Various technologies are available for the diagnosis of adenomas and CRC {1-3}.

Colonoscopy is the gold standard and allows biopsy for histology. Biopsy is mandatory, usually at endoscopy. Double-contrast barium enema can visualize the large bowel; now it is superseded by CT colonography. Endoanal ultrasound and pelvic MRI are used for staging rectal cancer. Chest, abdominal and pelvic MRI scanning are utilised to evaluate tumour size, local spread and liver and lung metastases. PET scanning is performed for detecting occult metastases and for evaluation of suspicious lesions found on CT or MR. MR is also useful for evaluating suspicious lesion found on CT or US, especially in the liver. CEA is useful for follow-up, rising level suggest recurrence {1-3}.

 

FOBTs are used for mass population screening and are of value in hospital or general practice. Early diagnosis by screening asymptomatic persons with FOBT, >50% of all colon cancers are within reach of a 60-cm flexible sigmoidoscope; air-contrast barium enema will diagnose around 85% of colon cancer not within reach of sigmoidoscope; colonoscopy is most sensitive and specific, permits tumour biopsy and removal of synchronous polypus, but is more expensive. Radiographic or virtual colonoscopy has not been shown to be better diagnostic method than colonoscopy {1-3}.

Annual digital rectal exam and FOBT are recommended for patients over age 40, screening by flexible sigmoidoscopy every 3 years after age 50; careful evaluation of all patients with positive occult blood test (flexible sigmoidoscopy and air-contrast barium enema or colonoscopy alone) reveals polyps in 20-40% and carcinoma in around 5%.

Several screening tests for CRC are available, classified according to three categories {61}:

Stool-based techniques: Faecal occult blood test (FOBT) (either guaiac, so called gFOBT and immunochemical, so called FIT); Faecal DNA testing.   Endoscopic techniques: Optical colonoscopy, Flexible sigmoidoscopy (FS).   Imaging techniques: Virtual colonoscopy techniques using: a) Computed tomographic colonography (CT colonography), b) Magnetic resonance colonography (MR colonography); Wireless capsule endoscopy (PillCam Colon); Double-contrast barium enema (DCBE).   Faecal DNA tests represent a new group of fecal tests designed to detect molecular abnormalities in cancer or precancerous lesion that are shed into the stool. Two faecal DNA tests were commercially available: PreGen Plus, from 2003 to 2008, and ColoSure (single marker faecal DNA assay for methylated vimentin), intended for individuals who are not eligible for more invasive CRC screening. New test showed evolution in the composition of the test, as well in pre-analytical factors and analytic factors in comparison with older faecal DNA tests. Authors of the 2012 AHRQ HTA Report concluded that faecal DNA tests have insufficient evidence about its diagnostic accuracy to screen for colorectal cancer in asymptomatic, average-risk patients; insufficient evidence for the harms, analytic validity, and acceptability of testing in comparison to other screening modalities. Existing evidence has little or no applicability to currently available faecal DNA testing {62}.