Tumor Markers
A tumor marker is a substance sometimes found in an increased amount in the blood, other body fluids or tissues that may suggest the presence of a type of cancer. They are measured qualitatively or quantitatively by chemical, immunological or molecular biological methods to identify the presence of cancer.
Potential uses of tumor markers:
Screening in general population (of limited value).
Differential diagnosis in symptomatic individuals in conjunction with clinical and radiological evidences.
Prognostic indicator of disease progression when the plasma concentration correlates with the tumour mass.
Evaluation of success of treatment.
Monitoring of response to therapy and detecting recurrence.
Tumor markers include:
Enzymes: elevated levels can serve as tumor markers, examples are:
Alkaline phosphatase (ALP): primary or secondary liver cancer, metastatic cancer with bone or liver involvement, specially with osteoblastic lesions.
Lactate dehydrogenase (LDH): liver cancer, non-Hodgkin’s lymphoma, acute leukemia, non-Seminomatous germ-cell testicular cancer, seminoma, neuroblastoma, etc ……
Prostatic acid phosphatase (PAP): prostatic cancer, osteogenic sarcoma, multiple myeloma, and some benign conditions such as benign prostatic hyperplasia, osteoporosis and hyperparathyroidism.
Prostate-specific antigen (PSA): it is extremely useful tumor marker to detect, stage, and monitor treatment of prostate cancer. Serum PSA rises also with age, benign prostatic hypertrophy and lower urinary tract infection
Hormones: production of hormones in cancer involves either production of hormones in excessive amounts by its original gland or production at a distant site by a non endocrine tissue (ectopic syndrome), e.g. production of ACTH by the small cell carcinoma of the lung.
Oncofetal antigens: are proteins produced during fetal life and decrease to low levels or disappear after birth. They reappear in individuals with cancer.
Alpha-fetoprotein (AFP): a marker for hepatocellular and germ-cell carcinoma (non-seminoma) its measurement can also used to monitor treatment. Level in healthy adults is less than 10 ug/L. [During pregnancy, maternal AFP levels start to show progressive increase]. Levels can also be increased in non-cancerous liver diseases such as hepatitis and cirrhosis, but the increase is mild.
Carcinoembryonic antigen (CEA): this is a marker for colorectal, gastrointestinal, lung and breast carcinoma. The upper limit in the healthy population is about 3 ug/L for non-smokers and 5 ug/L for smokers. Because of the false-positive and false-negative results, CEA testing is better used as an adjunct to clinical staging and together with other markers. CEA levels decline after successful therapy. Rising values may indicate recurrence.
Carbohydrate markers: These are either antigens on the tumor cell surface or secreted by the tumor cells. They tend to be more specific than enzymes or hormones and are abbreviated as CA. Examples are CA 15-3, CA 549 (for breast and ovary), and CA 125 (for ovary and endometrium).
Blood group antigens: These include CA 19-9 (colorectal and pancreatic cancer) and CA 72-4 (cancer of GIT and ovary).
In addition, proteins, hormone receptors and genetic markers are now used with various degrees of success.
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