[a]pyrene and
benzanthracene, are present in smoke
from the burning of fuels, tobacco and
weeds.
Fig. 2.31 Nitrosamines are present in smoked
fish consumed in many parts of the world, including
the Gambia.
N-Nitroso compounds
N-Nitroso compounds are a wide class of
chemicals, many of which (particularly
N-nitrosamines) are potent carcinogens in
several species of experimental animals,
and probably in humans [12]. Nitrosamines
may be formed by chemical reactions in
foods containing added nitrates and
nitrites, such as salt-preserved fish and
meat, and in foods processed by smoking
or direct fire drying. The use of fertilizers
may influence the level of nitrites in food,
which may be a factor in determining generation
of nitrosamines during food preparation
and storage. Some industrial procedures,
including brewing of beer, have
been modified to reduce nitrosamine formation.
Studies on volunteers consuming
supplements of nitrate, or large portions of
red meat, indicate that N-nitroso compounds
can also be produced endogenously
in the stomach and colon.
Endogenous formation of nitrosamines is
inhibited by several natural antioxidants,
such as vitamins C and E, present in fruit
and vegetables.
Metals
The hazard presented by dietary metals,
whether regarded as essential nutrients or
contaminants, is difficult to assess [13].