Abstract:Purpose/Objective: Determination of overall survival after definitive radiotherapy (RT) for prostate cancer (CaP) may require decades of patient follow-up; robust biochemical (bNED) survival data require follow-up exceeding 5 years. Surrogates of bNED survival involving dynamics of prostate specific antigen (PSA) decline and time to nadir have been unrewarding. Use of PSA nadir as surrogate is subject to numerous biases and requires several PSA levels over several years post-radiotherapy. This study investigated the metric of the PSA value 100 days after RT (PSA100), analyzed with respect to 8-year bNED survival. Materials/Methods: 214 patients with T1-3 CaP were treated with definitive RT (defined as RT dose of 66 Gy or greater) in our institution between 1/1/1988 and 12/31/2000 . All patients were subject to continuous follow-up with routine PSA levels. Biochemical failure was defined by the ASTRO criteria (n=67), or by the date of first hormonal therapy for a rising PSA not meeting the ASTRO criteria (n=10). No patients were included if treated post-operatively or with adjuvant hormonal therapy. Patients were stratified by PSA100 values less than/equal to vs. greater than 4.0 ng/ml, and less than/equal to vs. greater than 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. Results: Patients with PSA100 less than/equal to 4.0 ng/ml had 62% 8-year bNED survival, and with PSA100 greater than 4.0 ng/ml had 20% 8-year bNED survival (p<0.001; see Figure). Using a PSA100 cutoff of 2.5 ng/ml yielded no significant difference in 8-year bNED survival (p=0.229)(Figure not shown). Multivariate analysis revealed that initial PSA (p=0.033), stage (p=0.005), RT dose (p=0.029), and PSA100 less than/equal to 4.0 ng/ml (p=0.003) were significantly related to bNED survival, but that age (p=0.641), race (Fishers exact p=0.220), Gleason sum (p=0.294), and PSA100 less than/equal to 2.5 ng/ml (p=0.066) were not. Conclusions: PSA100 using a cutoff of 4 ng/ml is a reliable surrogate for bNED survival after definitive RT, requiring less follow-up time and visits than other metrics. Patients with values less than 4.0 ng/ml will have only about a 1 in 3 chance of bNED failure at 8 years; a case may be made for infrequent follow-up in such cases. Patients with values greater will have an 80% likelihood of bNED failure at 8 years, and require closer follow-up. Patients should have routine PSA draws about 100 days post-RT, with subsequent follow-up tailored to that result.
Johnstone MD, MA, P,
The 100-Day PSA: Usefulness as Prognostic Factor for Biochemical Disease-free Survival after Definitive Radiotherapy of Prostate Cancer. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3239417.html
