Current Tissue Molecular Markers in Colorectal Cancer: A Literature Review
Table 3
Current screening options.
Screening options
Fecal screening tests
These tests search for occult blood in stool, which is nonspecific but can be detected especially in larger polyps and CRC. It is important to collect samples from consecutive bowel movements [39, 40]. Guaiac fecal occult blood test (gFOBT) detects qualitatively heme in the stool, using a guaiac material to which hydroperoxidase is added. Heme promotes a process that leads to the guaiac’s oxygenation and to a blue discoloration [41, 42]. It has a low sensitivity for the detection of CRC, but when performed every year or two, mortality is reduced [39, 43, 44]. Fecal immunochemical tests (FITs) use monoclonal or polyclonal antibodies to detect human haemoglobin. They can give qualitative or quantitative results. FIT is more accurate than gFOBT, because it does not react with nonhuman heme and is less sensitive to upper gastrointestinal tract’s bleeding [41, 45].
Endoscopic screening
Flexible Sigmoidoscopy is a screening option that allows examining the rectum and the lower part of the colon. It is an invasive technique that requires simple bowel preparation but cannot detect lesion in the whole colon [41, 45]. Colonoscopy is esteemed as the gold standard for CRC screening; it allows exploring the whole colon and removing the suspicious lesions [46, 47]. It is an invasive and expensive exam that must be performed if any other test has a positive result [39]. The most common side effect is postpolypectomy bleeding, but also tearing and perforation may be possible [45]. It is recommended that colonoscopy be practiced every 10 years in average-risk patients that underwent to a complete, negative exam [39, 48, 49].
CT-colonography (CTC)
CTC is a noninvasive test that has become a common method for CRC screening. It requires a bowel preparation, but sedation is not needed. The estimated sensitivity and sensibility in detecting polyps > 1 cm are high, above 90%. Limitation of this technique includes low sensitivity for small lesion and serrated polyps, the exposure to radiation, and the need of follow-up for extra colic incidental findings [39, 49–51].
