As enzymes go, PSA is kind of a tough guy. Like a feisty slugger always looking for a fight, it actively attacks proteins at every opportunity. In the bloodstream, however, PSA is usually restrained by inhibitors that prevent it from breaking down proteins; like a member of a chain gang, it is tied up, or bound.

In one promising new area of research, scientists are working to characterize the forms of PSA in the bloodstream. Is the PSA bound to the inhibitors, or is it on the loose—is it free? Currently, the tests doctors use to measure PSA detect both the bound and unbound molecules. But it might be helpful if we could tell which was which; new evidence indicates that the amount of bound PSA in the blood may be higher in men with prostate cancer than in men with BPH. If this proves to be true, one day soon it may be possible to distinguish between the PSA arising from prostate cancer and the PSA arising from BPH by measuring both its bound and free forms.

In the future, we’ll see a new, more specific generation of PSA assays, tests capable of quantifying different forms of the molecule in the bloodstream. Such tests may provide useful clinical information, not only for diagnosis of prostate cancer, but also for evaluation and follow-up.


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