Cancer Markers are essentially just substances that are found in your blood when a blood test is taken and tested.
If you have a higher than normal blood or cancer markers in your blood then it can indicate cancer and is a way of telling if you might have cancer or not.
The normal range of cancer markers is less than 30 units/mL. CA 27.29 and anything higher than that then it could indicate cancer.
Cancer Markers are also substances found in urine and even your body tissue.