world cancer report - iarc

THYROID CANCER
SUMMARY
> Cancer of the thyroid gland is relatively
rare, but incidence is increasing in most
developed countries. About 120,000
cases occur annually.
> Apart from ionizing radiation, environmental
causes have not been well characterized.
In Eastern Europe (Belarus,
Ukraine, Russia), several hundred children
developed thyroid cancer following
the Chernobyl accident.
> Prognosis is usually good (around 90%
five-year survival for some tumour
types), even when lymph node metastases
are present.
Definition
Most thyroid cancers are well-differentiated
malignancies, which are predominantly
papillary (80-85%), and to a lesser extent,
follicular (10-15%) and Hürthle cell carcinomas
(3-5%). Anaplastic carcinoma and
medullary carcinoma are rare.
Epidemiology
Carcinoma of the thyroid gland is an
uncommon cancer although it is the most
common malignancy of the endocrine system
(Fig. 5.135). Generally, thyroid cancer
accounts for approximately 1% of total
cancer cases in developed countries.
There are about 122,000 new cases per
year worldwide.
Incidence of this disease is particularly
high in Iceland and Hawaii, where the rate
is nearly twice that in North European
countries, Canada and USA. In Hawaii, the
incidence rate of thyroid cancer in all ethnic
groups is higher than in the same ethnic
group living in their country of origin
and is particularly high among Chinese
males and Filipino females. Thyroid
tumours are rare in children, less than one
< 2.1 < 2.9 < 3.4
Fig. 5.135 Global differences in the incidence of thyroid cancer in women.
case per million per year in most developed
countries; the age-specific incidence
rates increase rapidly with age (Fig.
5.137). In the past three decades, incidence
rates have been increasing in most
developed countries, while mortality rates
have been slowly decreasing. In the year
2000, the annual mortality rate per
100,000 people was 0.3 for men and 0.6
for women [1]. Thyroid cancer causes
some 26,000 deaths every year.
Etiology
An association between thyroid cancer
and exposure to ionizing radiation was
already suggested in 1950 [2]. Many studies
have documented the increased risk of
papillary or follicular thyroid carcinoma in
individuals exposed to X- and γ-rays [3].
The risk of radiation-induced cancer is
considerably greater in those exposed as
young children than as adults. Before the
Chernobyl accident, epidemiological studies
appeared to indicate that radioactive
iodines were much less carcinogenic than
external X- or γ- irradiation. This is not
< 4.4
Age-standardized incidence/100,000 population
< 23.2
confirmed by the study of persons
exposed as children to fall-out from the
Chernobyl accident in the most contaminated
territories in Belarus, Ukraine and
Russia, where a dramatic increase in thyroid
cancer incidence attributable to
radioactive iodines has been observed.
Iodine deficiency is thought to be involved
in the development of thyroid cancer
because thyroid cancer incidence rates
Fig. 5.136 The Chernobyl nuclear power plant following
the 1986 accident. A marked increase in
the incidence of thyroid cancer in children has
been observed in areas exposed to radioactive
iodine.
Thyroid cancer
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