News
www.thelancet.com/oncology Vol 10 August 2009 751
Special Report: Policy
A review of human carcinogens—Part D: radiation
In June 2009, 20 scientists from nine
countries met at the International
Agency for Research on Cancer (IARC)
to reassess the carcinogenicity of the
types of radiation previously classifi ed
as “carcinogenic to humans” (Group 1)
and to identify additional tumour sites
and mechanisms of carcinogenesis
(table and panel). These assessments
will be published as part D of Volume
100 of the IARC Monographs.
1

Alpha particles, consisting of two
protons and two neutrons, are a
densely ionising type of radiation
with low capacity to penetrate living
tissue (less than 0·1 mm). Beta
particles are electrons or positrons
that are less ionising, but more
penetrating (up to a few milimetres).
The health hazards resulting from
radionuclides that emit these
particles largely occur after internal
deposition. Epidemiological evidence
shows a number of radionuclides that
emit alpha or beta particles increase
cancer risks at several anatomical sites
(table). The Working Group reaffi rmed
the carcinogenicity of internally
deposited radionuclides that emit
alpha or beta particles (Group 1).
After the Chernobyl accident, a
sharp increase in the risk of thyroid
cancer was found with exposure to
radioiodines, particularly iodine-131,
during childhood and adolescence.
2,3

This increased risk might be due to
higher milk intake per unit of body
weight among children; a higher thyroid
dose per unit of iodine-131 intake from
milk; a higher susceptibility per unit of
thyroid dose; or a combination of these.
Radon exposure occurs mainly
through contamination of indoor
air by radon released from soil and
building materials. Combined analyses
of case–control studies now estimate
that residential exposure to radon gas
is the leading cause of lung cancer after
tobacco smoke (8–15% attributable
risk in Europe and North America).
4,5

X-rays and gamma-rays are
sparsely ionising electromagnetic
radiation that penetrate living tissue,
typically producing fast electrons that
deposit energy, resulting in tissue
damage. Extensive study of atomic-
bomb survivors shows increased
cancer risks at multiple anatomical
sites.
6
Current evidence adds to the
list of tumours caused by x-rays
and gamma-rays (table), and also
establishes that in-utero exposure
increases the risk of cancer at multiple
sites.
7,8
The Working Group reaffi rmed
the carcinogenicity of x-radiation and
gamma-radiation (Group 1).
Neutrons are produced by nuclear
reactions and are a main component
of cosmic radiation. They are highly
penetrating and interact with
the traversed tissue, producing
protons, other charged particles, and
gamma-radiation. Epidemiological
evidence is inadequate to assess the
carcinogenicity of neutrons, because
of co-exposures to other types of
radiation. However, the evidence
of cancer in experimental animals
is suffi cient, and mechanistic data
show that neutrons transfer their
energy in clusters of ionising events—
resulting in similar, but more severe,
local damage than that induced by
x-rays or gamma-rays. On the basis
of this evidence, the Working Group
reaffi rmed the carcinogenicity of
neutron radiation (Group 1).
Each type of ionising radiation
(panel) transfers energy in the
form of highly structured tracks of
Upcoming meetings
Sept 29–Oct 6, 2009
Lifestyle Factors
Oct 20–27, 2009
Chemical Agents and Related
Occupations
http://monographs.iarc.fr/
Radiation type Major study populations Tumour sites (and types) on which suffi cient evidence is based
Alpha-particle and beta-particle emitters
Radon-222 and decay products General population (residential exposure), underground miners Lung
Radium-224 and decay products Medical patients Bone
Radium-226, radium-228, and decay products Radium-dial painters Bone, paranasal sinus and mastoid process (radium-226 only)
Thorium-232 and decay products Medical patients Liver, extrahepatic bile ducts, gall bladder, leukaemia (excluding CLL)
Plutonium Plutonium-production workers Lung, liver, bone
Phosphorus-32 Medical patients Acute leukaemia
Fission products, including strontium-90 General population, following nuclear reactor accident Solid cancers, leukaemia
Radioiodines, including iodine-131 Children and adolescents, following nuclear reactor accident Thyroid
X-radiation or gamma-radiation Atomic-bomb survivors, medical patients; in-utero exposure (off spring
of pregnant medical patients and of atomic-bomb survivors)
Salivary gland, oesophagus, stomach, colon, lung, bone, skin (BCC),
female breast, urinary bladder, brain and CNS, leukaemia (excluding CLL),
thyroid, kidney (atomic-bomb survivors, medical patients); multiple sites
(in-utero exposure)
Solar radiation General population Skin (BCC, SCC, melanoma)
UV-emitting tanning devices General population Skin (melanoma), eye (melanoma, particularly choroid and ciliary body)
CLL=chronic lymphocytic leukaemia. BCC=basal-cell carcinoma. SCC=squamous-cell carcinoma.
Table: Radiation exposures with suffi cient evidence in humans