**6. Who is at risk of developing colorectal cancer**

There is strong tendency that countries with an obviously rising CRC incidence are more "Westernized" in lifestyle, especially in dietary habits, with increased consumption of high fat and protein but less fiber in diet. The change is more evident in urban areas than rural areas of the same country. Most of CRC is sporadic, i.e., caused by the interaction of genetic and environmentalfactorsviatheadenomacarcinomasequence,andcancermaytakeuptotenyears to develop in this way. Adenomas are more common with age, and one in four of the popula‐ tion aged over 50 will develop one or more polyps, with 10% of these polyps progressing to cancer over time.The most common indicator of high risk is a first-degree relative with CRC.

a risk of cancer that is three to four times as high as that among persons with negative tests, and that colonoscopy should be recommended for persons with these positive tests. In a recent study (Quintero et al) it has been shown that both iFOBT and colonoscopy are effective for detecting colorectal cancer but iFOBT is less effective for early detection of premalignant lesions (adenomas) than colonoscopy or sigmoidoscopy [57]. However, comparative studies have shown that iFOBT is more accurate than the gFOBT for the detection of colorectal cancer and advanced adenomas and this new test is now recommended as the first-choice fecal occult

Colorectal Cancer

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http://dx.doi.org/10.5772/53524

**Figure 6.** Dukes' stage of colorectal cancers detected by faecal occult blood test screening compared to those diag‐

Flexible sigmoidoscopy has also been used as a screening tool for CRC detection, as half of all cancers are seen in the rectum or sigmoid colon. There have been several studies suggesting benefit from flexible sigmoidoscopy, and their data suggest that flexible sigmoidoscopy would be an effective screening tool. Flexible sigmoidoscopy as an alternative to colonoscopy has the advantage that no oral bowel preparation is required, as the subject uses an enema that can be taken at home.The procedure is quick, requires no sedation and examines the left colon, which is the site of 75 per cent of all colorectal neoplasia. If CO2 insufflation is used, adenomas can be resected at the initial screening examination. This procedure does not, however, examine the right colon. For many clinicians and patients, colonoscopy is more appealing than flexible sigmoidoscopy because patients can be sedated and undergo a complete colon examination

Virtual colonoscopy, or computed tomography colonography (CTC), is another modality used to examine the colon. It has been suggested that this examination has fewer complications and

blood test in colorectal-cancer screening.

nosed in patients presenting with symptoms

**7.2. Flexible sigmoidoscopy**

with polypectomy.

**7.3. Virtual colonoscopy**
