Tumor Marker

Introduction

Biomarkers are produced by cancerous cell or are secreted in response to cancers. These biomarkers are usually detected in blood or urine. The markers can be used for predicting risk of primary or secondary tumor. Occasionally, non-cancerous situations may also show increased level of some tumor markers than in normal conditions. In addition, some cancer patients does not have elevated level of tumor marker. Tumor markers are not the main parameters for diagnosis of cancer but may be employed as laboratory test as supportive to the diagnosis.

Types of Cancer Markers

The cancer markers can be hormones, oncofetal antigens, isoenzyme, proteins, mitochondrial markers, mucin, glycoproteins and molecular markers. Some of the biomarkers are calcitonin, human chorionic gonadotrophin, α fetoproteins, carcino-embryonic antigen, prostatic acid phosphatase, Immunoglobulins, catalase, mtDNA, cancer 125, p53, adenomatous polyposis coli etc.

Uses of Tumor Marker Detection

Though tumor markers are generally unsatisfactory for screening tests of occult cancers, when a specific tumor was diagnosed by means of a marker, the biomarker can be used as follow up of the treatment. Their level may also show the progression of the disease. Increased levels of tumor markers on detection results can be, but are not at all times bothersome. Though alteration of tumor marker levels can be the reason to alert, other noncancerous conditions may show variation in test result. The laboratory conditions for performing the tests can also change the results.

Advantages Of Tumor Marker Detection

• Tumor markers help in screening and early detection of cancer. Screening of tumor markers means to search for tumor markers in asymptomatic persons, whereas early detection means to detect markers at early stage of cancer.
• They help in the diagnosis of cancer. Both biopsy and tumor markers are employed to diagnose cancer. It is also capable to detect the origin of cancer in patients who are in advanced stages.
• They are also used to monitor the response to therapy. The originally elevated tumor marker level reduces on treatment indicating that the treatment is effective in reducing the cancer. Whereas if the level of tumor marker does not reduce on treatment, then the treatment is not efficient and should be changed.
• It can be used as prognosis of disease progression. Types of tumor marker aid in assessing the type of cancer and even the types of drugs to be used for treatment. 
• They indicate relapse of cancer in the course of follow-up period. Markers have also been employed for detecting cancers which recur subsequently initial treatment. Few tumor markers are useful in indicating the complete cure of cancer.

Disadvantages of Tumor Marker Detection

• As there is biological variability in patient’s sample, tumor markers are unable to predict specific cancer states.

• Variation in sample collection, handling or storage and reporting techniques can result into alteration in the protein profile of a given sample. Therefore, the methods of sample processing should be standardised before analysing the test results.
• The amount of cancer biomarkers is very less in early stage of cancer which makes it difficult to detect.

Methods for detection of tumor markers

Tumor markers are detected by antigen-antibody based techniques such as spectrophotometry, chromatographic techniques, radio-immunoassay (RIA), enzyme linked immunosorbent assay (ELISA), precipitin tests, flow-cytometry, immunohistochemistry and molecular genetic methods. Molecular genetic markers can be detected by polymerase chain reaction (PCR), reverse transcriptase- polymerase chain reaction (RT-PCR), southern blot hybridization (SB) and fluorescent in-situ hybridization (FISH).

Submitted by

Dr Pratyusha Kar

Faculty of Paramedical Sciences