PSA

Tumor markers are substances that can be detected in higher-than-normal amounts in the blood, urine, or body tissues of some patients with certain types of cancer. A tumor marker may be produced by a tumor itself or by the body in response to the presence of the cancer.

Tests for tumor markers may be used along with other tests or x-rays to detect and diagnose some cancers. Tumor marker tests are not used alone because most markers can be found in elevated levels in patients who have noncancerous conditions and because no tumor marker is specific to a particular type of cancer. Also, not every cancer patient has an elevated tumor marker level; this is especially true in the early stages of cancer, when tumor marker levels are often in the normal range. Although the use of tumor markers to diagnose cancer is limited at this time, researchers are seeking markers that are specific to a particular type of cancer and that can be used to detect the presence of cancer before symptoms appear.

Doctors may use changes in tumor marker levels to follow the course of the disease, to measure the effect of treatment, and to check for recurrence. In some cases, the tumor marker level reflects the extent of the disease (stage) or indicates how quickly the disease is likely to progress (prognosis).

Prostate-Specific Antigen (PSA)

Prostate-specific antigen (PSA) is a protein produced by both normal and abnormal prostate cells. The PSA level in the blood may be elevated in men who have a benign or a malignant (cancerous) growth in the prostate. For this reason, the PSA test does not always allow doctors to distinguish between benign prostate conditions (which are very common in older men) and cancer. However, an elevated PSA level may indicate that other tests are necessary to determine whether cancer is present.

The PSA test also is useful in monitoring the effectiveness of prostate cancer treatment over time. When the level of PSA in a patient's blood returns to normal after treatment, it usually means that the treatment has stopped the growth of the cancer. If the blood level of PSA rises, it may indicate that the cancer is growing again. Often, a single test that shows a mildly elevated PSA level may not be significant; test results normally show some variation over time. The doctor generally looks for trends, such as steadily increasing values rather than a single elevated result.

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