Data just published in Nature Biotechnology suggests that a new type of PSA test developed by a company called Quanterix is 1,700 times more sensitive than older, standard PSA detection methods used in clinical laboratories.
Standard PSA tests can measure with accuracy down to about 0.1 ng/ml. Ultrasensitive PSA tests can measure levels accurately to about 0.003 ng/ml. The new Quanterix test appears to be able to measure PSA with accuracy down to 14 fg/ml (femtograms per milliliter), which is equivalent to 0.000014 ng/ml, making it about 200 times more sensitive than the current ultrasensitive PSA tests.
Rissin et al. found that the new Quanterix assay was able to detect these extraordinarily small levels of PSA in the blood of some men who had had a prior radical prostatectomy (RP) when commercial assays were unable to detect any PSA. However, there is going to be a great deal more work necessary before we can validate the real utility of a test this sensitive.
The “New” Prostate Cancer InfoLink can see a potential value for this test in the detection of a rising PSA as early as possible in men known to be at very high risk for disease progression after an RP, but even then it may be the rate of rise of PSA levels this low that is more clinically significant than any absolute value.
There are very real potential problems with a test this sensitive. It would have minimal value prior to treatment because it is certainly too sensitive for use in that setting. Equally, since PSA levels almost never go to levels below 0.05 ng/ml after any form of treatment except RP, its potential in measuring progression after such treatments may be very small too. Most importantly, there are still serious questions about the clinical significance of small changes in PSA levels at a particular point in time.
For those who are interested in finding out more about this test, we refer to a commentary on the MIT Technology Review web site and to additional information available from Quanterix.
We should point out that this test is only one among many “ultra-ultasensitive” PSA tests now in development. As just one example, there was another announcement yesterday about a nanotechnology-based PSA test in development by a company called VeriSens. This test is supposedly about 300 times more sensitive than current standard PSA tests. Reuters carried a commentary on this piece of news.