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There are several limitations to the PSA test:
- Detection does not always mean saving lives: Even though the PSA test can detect small tumors, finding a small tumor does not necessarily reduce a man's chances of dying from prostate cancer. The test may identify slow-growing tumors that are unlikely to threaten a man's life. Also, it may not help a man with a fast-growing or aggressive cancer that has already spread to other parts of his body before being detected.
- False-positive tests: False-positive test results (also called false positives) occur when the PSA level is elevated but no cancer is actually present. False positives may lead to additional medical procedures that have potential risks and significant financial costs, and can create anxiety for the patient and his family. Most men with an elevated PSA test turn out not to have cancer; only 25 to 30 percent of men who have a biopsy due to elevated PSA levels actually have prostate cancer.
- False-negative tests: False-negative test results (also called false negatives) occur when the PSA level is in the normal range even though prostate cancer is actually present. Most prostate cancers are slow-growing and may exist for decades before they are large enough to cause symptoms. Subsequent PSA tests may indicate a problem before the disease progresses significantly.
Using the PSA test to screen men for prostate cancer is controversial because it is not yet known if the test actually saves lives. Moreover, it is not clear if the benefits of PSA screening outweigh the risks of follow-up diagnostic tests and cancer treatments.
For example, the PSA test may detect small cancers that would never become life-threatening. This situation, called overdiagnosis, puts men at risk for complications from unnecessary treatment, such as surgery or radiation. The procedure used to diagnose prostate cancer (prostate biopsy) may cause side effects, including bleeding and infection. Prostate cancer treatment may cause incontinence (inability to control urine flow) and erectile dysfunction (erections inadequate for intercourse).
For these reasons, it is important that the benefits and risks of diagnostic procedures and treatment be taken into account when considering whether to undertake a PSA test for prostate cancer screening.