Prostate-Specific Antigen 5 Years following Stereotactic Body Radiation Therapy for Low- and Intermediate-Risk Prostate Cancer: An Ablative Procedure?

In 1996 the American Society for Therapeutic Radiology and Oncology (ASTRO) sponsored a Consensus Conference to establish a definition of biochemical failure after external beam radiotherapy (EBRT). The ASTRO definition defined prostate specific antigen (PSA) failure as occurring after three consecutive PSA rises after a nadir with the date of failure as the point halfway between the nadir date and the first rise or any rise great enough to provoke initiation of therapy. This definition was not linked to clinical progression or survival; it performed poorly in patients undergoing hormonal therapy (HT), and backdating biased the Kaplan-Meier estimates of event-free survival. A second Consensus Conference was sponsored by ASTRO and the Radiation Therapy Oncology Group in Phoenix, Arizona, on January 21, 2005, to revise the ASTRO definition. The panel recommended: (1) a rise by 2 ng/mL or more above the nadir PSA be considered the standard definition for biochemical failure after EBRT with or without HT; (2) the date of failure be determined "at call" (not backdated). They recommended that investigators be allowed to use the ASTRO Consensus Definition after EBRT alone (no hormonal therapy) with strict adherence to guidelines as to "adequate follow-up." To avoid the artifacts resulting from short follow-up, the reported date of control should be listed as 2 years short of the median follow-up. For example, if the median follow-up is 5 years, control rates at 3 years should be cited. Retaining a strict version of the ASTRO definition would allow comparisons with a large existing body of literature.

Prostate-specific antigen (PSA) defined biochemical recurrence (BCR) of prostate cancer is widely used for reporting the outcome of radical prostatectomy (RP). A standardized BCR definition is lacking, and overall progression-free probability and risk of subsequent metastatic disease progression may vary greatly depending on the PSA criterion used. Ten definitions of BCR were evaluated to identify the one that best explains metastatic progression. Of 3,125 patients who underwent RP at our institution since 1985, 75 developed distant metastasis during a median follow-up of 49 months. To predict metastasis progression, we modeled the clinical information using multivariable Cox regression analysis. BCR was included in the model as a time-dependent covariate, and separate models were developed for each definition. A goodness-of-fit (R2) statistic was used to determine the Cox model (and thereby the BCR definition) that best explained metastatic progression. The 10-year progression-free probability ranged from 63% to 79%, depending on the BCR definition. The model containing BCR defined as a PSA of at least 0.4 ng/mL followed by another increase best explained metastatic progression (R2 = 0.21). This definition was also associated with a high probability of subsequent secondary therapy, continued PSA progression, and rapid PSA doubling time. BCR defined as a PSA value of at least 0.4 ng/mL followed by another increase best explains the development of distant metastasis among 10 candidate definitions, after controlling for clinical variables and the use of secondary therapy. On the basis of this evidence, we propose that this definition be adopted as the standard for reporting the outcome of RP.