Tumor markers are defined as substances produced by malignant or benign cells in response to the presence of cancer. They are detected by the examination of body fluids and tissue specimens. Their use includes tumor prediction, detection, and identification; monitoring of the course and prognosis; and evaluation of therapy protocols. The most desirable markers are those that can detect malignancy in a remote area by the analysis of body fluids (serum, urine, fluid from effusion, and CSF) rather than by invasive procedures to obtain a tissue sample. The markers are classified as endocrine (hormones), metabolic consequences associated with tumor (albumin, blood cells, lipids), enzymes and isozymes, oncofetal antigens or glycoproteins, and gene alteration or oncogenes. Current tumor markers and some clinical associations in use at this time are listed in Table 3-14.37,38 Panels of tumor markers to assist in the identification or confirmation of a malignancy in relation to tissue site and to assist in monitoring the course and prognosis of the malignancy are also performed.
Malignancies or cancer can invade organ tissues, access vascular channels, and metastasize to other body sites. They are characterized by an abnormal number of cells that grow without the normal control and immune abilities of the body. There is no single molecular or morphologic characteristic specific to malignancies.39 This allows for the presence of abnormal reference values associated with benign cells and conditions other than cancer. Complete specific test information regarding the blood cells, enzyme, hormone, endocrine, and metabolic markers listed in Table 3-14 is included in the respective chapters. These tests are commonly performed to obtain information about many other disorders, and differentiation is made when analyzing the results in the diagnosis of malignancy. Antigens and globulins, used in the diagnosis and treatment of cancer and commonly found in fetal life, are considered individually in this section. These substances are considered abnormal in adults if present in excessive amounts.