Report in English with a Dutch summary (KCE reports 45A)

KCE reports vol.45 Screening for Colorectal Cancer 39
(differences in commitment and in resources), and to the fact that the
acceptability of undergoing a colonoscopy turned out to be lower than
predicted.
Others studies are population-based prospective cohort studies137-139 or
retrospective population studies140-142, 123, 143.
To determine to what extent individuals with various family histories of
colorectal cancer are at risk a prospective, observational study of high risk
families, followed up over 16 years, was carried out in a tertiary referral family
cancer clinic in London 139. 1.678 individuals from families registered with the
cancer clinic were classified according to the strength of their family history:
HNPCC (if they fulfilled the Amsterdam criteria 144, 58), and one, two, or three
affected first degree relatives (moderate risk). Colonoscopy was initially offered
at five year intervals or three year intervals if an adenoma was detected. The
incidence of adenomas with high risk pathological features or cancer was
analysed by age, the extent of the family history, and findings on previous
colonoscopies. The cohort was flagged for cancer and death. Incidence of
colorectal cancer and mortality during > 15.000 person years of follow-up were
compared with those expected in the absence of surveillance. High risk
adenomas and cancer were most common in families with HNPCC (on initial
colonoscopy 5,7% and 0,9%, respectively). In the families with moderate risk,
these findings were particularly uncommon under age 45 (1,1% and 0%) and on
follow-up colonoscopy if advanced neoplasia was absent initially (1,7% and
0,1%). The incidence of colorectal cancer was substantially lower than the
expected incidence in the absence of surveillance when the family history was
taken into account: 80% in families with moderate risk (p = 0,00004), and 43%
in families with HNPCC (p = 0,06). The study showed clearly that colonoscopic
surveillance reduces the risk of colorectal cancer in people with a strong family
history; members of families with HNPCC require surveillance with short
intervals. Individuals with a lesser family history may not require surveillance
under age 45, and if advanced neoplasia is absent on initial colonoscopy,
surveillance intervals may be lengthened. This would reduce the demand for
colonoscopic surveillance.
In a multicenter, prospective controlled cohort trial 138 200 patients with normal
Flexible Sigmoidoscopy (FS) and 200 patients with diminutive adenomas on FS
were matched for age and gender. Diminutive adenomas (< 10 mm in diameter)
are frequently found during colon cancer screening with FS and the trial aimed
to assess the predictive value of these diminutive adenomas for advanced
adenomas in the proximal colon. All patients underwent colonoscopy. The
presence of advanced adenomas (adenoma 10 mm in diameter, villous
adenoma, adenoma with high grade dysplasia, and colon cancer) and adenomas
(any size) was recorded. Before colonoscopy, patients completed
questionnaires about risk factors for adenomas. The prevalence of advanced
adenomas in the proximal colon was similar in patients with diminutive
adenomas and patients with normal FS (6% vs. 5,5%, respectively - RR 1,1; 95%
CI: 0,5 - 2,6). Diminutive adenomas on FS did not accurately predict advanced
adenomas in the proximal colon: sensitivity was 52% (95% CI: 32% - 72%) and
specificity, 50% (95% CI: 49% - 51%); positive predictive value was 6% (95% CI:
4% - 8%) and negative predictive value was 95% (95% CI: 92% - 97%). Male
gender (odds ratio 1,63; 95% CI: 1,01 - 2,61) was associated with an increased
risk of proximal colon adenomas. The authors concluded that diminutive
adenomas on sigmoidoscopy may not accurately predict advanced adenomas in
the proximal colon.