It may be that we need to rethink “undetectable.” After radical prostatectomy, we all focus on the number 0.1 ng/ml — that’s undetectable PSA. But recent advances in technology have made it possible to measure PSA at much lower levels. Is it good? Alan W. Partin, M.D., Ph.D., The David Hall McConnell Professor of Urology and Director of the Brady, thinks the answer may turn out to be yes.
Partin, Daniel W. Chan, Ph.D., and Lori Sokoll, Ph.D., have been working with a company called Quanterix, in collaboration with New York University urologist Herb Lepor (formerly at Hopkins) to see how well a new, ultrasensitive PSA assay works. “The test, AccuPSA, can accurately measure PSA values at 1,000 times lower than the standard assays we use today,” says Partin. In a study to be published in the British Journal of Urology International, Partin and colleagues examined blood samples from 31 men whose PSA had been undetectable for at least fi ve years after radical prostatectomy. “All of the men had PSA lower than 0.1 ng/ml after surgery, yet one-third of them later had biochemical recurrence, while the others kept having undetectable PSA for many years after surgery.” The men were similar in age, race, and had negative surgical margins after surgery; however, the men whose PSA levels went up had a higher pre-surgical PSA, clinical and pathological stage, and Gleason grade than the men whose levels remained very low.
When the investigators tested the samples with AccuPSA, they found that at three months after surgery, all of the men who ultimately had a rise in PSA had an AccuPSA level of 0.003 ng/ml or greater, “a number that, by standard measures, we would have considered to be really good — undetectable,” notes Partin. But among the men whose PSA never went back up, 75 percent had AccuPSA levels lower than 0.003 ng/ml.
This was a small, pilot study, and larger tests are needed to confirm these findings. However, says Partin, “these results suggest that men could have an AccuPSA test at three months after surgery, and if the level is lower than 0.003 ng/ml, they could be better reassured that all of their cancer has been removed. On the other hand, if a man’s level is higher than 0.003 ng/ml, he might be monitored more closely for PSA recurrence in the immediate years after his surgery.