world cancer report - iarc

COLORECTAL CANCER
SUMMARY
> Cancers of the colon and rectum are
rare in developing countries, but are the
second most frequent malignancy in
affluent societies; over 940,000 cases
occur annually worldwide.
> A major etiological factor is lifestyle
involving a diet rich in fat, refined carbohydrates
and animal protein, combined
with low physical activity.
>Studies suggest that risk can be reduced
by decreasing meat consumption and
increasing intake of vegetables and fruit.
>Sequential genetic alterations mediate
development of colon cancer, the earliest
such change being mutation of the
APC gene.
>Familial clustering has usually a genetic
basis. Typical syndromes include familial
adenomatosis polyposis (FAP) and
hereditary non-polyposis colon cancer
(HNPCC).
> Colonoscopy is the most reliable means
for early detection. Progressively
improved treatment has resulted in a
five-year survival rate of about 50%.
Definition
The majority of cancers occurring in the
colon and rectum are adenocarcinomas,
which account for more than 90% of all
large bowel tumours.
Epidemiology
Colorectal cancer ranks second in terms
of both incidence and mortality in more
developed countries. Nearly 945,000 new
colorectal cancer cases are diagnosed
worldwide each year and colorectal cancer
is responsible for some 492,000
deaths. There is significant geographical
variation in age-standardized incidence as
well as in cumulative 0-74 year incidence,
198 Human cancers by organ site
Fig. 5.29 Global incidence of colorectal cancer in women. Incidence rates are highest in North America,
Western Europe and Australia/New Zealand.
high rates occurring in countries of
Europe, North America, in Australia and,
more recently, in Japan (Fig. 5.29, Table
5.4). Migrant groups rapidly reach the
higher level of risk of the adopted country,
indicating that environmental factors play
an important role in etiology. In North
America, the trend towards increased incidence
is now reversed [1] and a possible
beneficial influence of dietary change
and/or endoscopic polypectomy has been
suggested. In Western Europe, this recent
downward trend has not yet been
observed. Most cases occur after the age
of 60, except in individuals who carry a
genetic predisposition.
Etiology
Colorectal cancer most commonly
occurs sporadically and is inherited in
only 5% of cases. Diet is by far the most
important exogenous factor so far identified
in the etiology of colorectal cancer
[2]. It has been estimated that 70% of
colorectal cancers could be prevented by
nutritional intervention; various promot-
< 3.8 < 7.7 < 12 < 21.2
Age-standardized incidence/100,000 population
< 43.4
ing and protective factors have been
identified in cohort and case-control
studies [3]. There is convincing evidence
that a diet high in calories and rich in animal
fats, most often as red meat, and
Cumulative
incidence (%)
Country Male Female
Black, USA 5.60 4.22
White, USA 4.98 3.38
Denmark 4.48 3.53
Netherlands 4.25 3.25
Osaka, Japan 4.03 2.28
Qidong China 1.13 0.29
Khon Kaen,Thailand 1.06 0.64
Table 5.4 Cumulative incidence of colorectal cancer.
The sum of incidence rates for all ages 0-74
provides a measure of the risk of developing colorectal
cancer over a life span, in the absence of
any other cause of death.