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

34 Screening for Colorectal Cancer KCE reports vol.45
3 RISK STRATIFICATION FOR COLORECTAL
CANCER
3.1 INTRODUCTION
The majority, about 70 - 75% of patients with colorectal cancer, have sporadic
disease, with no apparent evidence of having inherited the disorder. The
remaining 25 - 30% of patients has a family history of colorectal cancer that
suggests a genetic contribution, common exposures among family members, or
a combination of both 47. Limiting screening or early cancer detection to only
these persons at increased risk would obviously miss the majority of colorectal
cancers.
Specific genetic mutations have been identified as the cause of inherited cancer
risk in some CRC-prone families. High penetrance dominant genes yielding
clinical syndromes such as familial adenomatous polyposis (FAP) and hereditary
non-polyposis colorectal cancer (HNPCC - Lynch syndrome) are estimated to
account for approximately 5% to 6% of colorectal cancer cases overall 48, 47. It is
likely that other yet undiscovered major genes and background genetic factors
contribute to the development of colorectal cancer.
Moderate familial clustering, on the other hand, represents a heterogeneous
group attributable to a combination of genes, environment, and chance.
This chapter does not deal with personal lifestyle, dietary nor environmental
risk factors. An excellent overview of these aspects can be found in the SIGN
National clinical guideline on management of colorectal cancer 49, on the
National Cancer Institute website 38 (USA) or on the Australian Cancer
Network website 50.
3.2 PERSONAL AND FAMILIAL HISTORY ELEMENTS
INDICATING INCREASED CRC RISK
Patients with the following history are to be considered as having a moderateto-high
lifetime risk of developing CRC51-54, 29, 55, 27, 56-58:
3.2.1 Personal history of adenomatous polyps
A personal history of adenomatous polyps is associated with an increased risk
of future development of additional polyps and of colorectal cancer. This risk
increases with sizes greater than 1 cm for any adenomatous polyp, the number
of polyps, and villous or tubulovillous histology 59-62.
Efforts to identify causes of CRC and to develop effective preventive measures
have led to the hypothesis that adenomatous polyps (adenomas) are precursors
for the vast majority of colorectal cancers. Evidence supporting the adenomacarcinoma
sequence in colorectal cancer is summarized in Table 5 63.