EXAS tests stool specimens for evidence of specific genetic mutations which are linked - in a step by step apoorach- with invasive Colon Cancer. EXAS thus tries to diagnose, early, the presence of colon cancer, which is difficult to diagonise with non-invasive methods (the occult stool specimen test is notoriously nonspecific and not sensitive).
The German company Epigenomics (traded on the German stock market) tries something similar by examining epigenetic methylation patterns which are know to be different in cancerous and non cancerous cells. The giant American diagnostics company DGX has just added the Epigenomics test to its list of tests offered.
GHDX's colon Cancer test is done on the operated cancerous tissue of a patient known to suffer from Colon Cancer. The test will tell you if the patient has a low or high risk of tumor recurrence, and thus might need different therapeutic options, dependent on the risk profile.
MYGN (Myriad Genetics) tests the blood for genetic markers which provide information on whether you have a high or low risk of developping a certain ( often hereditary) cancer, such as some breast cancers, melanoma, etc.