Tumour Markers
Tumour markers are substances, often proteins, that are produced by the cancer tissue itself or sometimes by the body in response to cancer growth. Because some of these substances can be detected in body samples such as blood, urine, and tissue, these markers may be used, along with other tests and procedures, to help detect and diagnose some types of cancer, predict and monitor a person's response to certain treatments, and detect recurrence.
While quite a few tumour markers are available and have been found to be clinically useful, others are available but not ordered frequently because they have been found to be less sensitive and/or specific.
Limitations
While tumour marker tests can provide very useful information, they do have limitations:
- Many tumour markers may also be elevated in persons with conditions or diseases other than cancer.
- Some tumour markers are specific for a particular type of cancer, while others are seen in several different types of cancer.
- Not every person with a particular type of cancer will have an elevated level of the corresponding tumour marker.
- Not every cancer has a tumour marker that has been identified as associated with it.
Consequently, tumour markers alone are not diagnostic for cancer; for some types of cancer, they provide additional information that can be considered in conjunction with a patient's medical history and physical exam as well as other laboratory and/or imaging tests.
Alpha Fetoprotein
Alpha Fetoprotein (AFP) is produced whenever liver cells are regenerating. With chronic liver diseases, such as hepatitis and cirrhosis, AFP may be chronically elevated. Very high concentrations of AFP may be produced by certain tumours. This characteristic makes the AFP test useful as a tumour marker. Increased amounts of AFP are found in many people with a type of liver cancer called hepatocellular carcinoma and in a liver cancer occurring in infants called hepatoblastoma. They are also found in some people with cancers of the testicles or ovaries. AFP exists in several different variants. The standard AFP test is for a total AFP, one that measures all of the AFP variants together.
Carcinoembryonic Antigen
Carcinoembryonic Antigen (CEA) is a protein that is present in certain tissues of a developing baby (fetus). By the time a baby is born, it drops to a very low level. In adults, CEA is normally present at very low levels in the blood but may be elevated with certain types of cancer. This test measures the amount of CEA in the blood to help evaluate individuals diagnosed with cancer.
CEA is a tumour marker. Originally, it was thought that CEA was a specific marker for colon cancer, but further study has shown that an increase in CEA may be seen in a wide variety of other cancers. CEA can also be increased in some non-cancer-related conditions, such as inflammation, cirrhosis, peptic ulcer, ulcerative colitis, rectal polyps, emphysema, and benign breast disease, and in smokers. For this reason, it is not useful as a general cancer screening tool, but it does have a role in evaluating response to cancer treatment. When an individual has been diagnosed with cancer, an initial baseline test for CEA may be performed. If this level is elevated, then subsequent serial testing of CEA may be performed to monitor the cancer as the individual undergoes treatment.
Cancer Antigen CA125
CA125 is a protein that is present on the surface of most, but not all, ovarian cancer cells. This makes the test useful as a tumour marker in specific circumstances. Significantly elevated concentrations of CA-125 may be present in the blood of a woman who has ovarian cancer. Thus the test may be used to monitor the effectiveness of treatment and/or for recurrence of the cancer. However, not all women with ovarian cancer will have elevated CA-125 so the test may not be useful in all cases.
Cancer Antigen 15-3 (CA15-3)
CA 15-3 is a protein that is produced by normal breast cells. In many people with cancerous breast tumours, there is an increased production of CA 15-3 and the related cancer antigen 27.29. CA 15-3 does not cause cancer; rather, it is shed by the tumour cells and enters the blood.
Since CA 15-3 can be measured in the blood, it is useful as a tumour marker to follow the course of the cancer. CA 15-3 is elevated in fewer than 50% of women with early localised, breast cancer or with a small tumour, but is elevated in about 80% of those with breast cancer that has spread (metastatic). Because not all women with invasive breast cancer will have elevated CA 15-3, the test is not useful in all cases.
CA 15-3 is not recommended as a screening test to detect breast cancer in women because it is non-specific. It may also be elevated in healthy people and in individuals with other cancers such as colon, lung, pancreas, ovarian, or prostate malignancies or certain conditions such as cirrhosis, hepatitis, and benign breast disease.
Cancer antigen 19-9 (CA 19-9)
CA19.9 is a protein that exists on the surface of certain cancer cells. CA 19-9 does not cause cancer; rather, it is shed by the tumour cells and can be detected by laboratory tests in blood and sometimes other body fluids.
Since CA 19-9 can be measured in blood, it is useful as a tumour marker to follow the course of the cancer. CA 19-9 is elevated in about 70% to 95% of people with advanced pancreatic cancer. However, CA 19-9 may also be elevated in other cancers, conditions, and diseases such as: gallbladder and bile duct cancers (cholangiocarcinoma), colorectal cancer, gastric cancers, ovarian cancer, lung cancer, liver cancer, bile duct obstruction (e.g., gallstones), pancreatitis, cystic fibrosis, thyroid disease, and liver disease. Small amounts of CA 19-9 are present in the blood of healthy people. Since CA 19-9 is not specific for pancreatic cancer, it cannot be used by itself for screening or diagnosis.
Prostate Specific Antigen (PSA)
PSA is a protein produced primarily by cells in the prostate, a small gland in males that encircles the urethra and produces a fluid that makes up part of semen. Most of the PSA that the prostate produces is released into this fluid, but small amounts of it are also released into the blood. PSA exists in two main forms in the blood: complexed (cPSA, bound to other proteins) and free (fPSA, not bound). The most frequently used PSA test is the total PSA, which measures the sum of cPSA and fPSA in the blood.
The PSA test may be used as a tumour marker to screen for and to monitor prostate cancer. The goal of screening is to detect prostate cancer while it is still confined to the prostate. However, most experts agree that screening should be done on asymptomatic men only after thorough discussions with their healthcare practitioners on the benefits and risks and after informed decisions are made to undergo screening. Elevated blood levels of PSA are associated with prostate cancer, but they may also be seen with inflammation of the prostate (prostatitis) and benign prostatic hyperplasia (BPH).
PSA is not diagnostic of cancer. The gold standard for identifying prostate cancer is the prostate biopsy, collecting small samples of prostate tissue and identifying abnormal cells under the microscope. An elevated PSA may be followed by a biopsy, which has risk of complications such as pain, fever, blood in the urine, or urinary tract infection.
Free Prostate Specific Antigen (fPSA)
PSA exists in two main forms in the blood: complexed (cPSA, bound to other proteins) and free (fPSA, not bound). The free PSA test may be used to help to determine whether a biopsy should be done when the total PSA is only slightly elevated. Men with BPH tend to have higher levels of free PSA and men with prostate cancer tend to have lower amounts of free PSA. A relatively low percentage of free PSA (% fPSA) increases the chances that a cancer is present, even if the total PSA is not significantly elevated.
Source: Testing.com - https://www.testing.com/
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