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The 100-day PSA: usefulness as surrogate end point for biochemical disease-free survival after definitive radiotherapy of prostate cancer.

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  • 1Naval Medical Center, San Diego, California, USA.


Overall and biochemical disease-free (bNED) survival data after definitive radiotherapy (RT) for prostate cancer (CaP) requires decades of patient follow-up. Surrogates involving dynamics of prostate-specific antigen (PSA) decline, PSA nadir and time thereto have been unrewarding. This study investigated the metric of the PSA value 100 days after RT (PSA(100)), analyzed with respect to 8-y bNED survival. A total of 214 patients with T1-3 CaP were treated with definitive RT (defined as dose >66 Gy) in our institution between 1/1/1988 and 12/31/2000. All were subject to continuous follow-up with routine PSA levels. Biochemical failure (77 patients) was defined by the ASTRO criteria (n=67) or by the date of first hormonal therapy for a rising PSA, which did not meet the ASTRO criteria (n=10). No patients were included if they received postoperative radiation, or if hormones were administered prior to bNED recurrence, if any. Patients were stratified by PSA(100) values </= or >4.0 ng/ml, and </= or <2.5 ng/ml. Median follow-up was 64.3 months: follow-up data were calculated as of time to last PSA, with data collection as of 12/31/02. Patients with PSA(100)</=4.0 ng/ml had 62% 8-y bNED survival, and those with PSA(100)>4.0 ng/ml had 20% 8-y bNED survival (P<0.001). Use of a PSA(100) cutoff of 2.5 ng/ml yielded no significant difference in 8-y bNED survival (P=0.229). Cox proportional analysis revealed that initial PSA (P=0.006), stage (P=0.001) and PSA(100)</=4.0 ng/ml (P=0.002) were significantly related to bNED survival, but that age (P=0.887), race (P=0.500), RT dose (P=0.669), Gleason sum (P=0.091), and PSA(100)</=2.5 ng/ml (P=0.128) were not. In conclusion, PSA(100) using a cutoff of 4 ng/ml is a valuable and reliable surrogate for bNED survival after definitive RT, requiring less follow-up than other metrics. Patients with less values will have only about a 1 in 3 chance of bNED failure at 8 y.

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