How do they test for colon cancer? not screening but diagnosing.

Biopsy: A biopsy specimen from usually a colonoscopy is usually examined by pathlogists to diagnose colon cancer.

Colonoscopy.: Colonoscopy of your colon is the best noninvasive test to diagnose whether or not you have a polyp, or cancer or other disease. However, although this can diagnose colon cancer, and do biopsies and remove polyps, it is expensive, and surgery might show something different, or more than was seen. Sigmoidoscopy is also good.

Colonoscopy: A colonoscopy evaluates the whole colon directly and if a mass or lesion is identified, it can be removed or biopsied. If you could only have one test, that would probably be the one to choose.