Detection of residual prostate cancer after radical prostatectomy with the Abbott IMx PSA assay.

OBJECTIVES: This analysis was performed to define the level of serum prostate-specific antigen (PSA) measured with the Abbott IMx assay that indicates residual or progressive prostate cancer after radical retropubic prostatectomy (RRP). METHODS: Since March 1992, we have used the Abbott IMx assay to determine PSA levels. Between March 1992 and June 1994, 102 of those patients having RRPs were found to have pathologic Stage C prostate cancer. Fifty-one of these patients had at least one serum PSA measurement of 0.1 ng/mL or greater. Eight patients were excluded from the analysis because they received postoperative radiotherapy that might have influenced subsequent PSA levels. The remaining 43 patients are the subjects of this analysis and were evaluated to determine the "clinical threshold" or minimal serum PSA level after RRP indicative of progressive disease. Patients were followed for 6 to 36 months (median 23 months) from the date of the RRP. Failure was defined as a subsequent increase of PSA to greater than 0.3 ng/mL. Freedom from failure was determined using the Kaplan-Meier product limit method. RESULTS: Of the patients with at least one postoperative serum PSA level of 0.1 ng/mL, the subsequent freedom from failure was 80% at 23 months as compared with 13% in patients with at least one postoperative PSA level of 0.2 ng/mL (P = 0.003). CONCLUSIONS: Following RRP for pathologic Stage C prostate cancer, a solitary PSA level of 0.1 ng/mL (measured with the IMx assay) was followed by a progressive rise in PSA levels in only a minority of patients within the first 2 years after surgery. In contrast, the majority of patients with a postoperative PSA level of 0.2 ng/mL subsequently had progressively rising PSA levels. This indicates that a serum PSA level of 0.2 ng/mL is reflective of residual prostate cancer.