Overtreatment of a Patient With Presumed Recurrent Prostate Cancer Based on False-Positive Prostate Specific Antigen Results

Abstract

A 59-year-old man underwent radical prostatectomy for clinical stage T1c prostate adenocarcinoma. Serum PSA at diagnosis was 8.5 ng/ml. Pathological stage was T3bN0 with evidence of bilateral Gleason 4 3 7 cancer, extracapsular extension, positive margins and bilateral seminal vesicle involvement. Following surgery the patient received adjuvant radiation therapy to the prostate bed. Postoperatively, PSA was undetectable. Nine months following surgery PSA measured 0.02 ng/ml on the Access Hybritech free PSA assay (Beckman Coulter, Inc., Fullerton, California). Within 3 weeks PSA measured 37 ng/ml on the AxSYM assay. Repeat AxSYM assay PSA measurement 2 weeks later was 31.3 ng/ml. Evaluation, including bone scan and abdominal computerized tomography, was negative for metastatic disease. Therapy was initiated with 10.8 mg goserelin depot injection and 50 mg bicalutamide daily. Three weeks after initiation of hormonal therapy PSA measured 0.02 ng/ml by Hybritech but 6 weeks later measured 28.2 ng/ml by AxSYM. Because of this discrepancy, repeat PSAs were measured within 3 days of each other using the different assays, and results varied significantly with the PSA measuring less than 0.01 ng/ml on the Hybritech assay but 23.6 ng/ml on the AxSYM assay (see figure). Serum PSA was measured using the AxSYM assay with and without heterophilic blocking reagent pretreatment (Scantibodies Laboratory, Santee, California).1 No difference was detected in these two measurements, ruling out the presence of a heterophilic antibody. Hormonal therapy was stopped. Eight months after the last goserelin injection PSA was undetectable on both assays.