Sometimes the bleeding is not visible, so most physicians will do a simple test on your stool when you get an annual check-up. They may even want to do two or three, because early colon cancers may bleed only intermittently. You can buy these tests and do them at home if you wish. Unfortunately these tests are far from perfect. They miss many cancers and are falsely positive when no cancer is present, leading to unnecessary worry and excessive further evaluations.
Hemorrhoids bleed, too.
So don't let your hemorrhoids dissuade you from further efforts to detect a cancer, because colon cancers are more common in folks with hemorrhoids. Diagnosis Most physicians will put a finger inside your rectum to search for low-lying cancers. The next step beyond that in searching for a colon cancer is looking directly at the large bowel, a procedure that will detect nearly all of them. Technology over the past thirty years has developed a remarkable set of instruments that can look almost anywhere. An image focused on an array of thousands of these will carry that image to the other end of the array, where it can be seen or projected onto a screen.