Overview
A tumour marker refers to a substance that is produced by cancerous cells or other cells in the body as a response to certain cancerous or noncancerous conditions. These markers provide valuable information about a cancer, including its level of aggressiveness, potential response to treatment, and effectiveness of ongoing treatment.
Traditionally, tumour markers have been proteins or other substances that are produced in higher quantities by cancer cells compared to normal cells. They can be detected in the urine, stool, blood, tumours, or other tissues and body fluids of some cancer patients. However, there is an increasing focus on genomic markers, such as mutations in tumour genes, patterns of gene expression in tumours, and non-genetic changes in tumour DNA. These markers are found within the tumours themselves as well as in tumour fragments that are released into bodily fluids.
Numerous tumour markers have been identified and are currently used in clinical practice. Some markers are specific to particular types of cancer, while others are associated with multiple types of cancer.
Usage of tumour markers in cancer care
There exist two primary categories of tumour markers: tumour tissue markers and circulating tumour markers.
Circulating tumour markers are present in bodily fluids such as blood, stool, urine or in certain cancer patients. They serve various purposes, including:
- Prognosis estimation
- Determining the stage of cancer
- Detecting residual or recurrent cancer after treatment
- Assessing the effectiveness of a treatment
- Monitoring treatment response
While an elevated level of a circulating tumour marker may show the presence of cancer and aid in diagnosis, it is insufficient on its own. Some non-cancerous conditions can also cause an increase in certain tumour markers. Additionally, not all individuals with a specific type of cancer will exhibit elevated levels of the associated tumour marker. Hence, measuring circulating tumour markers is typically combined with other diagnostic tests like imaging techniques or biopsies to confirm cancer diagnosis.
Periodic measurements of tumour markers during cancer treatment, referred to as ‘serial measurements’, often holds more meaning than a single measurement. A decrease in the level of a circulating tumour marker may denote positive treatment response, whereas an increase level may suggest a lack of response.
After completing cancer treatment, circulating tumour markers are periodically measured to monitor for cancer recurrence.
Examples of mostly used circulating tumour markers include calcitonin (measured in blood) for medullary thyroid cancer, CA-125 (measured in blood) for ovarian cancer, and beta-2-microglobulin (measured in urine, blood, or cerebrospinal fluid) for chronic lymphocytic leukaemia, multiple myeloma, and few lymphomas.
Tumour tissue markers can be seen within the actual tumour itself and mostly in a biopsy sample. They are employed for the following purposes:
- Cancer diagnosis, staging, and classification
- Prognosis estimation
- Selection of appropriate treatment, such as targeted therapy
Tumour tissue markers indicating eligibility for specific targeted therapies are often known as biomarkers for the treatment of cancer. Genetic tests are usually conducted to detect variations in genes influencing cancer growth.
Examples of tumour tissue markers used as biomarkers for cancer treatment include progesterone receptor and oestrogen receptor testing in breast cancer patients for hormone therapy suitability, analysis of FGFR3 gene mutation for determining bladder cancer treatment, and PD-L1 testing to assess eligibility for immune checkpoint inhibitors in various cancer types.
Sometimes, tumours release genetic material and cells into the bloodstream, enabling the examination of biomarkers through blood samples. These liquid biopsies are still not used widely but offer several advantages. They are performed frequently than standard surgical biopsies since they do not require surgery. Liquid biopsies are particularly useful when it is difficult to access tumours or when patients cannot undergo surgical procedures. Liquid biopsy tests can often detect multiple cancer-associated biomarkers.
Tumour markers test
These tests aim to detect tumour markers, also known as cancer markers. Tumour markers are substances that can be produced by cancer cells or by normal cells as a response to cancer. For instance, certain proteins may be overproduced by specific cancer cells compared to normal cells. Tumour markers can also include changes in genes and other components of tumour cells.
Tumour markers can be identified in various bodily fluids, such as blood or urine. Additionally, samples of cells obtained during a biopsy from the tumour can contain tumour markers.
Tumour marker tests are primarily employed following a cancer diagnosis. The results of these tests can provide essential information about the cancer, such as its growth rate, the most suitable treatment options, the effectiveness of ongoing treatment, and the possibility of cancer recurrence.
It is important to note that not all cancers have established tumour markers, and even when known, these markers do not offer flawless information. This is because certain non-cancerous conditions can also lead to elevated levels of specific tumour markers, and some individuals may not produce high levels of commonly observed tumour markers in their specific type of cancer.
Despite these limitations, tumour marker testing, when combined with other tests and examinations, can often provide a more comprehensive understanding of an individual’s cancer.
What are they used for?
Tumour marker tests primarily serve the purpose of gaining additional information about a known cancer. However, there are certain circumstances where these tests may be employed for cancer screening or aiding in the diagnosis process.
