world cancer report - iarc

Fig. 4.42 The FOBT test for colorectal cancer (shown here is a Hemoccult II ® test). Three consecutive
stools samples are applied to the test card. After addition of the reaction solution, a blue coloration indicates
the presence of blood. A single positive result among the three samples indicates the need for a
clinical examination of the colon.
per year per life saved), screening for
colorectal cancer in the USA has been
evaluated as being below an arbitrary
financial threshold adopted in screening
(US$ 40,000 per year of life gained) and
in this regard compares favourably with
protocols for breast or cervical cancer
screening. It has been estimated that
screening 200,000 people in Australia
using the FOBT would detect 250
colorectal cancers and prevent as many
as 55 deaths. The FOBT gives the most
cost-effective programme, but prevents
fewer deaths than other programmes. A
single colonoscopy has a greater impact
on cancer mortality. Some health authorities
in developed countries acknowledge
the legitimacy of a screening protocol for
colorectal cancer. However, the high cost
of a generalized intervention and the limited
acceptance of the tests by the population
explain its limited application. It
has been shown that nurses can perform
sigmoidoscopy as competently as doctors,
as indicated by the duration of the
procedure, the ability to detect neoplasia
and the risk of complications. When a
lesion is detected in these circumstances,
a colonoscopy is performed by a
specialist.
Evidence of outcome
FOBT has been assessed in randomized
trials. An American trial [2] was based on
an annual rehydrated FOBT in volunteers.
The compliance was high (90.2%) and
38% of individuals screened underwent
colonoscopy. There was a 33% reduction
in specific mortality in the screened
group (Table 4.17). Reduction in cancer
incidence also occurred. In the two
European, population-based, randomized
trials [3,4] conducted in the UK and in
Denmark with a biennial non-rehydrated
FOBT, the compliance was lower (around
60%), only 4% of individuals tested had
colonoscopy and the reduction in mortality
was less (15%).
Screening by sigmoidoscopy has been
evaluated in case-control studies. In the
Kaiser study [13], rigid sigmoidoscopy was
associated with a 59% reduction in mortality
from cancer of the rectum and distal
colon. Scandinavian trials have shown less
compliance and a higher yield of detection
with sigmoidoscopy than with the FOBT. A
Screening protocols
Annual faecal occult blood test
Biennial faecal occult blood test
Annual faecal occult blood test
+ fibrosigmoidoscopy every 5 years
Fibrosigmoidoscopy every 5 years
Colonoscopy every 10 years
Colonoscopy once in a lifetime
Table 4.16 Options for population-based screening
protocols for colorectal cancer (in males and
females, from the age of 50 years).
cohort study in the USA has shown that
screening by endoscopy reduces mortality
from colorectal cancer by 50% and incidence
by 40% [8]. Primary endoscopic
screening is increasingly favoured as compared
to the FOBT protocol [9].
There is indirect evidence that primary
colonoscopy may reduce cancer mortality.
The National Polyp Study in the USA has
shown a 75% reduction in the risk of
colorectal cancer after polypectomy
[10,11]. Among persons of average risk,
above age 50, screening by colonoscopy
reveals cancer in 0-2.2% and large adenomas
in 3-11%. The number of colonoscopies
needed to detect one cancer in
screening is estimated at 143 for individuals
of either sex, aged at least 50, and 64
for males aged at least 60 years. The number
of colonoscopies needed to detect one
cancer in patients with a positive FOBT is
Screened annually Unscreened
Number of people 15,550 15,394
Number of colorectal cancers detected 323 356
Number of deaths from colorectal cancer 82 121
Mortality ratio 0.67 1.00
(deaths in screened/deaths in unscreened)
Table 4.17 The efficacy of screening by FOBT as reflected by the reduced mortality due to colorectal
cancers diagnosed in the group subject to annual screening in comparison with the unscreened group.
Screening for colorectal cancer
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