Would blood tests give any indication that you have cancer in the body? bowel cancer especially?

Colon Cancer: CEA is blood test associated w/colon Ca. However, not a good screening test - significant false +, can be high with benign conditions & in early Colon Ca CEA may not be elevated. Current gold standard for Colon Ca screening is colonoscopy. 2 other alternatives- virtual colonoscopy (CT) & a new stool DNA test just recently approved by FDA. Screen age 50, 40 if + family history Colon Ca or polyps