The Prostate Cancer Antigen 3 (PCA3) test is a gene-based analysis that helps assess the likelihood of finding prostate cancer. It is not a diagnostic tool on its own, but provides supplementary information for individuals who may be at risk. The test measures the concentration of a specific genetic marker found at high levels in cancerous prostate cells. This information is particularly useful in clarifying ambiguous results from other tests and functions as a secondary tool to assist in medical decisions.
The PCA3 Test Procedure
The process for collecting a sample for the PCA3 test involves two steps. It begins with a digital rectal exam (DRE), where the physician massages the prostate for a short duration. This action is designed to encourage prostate cells, which may contain the PCA3 genetic marker, to be released into the urethra. Immediately following the prostate massage, the patient provides a urine sample. The first portion of urine is collected, as this part is most likely to contain the exfoliated prostate cells, and the sample is then stabilized for laboratory evaluation.
Candidates for the PCA3 Test
The PCA3 test is not used for general population screening; instead, it is recommended for individuals in specific clinical situations. A primary candidate is a man who has an elevated or consistently rising prostate-specific antigen (PSA) level but has undergone at least one prostate biopsy that returned a negative result. The PCA3 test helps determine if the elevated PSA is more likely to be caused by cancer, informing the decision about another biopsy. Another group that may benefit includes men on an active surveillance protocol for a previously diagnosed low-grade prostate cancer. For these individuals, the test can be used periodically to monitor the situation, as a change in the PCA3 score might suggest a change in the cancer’s status.
Understanding PCA3 Test Results
The output of the PCA3 test is a numerical score, calculated from the ratio of PCA3 messenger RNA (mRNA) to PSA mRNA in the urine sample. This score indicates the probability of finding prostate cancer if a biopsy were to be performed. The result is not a definitive diagnosis but a risk assessment tool that should be interpreted in the context of a person’s overall clinical picture, including their PSA levels. A low PCA3 score suggests a lower likelihood that cancer is present, which may lead a patient and their doctor to decide against an immediate biopsy. Conversely, a high PCA3 score indicates an increased probability of detecting cancer, with a score above 35 often associated with a higher chance of a positive biopsy.
How PCA3 Differs from the PSA Test
The PCA3 test and the more widely known PSA test differ in what they measure and how they are performed. The PSA test is a blood test that measures the level of a protein produced by prostate cells. This protein’s levels can be elevated for numerous reasons unrelated to cancer, such as an enlarged prostate or inflammation, which can lead to ambiguous results. The PCA3 analysis is performed on a urine sample collected after a DRE and specifically measures the overexpression of the Prostate Cancer Antigen 3 gene, which is highly specific to prostate cancer cells. Because the PCA3 gene is not significantly affected by non-cancerous conditions, it is considered more specific for cancer than the PSA protein, which is why it can help clarify the meaning of elevated PSA levels.