Tumor Markers
While they sound too vague for any explanation, tumor markers are so aptly named. By definition, they could be:
- Anything produced by cancer cells, benign or otherwise; or
- Anything produced by other cells in response to cancer activity.
In other words, as long as they provide cancer information, they can be called tumor markers. The information can be like how active the cancer is, or how targeted therapy is helping.
Circulating Tumor and Tumor Tissue Markers
How exactly do tumor markers help in cancer care? To better understand the answer to this question, you need to recognize the two major types of tumor markers: circulating tumor markers and tumor tissue markers.
Circulating Tumor Markers are the markers found in a patient's bodily fluids, such as urine, stool, or blood. These tumor markers are used in:
- Diagnosis – An increased level of tumor markers found in a patient's bodily fluids may be indicative of the presence of cancer.
- Determination of Prognosis – While on therapy or treatment, circulating tumor markers can be measured to see if the medication is working effectively. A steady level or significant increase may mean the treatment is not working, while a decline in measurement can be a sign of effective treatment.
- Determination of Relapse – After the completion of therapy or treatment, circulating tumor markers are measured to see if a relapse is happening. The lack of these tumor markers is often taken as good news.
Note: While they are extremely helpful, circulating tumor markers are not used on their own, especially in diagnosis, because they are ambivalent. For one, benign or noncancerous conditions may sometimes cause an increase in the level of circulating tumor markers. There is also a possibility that a patient has cancer, but he exhibits low levels of circulating tumor markers that are particular to the kind of cancer he is being checked on. For this reason, circulating tumor markers are used alongside other diagnostic tools such as imageries and biopsies.
An example of a Circulating Tumor Marker is CA125. CA125 is measured in the blood and is usually an indicator of ovarian cancer, although other types of cancer, like pancreatic, uterine, cervical, colon, and liver, also causes an increase in its level.
Tissue Tumor Markers are not “circulating”. They can be found in the tumor mass itself, often after a procedure, such as a biopsy. These tumor markers are used in:
- Diagnosis of Stage or Type of Cancer
- Determination of Prognosis
- Selection of Treatment
One good example of a tissue tumor marker is α-fetoprotein. Its level is measured in the blood. An elevated α-fetoprotein level in the blood is normal for a pregnant woman as it is produced by the growing fetus. However, if you’re an adult, man or woman, who is not pregnant, increased levels of alpha-fetoprotein can be indicative of ovarian, liver, or testicular cancer.
Ideal Tumor Marker
While there are several known tumor markers, some characteristics must be met for it to be considered as “ideal”. To be considered ideal, the tumor marker must at least be:
- Specific, meaning when you detect it, it can only be associated with one type of tumor.
- Sensitive, which means it cannot be detected unless the cancer is present. Markers that can be seen because of other physiological or noncancerous conditions are not sensitive.
- Of long-lead-time: This suggests that a diagnosis can be made before there is a change in the disease.
Of course, other characteristics, like affordability and accessibility are also taken into account, but the three characteristics mentioned above are the priority.
It’s safe to say that tumor markers have gone a long way in helping with oncologic studies and care; still, a lot of research is underway, so we can expect breakthroughs in the future.
References
- Tumor markers in clinical practice: General principles and guidelines. (2009, January). Retrieved April 23, 2020, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2902207/
- Tumor markers. (n.d.). Retrieved April 23, 2020, from https://www.cancer.gov/about-cancer/diagnosis-staging/diagnosis/tumor-markers-fact-sheet
- Tumor markers. (n.d.). Retrieved April 23, 2020, from https://stanfordhealthcare.org/medical-tests/t/tumor-markers.html
Authors footnote:
Tumor markers are generally not useful in screening or diagnosing cancer. However, once cancer has been diagnosed via biopsy or other investigations, tumor markers can be used to predict therapeutic responses and to monitor the effectiveness of cancer treatment.
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