Tumor Markers; AFP, HCG, CA-125Tumormarkers are molecules occurring in blood or tissue that are associatedwith cancer and whose measurement or identification is useful inpatient diagnosis or clinical management. The ideal marker would be a'blood test' for cancer in wich a positive result would occur only inpatients with malignancy, one that would correlate with stage andresponse to treatment and that was easily and reproducibly measured. Notumor marker now available has met this ideal.Tumormarkers can be used for one of four purposes: (1) screening a healthypopulation or a high risk population for the presence of cancer; (2)making a diagnosis of cancer or of a specific type of cancer; (3)determining the prognosis in a patient; (4) monitoring the course in apatient in remission or while receiving surgery, radiation, orchemotherapy.Notest meets all of those requirements. Specifically, no marker has beenestablished as a pratical cancer screening tool either in a or in most high risk poulations. The reason for thisis the relative lack of sensitivity and specificity of the availabletests, given the low prevalence of cancers in most population groups.Given the low prevalence of cancer in general, even tests that arehighly sensitive and specific may have low predictive values.Tumormarkers include many substances that are not readily systematicallyorganized.Those discussed here are generally products or the cancercell, although none is unique to cancer cells; they represent aberranttumor production of a normal element. Some markers are produced by theorganism in response to the cancer's presence.Tumor AntigensIncludemarkers defined by both monoclonal antibodies and polyclonal antisera,often the so called oncofetal antigens. The oncofetal substances,present in embryo or fetus, diminish to low levels in the adult butreappear in the tumor.Carcinoembryonic AntigenTumormarker, CEA: Carcinoembryonic antigen (CEA) is a protein found in manytypes of cells but associated with tumors and the developing fetus.
Marker Test Null Values Examples
CEAis tested in blood. The normal range is. 0.0 - 5.0Hormones:Hormonesare produced by many tumors. The hormone may be a natural product ofits associated organ or represent abnormal synthesis reflectingunregulated cancer cell metabolism. Examples include insulin productionby islet cell tumor, calcitonin by medullary thyroid carcinoma, andcatecholamines by pheochromocytoma. Or it may be that the hormone isnot a natural product of its associated organ, in which case isdesignated 'ectopic'. Examples include the production of ACTH and ADHby lung cancers.Inthis section, discussion is limited to human chorionic gonadotropin.Other hormones will be discussed in another review.Human Chorionic GonadotropinHCGis a glycoprotein consisting of subunits a e b, which arenonconvalently linked.
The hormone is normally produced by thesyncytiotrophoblastic cells of the placenta and is elevated inpregnancy. Its most important uses as a tumor marker are in gestationaltrophoblastic disease and germ cell tumors.Allgestational trophoblastic tumors produce HCG, and it is a valuablemarker in these tumors, screening reliably in all cases and indicatingpoor responses to treatment. The level correlates with tumor mass andthus has prognostic value. HCG is extremely sensitive, being elevatedin women with minute amounts of tumor. The patient is followed weeklyduring treatment, and at the completion of treatment indefinite followup is advised to detect recurrence.
HCG is essential in managingtrophoblastic neoplasms.Thelevel of HCG is occasionally elevated in other cancers including thoseof breast, lung, and gastrointestinal tract, but in these diseases ithas found little clinical application.EnzymesInvestigatorsobserve either enzymes that are native to normal tissue or those thatcould be associated with changes in metabolism that are unique tocancer tissue.Acid PhosphataseThisenzyme is found in high concentraitions in the normal prostate as wellas in primary and metastatic prostate cancers. Acid Phosphatase mayalso originate from other tissues.Themore sensitive immunological test (RIA or counterimmunoelectrophoresisfor prostatic acid phosphatase, wich are specific for the enzyme ofprostate tissue) often gives positive results in the early stages ofdisease.Becauseof the reliability of acid phosphatase as a marker in early disease, itwas hoped that the test could be used as a screening tool. However, itmay also be elevated in up to 6 percent of cases of benign prostatichypertrophy and other conditions. Thus, its predictive value is low ontheoretical grounds.
So, acid phosphatase is useful in followingpatients with advanced disease.Neuron Specific EnolaseNeuronspecific enolase is an isozyme of the glycolytic pathway that is foundonly in brain and neuroendocrine tissue. Its an immunohistochemicalmarker for tumors of the central nervous system, neuroblastomas, andAPUD tumors.Useof NSE has been evaluated in lung cancer and neuroblastoma.Galactosyl Transferase IIGalactosylTransferase II, an isozyme of galactosyl transferase, has been shown tobe elevated in a variety of malignancies, predominantlygastrointestinal. In colon cancer its level correlated with the extentof disease and disease progression; in pancreatic cancer it was moresensitive and specific in distinguishing benign from malignant diseasethan CEA and other tests.ImmunoglobulinsProductionof a monoclonal immunoglobulin molecule is characteristic of multiplemyeloma. These paraproteins are usually complete antibody molecules butmay be isolated light chains or, rarely, heavy chains. They may belambda or kappa light chains and of any immunoglobulin subtype.Immunoglobulinsare valuable in the staging and treatment of myeloma, the amount ofparaprotein serving as an index of tumor volume. Response to treatmentis indicated by a fall in paraprotein production, whereas a rise pointsto relapse.