My post won't make you feel better.
Most people with colon cancer (which I think you are alluding to) do not get symptoms until it is very advanced. My co-worker was diagnosed when she was 45. No symptoms. They found it when she went to her OB/GYN for her annual checkup. The OB/GYN did a rectal exam and examined part of her stool that they can get during this exam. It had blood in it when the chemical was added. They did another test, and there was still blood. So she immediately had a colonoscopy and there was cancer. She had no clue.
If you ever get to the point of passing visible blood in your stool and having symptoms you are in trouble. Occult blood means "hidden" blood. You can't see it, you won't see it. It occurs higher up in the colon and mixes with your stool and turns color. So, only a test can pick this up.
What kind of cancer does your brother have?