PSA and PSMA: What is the Difference? 

Prostate cancer is the second most common cause of cancer in men worldwide as of 2020, and cases of advanced prostate cancer continue to rise. 

Early detection of prostate cancer is essential for effective treatment. Dana-Farber physicians recommend having a conversation with a medical professional about screening around the age of 40, or perhaps even earlier, if you have a family history of prostate cancer.  

One screening option for prostate cancer is the prostate-specific antigen (PSA) test. This should not be confused with the prostate-specific membrane antigen (PSMA) test. PSA and PSMA are two biomarkers — a molecule, often found in the blood, that is a sign of disease — that are commonly used to detect prostate cancer. Despite the similarity in acronyms these two biomarkers have vastly different applications in clinical settings. 

PSA (prostate-specific antigen) test 

PSA is a protein produced by the prostate gland. High levels of PSA in the blood can be a sign of prostate cancer, but high PSA can also be caused by other conditions, such as an enlarged prostate or an infection.  

Annual PSA blood tests are easy ways to screen for prostate cancer. Through these tests, a primary care physician can monitor PSA levels and, if they are concerningly high, facilitate a referral to a urologist for an evaluation of the prostate or a prostate biopsy. It’s important to discuss PSA testing with your physician to best weigh the advantages against the possible drawbacks. 

PSMA (prostate-specific membrane antigen) imaging 

PSMA is a protein usually found on the surface of prostate cancer cells. It is not present on normal prostate cells. It’s also not identified through a blood test like PSA. Rather, it is found through an imaging procedure called PSMA-PET, which is ideal for finding whether prostate cancer has spread and where. 

This novel imaging technique uses a radioactive tracer which binds to PSMA on cancer cells. Those cells then “light up” under a PET scan, allowing doctors to see where prostate cancer has spread in the body, or, in other words, if it has metastasized.  

Which test is right for me?  

While both PSA and PSMA are important biomarkers targeted in the detection and treatment of prostate cancer, they are applied in widely different settings. PSMA imaging is used for patients that already have prostate cancer to monitor treatment and to detect whether the cancer has spread.  

PSA blood tests are administered to track known prostate cancer as well as to screen. You should discuss this test with your physician when you reach 40. 

Patients should discuss all screening options with their doctors to determine which one is best for them. This conversation may include other options such as digital rectal exams, especially if you have an increased risk of developing prostate cancer. 

About the Medical Reviewer

Dr. Mark Pomerantz is a medical oncologist at the Dana-Farber Cancer Institute. Dr. Pomerantz received his undergraduate degree from Yale University and his medical degree from Stanford University. He trained in Internal Medicine at Brigham and Women's Hospital in Boston, Massachusetts. He then pursued a fellowship in Medical Oncology at the Dana-Farber Cancer Institute in Boston. Dr. Pomerantz received his post-doctoral training in cancer genetics with Dr. Matthew Freedman at the Dana-Farber Cancer Institute and the Broad Institute of Harvard and MIT. He is on faculty at the Dana-Farber Cancer Institute in the Lank Center for Genitourinary Oncology.