President Joe Biden's last known prostate-specific antigen (PSA) test was in 2014, as questions arise about how much his cancer has spread and why it wasn't caught earlier."President Biden's last known PSA was in 2014. Prior to Friday, President Biden had never been diagnosed with prostate cancer," a Biden spokesperson told Fox News.The PSA test is a blood test used primarily to screen for prostate cancer. The test measures the amount of prostate-specific antigen (PSA) in the blood, according to the Mayo Clinic.DAVE PORTNOY GOES OFF ON BIDEN'S LATE CANCER DIAGNOSIS AS ONE OF THE GREATEST SCANDALS IN US POLITICSPSA is a protein produced by both cancerous and noncancerous tissue in the prostate, a small gland that sits below the bladder in males. It's mostly found in semen, which is also produced in the prostate, the Mayo Clinic said.Small amounts of PSA ordinarily circulate in the blood."The PSA test can detect high levels of PSA that may indicate the presence of prostate cancer," the clinic states on its website. "However, many other conditions, such as an enlarged or inflamed prostate, also can increase PSA levels. Therefore, determining what a high PSA score means can be complicated."NEW PROSTATE CANCER TEST PINPOINTS DISEASE BETTER THAN PSA OPTION, STUDY FINDSThe former presidents prostate cancer has been characterized by a Gleason score of 9 (grade group 5) with "metastasis to the bone." The ranking of Biden's cancer on the Gleason scale, a grading system for prostate cancer severity, has sparked concerns, as it correlates with high-grade cancer.The fact that Bidens cancer has been classified as "hormone-sensitive" means it could be more responsive to hormone therapies, and thus more treatable.Biden's prostate cancer diagnosis has ignited several questions about why it wasn't caught sooner, despite undergoing several physical examinations."There are things going on that the public wasn't informed of," President Donald Trump said Monday. "I think somebody's going to have to speak to his doctor.""This is no longer politically correct. This is dangerous for our country," he added. "Somebody is not telling the facts."