The Use of Tumour Markers - Essay Example

Discuss the clinical uses of tumour markers currently measured in the clinical biochemistry laboratory and comment on potential future developments within this field. The increased focus on evidence-based medicine has resulted in the development of many chemical and molecular markers for diagnostic and treatment purposes. Tumour markers are chemicals or biological compounds that are normally produced by healthy cells, but are produced in elevated levels by cancerous tissues, or in response by the normal cells to cancerous growth. Additionally, when some metabolic pathway or function is affected by cancer, normal tissues could break down resulting in increased concentrations of analytes that also serve as markers for malignancies. Therefore, it is important to understand that it is the quantity and not just the presence of these compounds that must be considered in assessing the clinical use of tumour markers. Tumour markers are usually proteins (structural proteins and enzymes), cell-surface carbohydrate antigens, cellular receptors, and genes, which are detected in tissue, urine, and blood samples. Markers can be specific for a certain type of cancer, while there are markers that are common for different cancer types. Some markers also show increased concentration in the tissues and body fluids even in the absence of cancers. Due to this, tumour markers by alone should not be used in to diagnose cancer. In an ideal situation, screening and early diagnosis of cancer are the major goals for using tumour markers. To be able to do this, a marker must be highly specific for a certain cancer. It must not come up with too many false positive results that could lead to unnecessary and expensive follow-up tests, not to mention the psychological effects that come with the possibility of having cancer. Markers levels should be elevated enough, and ideally can be used to screen asymptomatic individuals, meaning that they can be used to detect cancer early. However, because markers are present in low concentrations in the body, screening for asymptomatic individuals is only recommended for those who have a genetic predisposition towards getting cancer. Currently, only the Prostate Specific Antigen (PSA) has been recommended and approved for general screening of prostate cancer in men over 50. A positive screening result for PSA is still not an indication of cancer, and PSA screening should be done in conjunction with a digital rectal examination of the prostate gland for diagnostic purposes. Markers are used to identify the local source of metastasized cancers, and could therefore aid in making a correct diagnosis. The recurrence of cancer can be checked by testing the levels of a certain analyte after cancer has been successfully treated. Tumour volumes can also be estimated using marker technology. Markers will give an indication of progression of the disease, its aggressiveness, and involvement in metastasis. The general uses of tumour markers are in (1) diagnosis of cancer, (2) monitoring for the recurrence of cancer; (3) prognosis and identifying the cancer stage; (4) detection of residual cancer; (5) screening; and (6) monitoring effectiveness of treatments like surgery, chemotherapy, and radiotherapy. Residual cancers can be detected after cancer surgery. In general, levels of the markers will drop if treatment is beneficial and will remain elevated or increase if it is ineffective. Markers that are highly used are α-fetoprotein (AFP), cancer antigens CA125, CA 15-3, CA 27.29, CA 19-9, carcinoembryonic antigen (CEA), choriogonadotropin (hCG), prostate specific antigen (PSA), and thyroglobulin (Tg). AFP tests germ cell malignancies of the testis and ovary and for liver cancer. CA-125 is a test used for ovarian and endometrial cancers; it is particularly useful in identifying stage I ovarian cancer. Because its concentration increases by more than 90% relative to normal, it is found in abnormally high amounts in advanced stages. CA-125 is very useful in assessing the effectiveness of cancer therapy, and in monitoring recurrence of the cancer. CA 15-3 and CA 27.29 are different epitopes of the same antigen and are primarily used to monitor therapy in patients with breast cancers, but concentrations of these antigens are also elevated in other cancers. So an initial finding of increased levels of CA 15-3 and CA 27.29 should be checked as to what cancer they indicate. They are relevant in evaluating the recurrence of breast cancer, assessment of prognosis, and checking for residual disease following surgery. CA19-9 is elevated in breast, gastric, liver, and colorectal cancers, but is most used in staging pancreatic cancer. CA 19-9 correlates well with pancreatic cancer stage, and are used successfully in deciding for surgery. A highly organ-specific marker is thyroglobulin (Tg) which is used to assess the thyroglobulin concentration in patients with differentiated thyroid cancer who are candidates for surgery. Before surgery or radioablation, thyroglobulin concentration is determined to check whether the tumour is producing thyroglobulin. If the tumour does produce thyroglobulin, then it can be used as a tool for assessing effectiveness of surgery and radioablation. The pre-surgery concentration is used as a reference value and is compared to post-surgery levels in order to check if the malignancy has been removed. Ideal thyroglobulin levels should be undetectable; any increase will indicate residual disease or recurrence of the cancer. In routine analysis, physicians use only several well-established markers. Research continues for other markers with potential use. Markers that can have potentially beneficial applications could prove to be as useful or more useful as the ones currently in use. It is apparent from the foregoing discussion that currently, markers are used primarily in the evaluation of the effectiveness of a given therapy, and for monitoring the recurrence of cancer in the patients who have undergone treatment. However, this has not resulted in significant improvement in patient outcomes even when the recurrence was detected early. Therefore, in this scenario, the markers serve only as warning that treatment has failed and other therapeutic options need to be given. A review of the most recent researches and advances in tumour marker development show that more potential markers are discovered and tested. However, the clinical usefulness of these markers is doubtful, despite early promising results. The conduct of marker research is being standardized to come up with quality results that are clinically useful. Research policy-making bodies have formulated guidelines for conducting and reporting studies on development of tumour markers. The guidelines set should pave the way towards more rigorous and effective evaluation of potential markers. It remains that even the most current markers lack sensitivity for screening and early detection of cancer. The lack of sensitivity is still the major shortcoming of tumour markers. Early detection of cancer is very important because increases positive prognosis and reduces cancer mortality. Therefore, the improvement of specificity and sensitivity should be the major goal in discovering and developing tumour markers. To increase sensitivity, studies should focus on a very clear understanding on the molecular basis of specific cancer development, and the role of compounds involved in the metabolic pathways. The complexities in the metabolic pathways are the major and ever-present challenges that researchers face. Read More