<prompt> Investigation of choice for diagnosis of CA colonColonoscopyDouble contrast barium enemaTriple phase CTViual colonoscopy  <response>: Colonoscopy is the gold standard for establishing the diagnosis of colon cancer. It permits biopsy of a tumour to verify the diagnosis while allowing inspection of the entire colon to exclude metachronous polyps or cancers; the incidence of a synchronous cancer is approximately 3. Colonoscopy is generally performed even after a cancer is detected by barium enema to obtain a biopsy specimen and to detect and remove small polyps that may be missed by the contrast studyRef: Sabiston, 20e, page: 1398 