Prostate Specific Antigen Doubling Time Subsequent to Radical Prostatectomy as a Prognosticator of Outcome Following Salvage Radiotherapy

PURPOSE: Therapy for men with detectable prostate specific antigen (PSA) following radical prostatectomy (RP) for prostate cancer remains controversial. Salvage radiotherapy (SRT) is commonly used because of its relatively low morbidity. We present a single institution retrospective review of patients treated with SRT. MATERIALS AND METHODS: A longitudinal cohort study (between April 1987 and April 2000) using the referral based Mayo Clinic Prostate Cancer Registry was conducted. A total of 211 patients were included in this study if detectable serum PSA was the sole indication for SRT and no hormonal therapy was administered. RESULTS: Median followup from surgery to death or last followup was 7.2 years, from RP to SRT was 1.7 years and from SRT to last contact was 4.2 years. Median PSA and prostate specific antigen doubling time (PSADT) at SRT initiation was 0.60 ng/ml and 7.32 months; respectively. Of the patients 90% had nadir PSA less than 0.4 ng/ml within 3 years of SRT. Biochemical disease-free rates at 5 years for PSADT less than 12 or 12 months or greater was 48% and 66%; respectively (p = 0.080). By 10 years there was no significant difference in biochemical disease-free rate (34% vs 35%). Clinical metastasis (10% and 29%) developed in patients with a PSADT less than 12 months at a significantly higher rate than in patients with a PSADT of 12 months or more (0% and 17%, p = 0.045) at 5 and 10 years, respectively. Multivariate analysis revealed pre-SRT PSADT (less than 12 months, H.R. 3.88, p = 0.032), seminal vesicle invasion (H.R. 3.22, p = 0.008), pathological grade (H.R. 1.58, p = 0.023) and PSA at SRT (H.R. 1.29 for a 2-fold increase, p = 0.044) to be significant independent predictors of clinical recurrence. The interval from RP to SRT did not add to the model (p = 0.22). CONCLUSIONS: A biochemical response can be expected in the majority of patients within 3 years of receiving SRT. Patients with a pre-SRT PSADT of 1 year or less have a less sustained biochemical response to SRT than patients with a PSADT greater than 1, yet the majority of patients appear to receive long-term benefit from this adjunctive therapy. PSADT is an independent predictor of biochemical and clinical disease recurrence following SRT.