Cancer (Tumour) Markers
Although not all cancers have a ‘cure’ to them, early diagnosis frequently provides the best chance for treatment & recovery. By now, the market is flooded with numerous cancer screening test kits & modalities. But which of them are proven & relevant?
Tumor markers are substances found at higher than normal levels in the blood, urine, or body tissues of some people with cancer. Although cancer cells often produce tumor markers, other cells in the body may also produce them. Screening tests are a way of detecting cancer early, before there are any symptoms. For a screening tests to be helpful, it should have high sensitivity and specificity. Sensitivity refers to the test’s ability to identify people who have the disease. Specificity refers to the test’s ability to identify people who do not have the disease. Most tumor markers used for screening are not sensitive or specific enough to accurately screen for cancer. As such, the results have to be interpreted together with other tests. A negative test result does not necessarily mean that there is no cancer present. A positive test also does not necessarily mean that there is cancer since other conditions such as inflammation can also cause the tumor markers to be elevated.
You should check with the doctors before opting to have tumour marker test done to screen for cancers since the rate of false positive and false negative results are very high.
Alpha Fetoprotein – AFP
AFP is an oncofetal protein formed in the foetal liver and the yolk sac. In normal adults the level is very low or negligible. High levels are seen in liver cancer and germ cell tumours of the testes and ovary. Not all cases of liver disease will show high levels of AFP. It is normal and common to see high levels of AFP in pregnant women as the level varies with the advancement of pregnancy. The AFP test is also performed on pregnant women to screen for congenital defects.
Carcinoembryonic Antigen – CEA
CEA is an oncofetal protein that is found in abundance in foetal life but normally absent or present in very low amount in adults. It is non-tissue specific as it is produced by a variety of cancers including cancers of the gastrointestinal tract, pancreas, lung, breast, ovary and cervix. If CEA level is high, the test should be repeated. Raised serum levels may however be present in benign diseases including inflammatory bowel disease, cirrhosis, pneumonia, pancreatitis and smokers. This index of suspicion is also useful for the early detection of tumour recurrence and spreading.
CA 19-9 (Cancer Antigen 19-9)
Serum CA 19-9 levels are raised in up to 80% of patients with pancreatic cancer, in 54-89% with stomach cancers and 64% with colorectal cancers. Occasionally, serum levels may be raised in benign diseases like acute and chronic pancreatitis, cystic fibrosis, inflammatory bowel disease and hepatobiliary tract disease. However, in benign diseases, it does not usually exceed 100 U/ml.
CA 125 (Cancer Antigen 125)
CA 125 is a glycoprotein that is produced by many ovarian cancers. CA 125 levels above 35 ng/ml are detected in 20-40% of patients with State I & II ovarian cancers and 96% of patients with State III and IV disease. Less commonly, levels may be raised in patients with cancers of the gastrointestinal tract, breast, cervix, endometrium and fallopian tube. Raised levels may be present in benign conditions like endometriosis and peritoneal inflammation. CA 125 is also useful for monitoring patients for response to treatment and for tumour recurrence.
Prostate Specific Antigen – PSA
PSA is produced in the prostate gland and useful in the diagnosis for prostate cancer as well as for monitoring patients for tumour recurrence and spreading. Normally, very little PSA is found in the blood. An increase in PSA levels may be due to benign prostatic hypertrophy, prostatitis, and/or prostate cancer.
CA 15.3 (Cancer Antigen 15.3)
CA 15.3 when used in conjunction with other clinical and diagnostic procedures is useful for monitoring the course of disease and therapy in metastasis breast cancer patients.
EBV EA IgA
The EBV test is specifically designed for differentiating nasopharyngeal carcinoma (NPC) patients from normal patients. The test consists of 4 highly NPC-specific polypeptides to aid the determination of human immunological response to NPC. The specificity and sensitivity are both above 95%. It should be noted that for diagnostic purpose, the positive result obtained must be correlated with other clinical and laboratory findings. Absence of antibodies does not exclude the possibility of NPC.
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