PSA Worthless for Prostate Cancer Screening?
'PSA Era Over,' Test's Pioneer Now Says
20 Years and 1,317 Prostates continued...
In prostates removed during the earliest five years of the study, PSA levels predicted cancer severity. That is, the higher the patient's PSA, the larger and more aggressive the patient's prostate cancer.
But in the last five years of the study, PSA levels had little if anything to do with cancer severity. All PSA levels predicted, Stamey and colleagues found, was an enlarged prostate -- and all men's prostates enlarge as they age.
"In the first five years, we had a correlation of 60% between high PSA levels and severe cancer -- so the PSA test wasn't perfect even in the early years," Stamey say. "But my paper shows it is a straight curve down to a 2% correlation in the last five years. We show PSA is driven by benign enlargement of the prostate."
What's going on? Urologist H. Ballentine Carter, MD, a researcher at the Johns Hopkins Brady Urological Institute in Baltimore, explains.
"At the beginning of the PSA era, we were pulling out of the population patients with larger tumors, where there was better correlation between PSA and cancer volume," Carter tells WebMD. "Dr. Stamey's contention is that as the PSA era has gone on, we have culled those large tumors. Now we are detecting very, very small tumors where there is less correlation between PSA and cancer."