The risk of colorectal adenomas in patients with duodenal adenomas.

Colorectal cancer is the third most common cancer and the second most common
cause of cancer related deaths. Most cases of colon cancer begin as small
adenomatous polyps. Through colonoscopic examinations these adenomas can be
detected and subsequently removed. It is generally accepted that, like
colorectal adenomas, duodenal adenomas also follow the adenoma-carcinoma
sequence. Curiously, despite numerous phenotypic similarities between the small
and large intestinal epithelia, including a very high cellular turnover, small
intestinal neoplasia is very rare compared with its colorectal counterpart [1].

In the known hereditary colon cancer syndromes, patients are at increased risk
of small bowel adenomatosis/cancer besides their generally high risk of
colorectal adenomas/cancer. For instance, in 40-90% of patients with familial
adenomatous polyposis (FAP) duodenal adenomatosis is found (2-6). These
adenomas are mainly situated around the ampulla Vateri. The lifetime risk of
developing duodenal cancer in FAP is 3-4% at the age of 70 (7). Most polyposis
patients develop hundreds of colorectal adenomas and without prophylactic
colectomy they inevitably develop colon cancer (8). Also in other hereditary
colon cancer syndromes (MUTYH-associated polyposis and hereditary non-polyposis
colorectal cancer) gene carriers have an increased risk of small bowel
adenomas/cancer besides their high risk of colonic adenomas/cancer.

Sporadic duodenal adenoma is an uncommon finding. In a large Scandinavian study
only 0.4% of 584 endoscopy patients had duodenal polyps, of which 7% were
adenomatous [9]. Most adenomas are found incidentally at endoscopy. To date, it
is unknown whether this group of patients is, like gene carriers in the
hereditary colon cancer syndromes, at increased risk of colorectal adenomas.
Several retrospective studies suggest an increased risk of colorectal neoplasia
in patients with duodenal adenomas. In a recent study, 73% of patients with
duodenal adenomas and without familial adenomatous polyposis had colonic
adenomas [11-13]. Also small intestinal carcinoma is associated with
colorectal carcinoma and vice versa [10]. However, the extent to which duodenal
adenomas are associated with colorectal adenomas is not well prospectively
studied.

In conclusion, an increased risk of colonic adenomas (and thus of colon cancer)
in patients with duodenal adenomas is likely. Therefore, the risk of colonic
adenomas in this group of patients should be calculated in order to advise
these patients whether they should undergo endoscopic examinations of their
colon. Because duodenal adenomas are an uncommon finding, a multicenter trial
should answer this question.

References
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Study the risk of colorectal adenomas in patients detected with duodenal
adenomas.

Prospectively collected data in three hospitals (Slotervaart Hospital
Amsterdam, University Medical Center Groningen, Leiden University Medical
Center).

If during colonoscopy polyps are detected, they will be removed if possible. If
a polyp is removed there is a small chance of bleeding or perforation. The
estimated risk of a compication is about 0.2%.