The PSA Blood Test
PSA plays a variety of roles, the most familiar being screening to detect prostate cancer at an early stage. PSA also helps to define the Stages of Blue. Another role of PSA is to detect cancer relapse after surgery or radiation. Lastly, rises or declines in PSA after hormone therapy or chemotherapy help determine whether a treatment is working.
Prostate Cancer Screening is Controversial
PSA screening often leads to the detection of small, essentially harmless cancers. However, doctors and patients frequently overreact, rushing into unnecessary radical treatment. Over treatment of tiny cancers became such a big problem that in 2011 a government-sponsored team of experts, the U.S. Preventative Services Task Force, issued a warning against routine PSA screening. This recommendation was recently modified, acknowledging the possible value of PSA screening in well-informed patients.
Scans Measure the Size of the Prostate
Imaging with ultrasound or MRI improves the accuracy of PSA. Many men run high PSA levels from a condition called BPH that is totally unrelated to cancer. BPH is benign enlargement of the prostate gland, a common phenomenon associated with aging. The main issue is that PSA increases as the gland enlarges, but this rise in PSA has nothing to do with cancer.
There is a specific method for determining when the PSA is elevated higher than what would be expected for an enlarged prostate. It works by determining the prostate size in cubic centimeters(cc) using imaging and dividing the size by 10. For example, a noncancerous 30cc prostate should have a PSA of around 3.0; for a noncancerous 50cc prostate the PSA should be around 5.0. A man’s PSA with a 100cc prostate will be approximately 10. PSA is only abnormal (the official term is a “high PSA density”) when it’s 50 percent higher than would be expected, based on the prostate’s size. For example, a man’s PSA is abnormal if he has a 30cc prostate and his PSA is above 4.5. An abnormal PSA for a 50cc prostate is above 7.5. For a 100cc gland, PSA would need to be above 15 to be suspicious.
PSA Density
Doctors use a less intuitive way to determine when the PSA is higher than what can be attributed to an enlarged prostate. The net effect, however, is the same. Instead of dividing PSA into the gland volume, they do the opposite. They divide the gland volume into the PSA. Using this inverted formula, an abnormal PSA relative to a specific-sized prostate is anything above 0.15. Men above 0.15, using this formula, are said to have a high “PSA Density.”
A Suggested PSA Screening Protocol
It’s reasonable to start checking PSA yearly in men over the age of 45. Men with a family history of prostate cancer or men who are African-American should start annual testing at age 40. Men over age 75 who are in good health should continue screening.
Using PSA to Stage Prostate Cancer
Despite the controversies that surround the use of PSA for screening, there are no controversies about using PSA for cancer staging. Men with a higher PSA at the time of diagnosis, above 10 or 20 for example, are more likely to have cancer that has spread outside the gland.
PSA to Monitor for Cancer Relapse After Surgery or Radiation
Cancer recurrence is signaled by a rising PSA. Normally after surgery, the PSA should drop to undetectable levels. Even a small rise in PSA is significant. After radiation, the PSA should generally remain under 1.0, though exceptions certainly exist. The rate of PSA doubling is a very important indicator of the recurrent cancer’s aggressiveness. For example, recurrences associated with PSA levels that require over 12 months to double are low-grade. On the other hand, PSA that doubles in less than three months signals aggressive disease.
Determining the Response to Hormone Therapy or Chemotherapy
A PSA decline of more than 30 percent within a couple of months of starting chemotherapy provides a strong indication that the treatment is working. However, not every treatment, even when it is effective, makes an impact on PSA. Two new therapies for Royal—Xofigo and Provenge—clearly prolong life but may show little or no impact on PSA.
Conclusion
PSA results must be interpreted in the context of each patient’s overall circumstances by an expert with experience in managing prostate cancer. Unexpected PSA results should always be retested. Laboratory errors are possible and variations also occur between labs.
Stanley Brosman, MD is board-certified in urology. Former chief of urology at UCLA/Harbor General Hospital, a clinical professor of surgery/urology at UCLA,. and associate director of urologic oncology at John Wayne Cancer Institute. He is past president of the urology section of the California Medical Society and past president of the Los Angeles Urologic Society. He is author or coauthor of more than 80 peer-reviewed scientific articles and over 50 book chapters or monographs. He practices urology with a focus on prostate cancer in Santa Monica, California, at the Pacific Urology Institute.