Blood tests do not always detect cancer. Although tumor markers are now a common test for detecting cancer, they are not very satisfactory in terms of specificity and sensitivity. Sometimes an elevated tumor marker does not indicate the presence of cancer, but only the presence of inflammatory trauma in a system. In addition, it cannot pinpoint which organ has the problem, which means the specificity is not strong and further CT or MRI should be done. Tumor markers can even be normal when certain cancers appear, indicating that the sensitivity of the marker is not good, therefore tumor markers cannot be used to determine the presence or absence of cancer.