Controversy on the clinical role for ultrasensitive PSA assays
Controversy on the clinical role for ultrasensitive PSA assays
Ultrasensitive assays have been introduced for prostate-specific antigen (PSA), but the utility of these assays is not well defined. The major application of PSA measurement is as a screening test for prostate cancer in men aged 50 years and older. In this application, a result above a cutoff of about 4.0 ng/mL (which may be adjusted for patient age or other factors) is regarded as positive, warranting further testing. The first generation of commercial PSA assays is generally sensitive enough (analytically) to adequately distinguish the elevated levels from normal.
Some studies have shown that more sensitive assays can detect “biochemical relapse” of prostate cancer earlier, by months or years, compared to less sensitive assays.1,2 However, none of these assays have Food and Drug Administration-approved performance claims for early detection of prostate cancer recurrence after radical prostatectomy. A compelling clinical application of high-sensitivity PSA assays has not been established. This is largely because the prognostic and therapeutic implications of biochemical relapse are unclear. Published studies have shown that on average biochemical relapse precedes clinical relapse, and that biochemical relapse is detected earlier by highly sensitive assays. In an individual patient, however, PSA may be measurably increasing for years before the advent of any clinical problem, and, in some cases, the PSA concentrations spontaneously decrease.
The level of 0.2 ng/mL has been proposed as the threshold for defining “biochemical tumor recurrence.”3 Many of the current PSA assays cannot reliably measure specimens at this level.4 Even when the analytic measurements are accurate, the biologic variation of the measurements is significant. If 0.2 ng/mL is taken as the critical PSA value to signal tumor recurrence in a post-radical prostatectomy man, that patient could be classified as having PSA values “consistent with tumor recurrence” when he actually does not have new tumor growth. Perhaps this is part of the reason some investigators recommend setting the threshold for biochemical recurrence at 0.4 ng/mL.5 Overall, there still are a lot of questions regarding the clinical role of “ultrasensitive” PSA assays.
References
1J Urol. 1997;157:1322-1328.
2J Urol. 1999;161:1206-1211
3J Urol. 2002;167:1310-1313
4Arch Pathol Lab Med. 2004;128:341-343
5J Urol. 2001;165:1146-1151
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