Tumor Markers

There is no blood exam that can definitively diagnose prostate cancer, or any cancer for that matter. At present, the procedure used to definitively diagnose cancers involves taking a sample of a suspected malignant tissue and examining it under the microscope. For solid tumors, this procedure is called a biopsy.

There is however a blood test that measures prostate specific antigen (PSA), but it is not diagnostic of prostate cancer because there are many conditions that give rise to an elevated blood PSA level, and sometimes, blood PSA level does not increase even if the person has prostate cancer. Currently, experts do not even agree on the value of PSA testing in screening for prostate cancer. In fact, the American Cancer Society does not support routine testing for prostate cancer at this time.

What is PSA then and what is it useful for?

PSA is a tumor marker. Tumor markers are substances—mostly proteins and hormones—that are present in higher than normal amounts in the body of some people with certain types of cancer. They are produced either by the body as a response to the presence of a cancer or by the cancer cells themselves.

There are now more than 20 established tumor markers that are used by physicians; many other potential ones are being studied. Examples of tumor markers aside from PSA are CA 15-3 and alpha fetoprotein. Tests for tumor markers utilize blood (as in the test for PSA), urine or body tissues as sample.

Some tumor markers are seen in several types of cancer (e.g., CA 15-3 is elevated in many cancers including breast, lung and ovarian); a few are specific for one type of cancer (e.g., PSA for prostate). However, regardless of their specificity, tumor markers, by themselves, are not used to diagnose cancer because most yield false positive results (i.e., their levels are sometimes elevated in people with benign tumors and conditions) as well as false negative results (i.e., their levels do not go up even if a cancer exists, especially if the malignancy is in its early stages).

Although they cannot definitively diagnose cancers, tests for tumor markers serve several purposes:

• They help detect and diagnose certain cancers when used with other tests (e.g., x-rays, MRI, etc.).

• Many help to determine the characteristics of a cancer: how aggressive it is; how fast it grows; how far it has spread into other tissues and organs; etc.  These data can help the physician in determining prognosis (i.e., ultimate outcome) of the disease. Prognosis and extent of spread dictates, to a large extent, the regimen to be followed in treating a cancer.

• They can be used as guide for treatment. For example, breast cancer patients who are positive for estrogen receptors (a tumor marker) can benefit from drugs that neutralizes the effects of estrogen while those who are negative for estrogen receptors will not. Likewise, only advance breast cancer patients who are positive for the tumor marker Her2/neu will respond to Herceptin drug treatment.

• Most are useful, especially in advanced cancers, in monitoring the patient’s response to treatment. If the level of the tumor marker that is being observed goes down, the treatment is working; otherwise, dosing adjustments or the application of other treatment modalities may be in order.

• They are used to detect recurrence. Thus, many cancer survivors undergo periodic test/s for tumor markers.

Source: Manila Bulletin, Photo Credit :  iamstillawoman.blogspot.com