Tumour marker tests are commonly utilized following a cancer diagnosis. When combined with other tests, these markers can assist in:
- Determining if the cancer has spread to other parts of the body (cancer stage)
- Predicting the rate of cancer growth, the likelihood of recovery, and the possibility of cancer recurrence
- Selecting the most suitable treatment for a specific type of cancer. Certain treatments are effective only for cancers that exhibit specific tumour markers. These markers used in treatment planning are also referred to as biomarkers
- Monitoring the effectiveness of ongoing treatment. A decrease in tumour marker levels generally indicates that the treatment is beneficial
- Detecting any remaining cancer cells after treatment or identifying cancer that reappears after treatment
Some tumour marker tests that involve body fluids (such as blood or urine) have a limited role in the screening process for certain types of cancer. These tests are primarily administered to individuals who:
- Possess a high risk of developing the specific cancer associated with the measured tumour marker. Exhibit symptoms that could potentially be attributed to that particular type of cancer.
- It is important to note that tumour marker tests employed for cancer screening do not provide a definitive cancer diagnosis. Elevated levels of tumour markers simply suggest a higher likelihood of cancer. To confirm or rule out cancer, a biopsy is typically required.
Tumour marker tests utilizing cells from a tumour, known as tumour cell markers, can aid in the diagnosis of cancer. These markers are typically obtained through a biopsy and, when combined with other tests, can confirm the presence of cancer and guide treatment decisions.
When does one need a tumour marker test?
If you fall into any of the following categories, you may require a tumour marker test:
- If you are presently undergoing cancer treatment.
- If you have completed cancer treatment.
- If you have a heightened risk of developing a specific type of cancer due to familial history or other risk factors.
The specific test you undergo will be determined by your overall health, medical history, cancer diagnosis, and any accompanying symptoms. Presented below are several commonly used tumour markers and their respective applications. It is important to note that certain tumour markers are specifically associated with particular types of cancer.
- Cancer Antigen 125: tumour marker for ovarian cancer
- Cancer Antigens 15-3 and 27-29: tumour markers for breast cancer
- Prostate-specific antigen: tumour marker for prostate cancer
- Carcinoembryonic antigen: tumour marker for colorectal cancer
- Alpha-fetoprotein: tumour marker for liver cancer
- Beta 2-microglobulin: tumour marker for multiple myeloma, leukaemia.
Procedure to conduct tumour marker test
A healthcare professional from your medical team will collect a blood or urine sample from you. The sample will be sent to a laboratory for testing. Certain tests need to be repeated periodically as the levels of tumour markers can fluctuate.
In addition to these tests, you will require other examinations to detect cancer and monitor the effectiveness of the treatment. This is necessary because tumour marker results have certain limitations and can occasionally provide inaccurate information. They might indicate the presence or growth of a tumour incorrectly, or falsely indicate the absence of a tumour or the effectiveness of the treatment.
What happens during a tumour marker test?
Blood tests are the most frequently utilized form of tumour marker tests, followed by urine tests and biopsies. Biopsies involve the extraction of a small tissue sample for examination, typically through a minor procedure.
- In the case of a blood test, a healthcare professional will draw a blood sample from a vein in your arm using a small needle. This procedure takes less than five minutes and may cause a slight stinging sensation as the needle is inserted or removed. The collected blood is then transferred into a test tube or vial for further analysis.
- When it comes to a urine test, your healthcare provider will provide you with specific instructions on how to provide the necessary sample.
- Regarding a biopsy, a healthcare provider will remove a small piece of tissue for evaluation. The method used for the biopsy depends on the location of the sample. For instance, a skin biopsy may involve cutting or scraping the area, while a biopsy of internal tissue might utilize a specialized needle or a small incision to extract all or part of a suspicious area.
Limits of tumour marker test
Tumour marker tests possess imperfections as they lack specificity for cancer and may lack sensitivity in detecting cancer recurrence. Merely detecting tumour markers alone is insufficient for diagnosing cancer, necessitating additional tests to gather further information regarding potential cancer or recurrence. Below are several limitations associated with tumour marker tests:
- Tumour marker levels can be elevated due to non-cancerous conditions or diseases.
- Individuals without cancer can exhibit elevated levels of tumour markers.
- Tumour marker levels may fluctuate over time, yielding inconsistent results across multiple tests.
- Tumour marker levels may not increase until the cancer progresses, rendering them ineffective for early cancer detection or high-risk individuals. Additionally, they may not indicate a cancer recurrence.
- Certain cancers do not produce detectable tumour markers in the bloodstream, while some types of cancer lack known tumour markers.
- Even if a specific type of cancer typically produces tumour markers, individual cases may not experience elevated tumour marker levels.
