Current statistics indicate that 1 in 20 people in Australia will have bowel cancer at some stage - part of the issue is that there are very often no obvious symptoms at all of early stage bowel cancer, and it is much easier to treat early stage bowle cancer than it it to treat late stage bowel cancer.
For this reason, the National Bowel Cancer Screening Program was set up (in 2008) to offer a test called the FOBT - Faecal Occult Blood Test - which is able to detect minute, invisible amounts of blood in the stool. This does not in itself indicate bowel cancer, however if a test is positive for blood in the stool, a colonoscopy is recommended to investigate what is causing the bleeding. The Program is free for everyone aged 50-75 and it is recommended that the FOBT be conducted every 1-2 years by people in this age bracket.
Although it is a good indicator of the need for a colonoscopy, the FOBT can miss some smaller cancers and some polyps, so in some cases where the FOBT comes back negative, a colonoscopy may still be advised.