An ideal tumor marker for a cancer should be specific to that cancer and not generate false positive results. Research is still underway to identify specific markers for different types of cancers.

Tumor markers are substances, mostly proteins, that are produced by the body or by the tumor itself in response to cancer. These substances may be detected in elevated quantities in the blood, body tissue or urine of affected individuals. If the concentration of the markers is elevated then there is a need to monitor the patient for malignancies.

Tumor markers may be specific for a particular cancer or may be common to a few types of cancers. Alternatively, tumor markers may be present in non-cancerous conditions as well. In this case, these conditions should be ruled out before focusing on cancer.

The prerequisite for a tumor marker is that it needs to be specific and not generate false positive results. The ideal tumor marker (detected by a blood test) for a cancer will test positive for that malignancies alone, will help to diagnose cancer at the earliest and will help in deciding the   effectiveness of the treatment. So far no ‘model marker’ has been detected.

There are several markers that have been identified, but that had to be shelved due to their non-specificity. This is due to the overlap that occurs between different cancer tissues and the various markers produced by them. As a result, there are just a handful of markers that have been ear-marked   by health-care specialists to be used as diagnostic or prognostic tools.

Research is still underway to identify specific markers for different types of cancers.  The most widely accepted tumor marker to date is the Prostate Specific Antigen (PSA) used in the diagnosis and management of prostate cancer.

Tumor markers must not be confused with particular gene mutations that are risk factors for certain kind of cancers. Classical examples are inherited mutations in the genes BRCA1 and BRCA2, which can place a person at a higher risk for breast and ovarian cancer. However it is not mandatory that these people develop the cancer.

Tumor marker testing is primarily used for: –

1. Diagnosing cancer in an individual

2. Identify the type of cancer

3. Evaluating - the prognosis in a patient

4. Screening a healthy or a high- risk population for cancer. These tests provide the specialists with useful information about the disease and also provides a greater insight into disease progression.

Some of the common tumor markers and the associated disease conditions are discussed in the following sections.