Purpose: We validated our ultrasensitive prostate specific antigen (PSA) assay based on lyophilization and 4-fold concentration of patient sera with the clinical long-term followup and according to histopathological characteristics of 422 patients treated with radical retropubic prostatectomy for prostate cancer.
Materials and methods: Each serum sample was divided into 2 aliquots for standard and 4-fold concentrated (ultrasensitive) detection. Samples were analyzed by the same unmodified DPC-Immulite PSA assay. Biochemical relapse was defined as an increase of at least 0.10 ng./ml. in native serum (equivalent to 0.025 ng./ml. in concentrated serum). Mean followup was 449 days (range 29 to 2,057). Kaplan-Meier analysis of standard and ultrasensitive detection results was done, and findings were correlated with pathological stage, Gleason grade, total cancer volume, Gleason grade 4 cancer volume and margin status. Significance of earlier detection in ultrasensitive versus standard detection was calculated with the log rank (Mantel-Cox) test with p <0.05 considered significant.
Results: Of 442 patients 88 (20.8%) experienced biochemical recurrence. Of this cohort 28 (31%) demonstrated early failure on the ultrasensitive assay which was later confirmed on the standard assay, 37 (42%) had failure simultaneously on both assays and 23 (26%) had failure on the ultrasensitive but remained disease-free on the standard assay. Average time for ultrasensitive assay detection of recurrence was 288 days (standard 555). Kaplan-Meier analysis revealed significant advantages in earlier detection of recurrence with the ultrasensitive assay, and close correlation with pathological stage, Gleason grade, margin status and Gleason grade 4 cancer volume. Time advantages of ultrasensitive versus standard detection were greater for advanced cancers (pT3a/b or greater, Gleason 3 + 4 or greater) than for small, low grade tumors. All patients who had positive results on the standard assay had a previous (28) or simultaneous (37) positive ultrasensitive result. With standard detection 25% of all relapses were evident within the first year of surgery and with ultrasensitive detection the percentage increased to 85.7%. On both assays 334 patients remained free of biochemical recurrence.
Conclusions: Our ultrasensitive PSA assay is useful for early detection of biochemical relapse after radical retropubic prostatectomy. It not only provides the same accuracy as conventional PSA assays but also offers the advantage of detecting recurrence about 300 days earlier. Thus, long-term results of radical retropubic prostatectomy series can be calculated sooner. The clinical impact of this assay will be obvious once curative treatment options are available if applied at the earliest time of evident tumor recurrence.