Tumor markers are molecules that have a greater concentration than it is normally found in blood, urine and / or tissues of patients with certain types of cancer.
Tumor markers are produced by the tumor or the body of the host as a response to the presence of cancer or some other benign condition.Their measurement and identification are useful for diagnosis, treatment of cancer and monitoring of successful cancer treatment.
The purpose of the measurement of tumor markers
Measuring tumor markers have four purposes:
1. Cancer detection for healthy people or people with a higher risk of developing cancer
2. Diagnosis of cancer or a particular type of cancer
3. Determination of the prognosis in patients with disease.
4. monitoring the course of healing and success of treatment after surgery, radiotherapy or chemotherapy
To date, about a hundred of tumor markers are discovered. The most famous are Carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), CA 125, CA 19-9, CA 15-3, CA 27-29, prostate specific antigen (PSA), prostatic acid phosphatase, human chorionic gonadotropin (HCG) , lactate dehydrogenase (LDH), neuron specific enolase (NSE), galactosyltransferase and immunoglobulins. .
There are known antibodies for the following cell "markers": neural tissue antigens (a marker of protein S-100), blood group antigens (tumor vascular markers as Factor VIII, CD 31, CD 34), intermediate filament – e.g.Vimetin serves to prove sarcoma, etc.
Perfect tumor marker
The perfect tumor marker is the one that can be detected in the blood and that is positive only in patients with malignant disease, the one whose concentration matches the stage of disease and response to treatment, which is secreted in only one tissue, and that is easily measured and repeated. In other words, ideal tumor marker should be highly specific (cannot be detected in healthy individuals), high sensitivity (can be detected in the initial stages of the disease) and correlates with stage and tumor size. Because of the great diversity of malignant tumors even in the same body, no tumor marker meets these criteria so far.
There is no marker that would be sufficiently practical and inexpensive and that can be widely used for healthy people in cancer diagnosis.
Measuring levels of tumor markers is useful when used in conjunction with other tests. Measuring their levels as the only diagnostic tests is not sufficient to diagnose cancer for the following reasons:
- Tumor markers may be elevated in people with certain benign conditions
- Tumor markers were not elevated in every person who suffers from cancer, particularly in the early stages of the disease
- Many tumor markers are not specific to a particular form of cancer but can be elevated in many types of malignant diseases.
The race for the detection of tumor markers began 150 years ago. The first tumor marker is discovered then, the so-called Bence Jones protein in the urine of the person suffering from multiple myeloma. Unfortunately, no marker is sufficiently sensitive or specific to a particular type of cancer and has not become a routine diagnostic test.
In the example of CEA, AFP and PSA we will try to approach these problems to our readers.
Carcinoembryonic antigen (CEA)
CEA is one of the first clinically used tumor markers. It belongs to a group oncofetal antigens that are normally excreted during embryonic and fetal development.In adults, they are found in very low concentrations, but tumors can secrete them again in large quantities. Although CEA was first recognized in patients with colon cancer, abnormal CEA blood level is specific neither for colon cancer nor for malignancy in general.
Elevated CEA levels are found in a variety of other cancers including melanoma, lymphoma, pancreatic cancer, gastric, cervical, kidney, thyroid, liver, ovarian, lung and breast cancer.However, is most often used in the diagnosis of colon cancer, especially in metastatic disease.
It can be found in benign conditions such as cirrhosis, inflammatory bowel disease, chronic pulmonary disease and inflammation of the pancreas. CEA is used to control recurrence of disease after treatment. Research shows that a rise in the level of CEA is usually preceded by several months of clinical signs of relapse. Therefore, measuring CEA levels should be done often.
AFP is important for the diagnosis of hepatocellular carcinoma (liver cancer) and may also be useful for screening. Elevated levels of AFP are more common in areas where hepatocellular carcinoma is endemic (Africa) and for patients positive for hepatitis B antigen (HBsAgis positive).Elevated AFP is one of the most reliable single indicators of malignant disease available. Therefore, it can be used as a method of screening the population for the risk of liver cancer development. AFP is rarely elevated in healthy individuals, and increased only in a few number of diseases. AFP is elevated in germ cell tumors and ovarian cancer. It is less frequently elevated in cancers of pancreas, stomach, colon and lung. This elevation is not necessarily associated with liver metastases.
Prostate specific antigen (PSA)
PSA is a glycoprotein whose role is most probably the degradation of the clot seed. It is present in the blood of all adult men in very low concentrations. It is produced by normal and abnormal prostate cells. Since it is being produced only by the prostate – it has at least one characteristic of an ideal tumor marker: tissue specificity.Elevated levels of PSA can be found in the blood of men with benign prostate diseases such as inflammation of the prostate (prostatitis) and benign prostatic hyperplasia (prostate enlargement in older people) and prostate cancer.Although PSA cannot differentiate benign from malignant condition, its increased value indicates the need for the inspection and additional tests to rule out or confirm the presence of cancer.
Measuring the levels of PSA is useful for monitoring the success of prostate cancer treatment and controlling the return of disease after the treatment. During the control a single value may show a medium to high values which does not necessarily indicate a tumor regrowth. It is important to follow the trend, or whether there is an increase in PSA when measured for a long time. One measure itself does not give us much information. Level of PSA corresponds to the stage and volume of cancer.
Scientists research PSA to enable the early detection of cancer in apparently healthy men and increase the reliability of tests to help distinguish benign from malignant condition.
The main purpose of determining the value of tumor markers is to monitor disease progression and response to therapeutic treatment. International Association ISOBM (International Society Of Oncodevelopmental Biology and Medicine) has established criteria for the interpretation of the findings of tumor markers: increased concentration for about 25% corresponds to progression (progression) disease and decrease of the marker concentration for more than 50% means a partial recovery (remission).
Tumor markers do not have specificity for the organ (other than PSA for prostate and thyroglobulin in thyroid gland), which is why they are not used to determine the localization of the tumor. Not every tumor will cause increased concentration of tumor markers in the blood. Therefore, it is clear that the tumor markers cannot be used as an isolated indicator in the diagnosis of malignant diseases.
It is the fact that increased concentration of markers in the blood, urine and cerebrospinal fluid may be referred to the existence of a malignant disease. Knowing the factors affecting the laboratory analysis of tumor markers (method of blood collection, laboratory methods of proof, taking certain medications, smoking, etc.) is important for the interpretation of the findings and the obtained values. If you take into account the fact that the laboratory values differ from person to person and from laboratory to laboratory, it is clear that a definitive diagnosis can only be set using (histopathologic) tissue analysis. However, new medical findings and the discovery of tumor markers, give great hope in the possible early cancer detection
If it could be used as a "screening-method", together with other diagnostic procedures, in particular with ultrasonic analysis, CT, and with the help of MRI, certain tumors can be detected at an earlier stage with a greater chance of cure.