Post-treatment prostate biopsies in the era of three-dimensional conformal radiotherapy: what can they teach us?

BACKGROUND: The ability to discriminate between therapeutic success and failure after radiotherapy (RT) for prostate cancer (PCa) remains a clinical challenge. Post-treatment biopsies would seem ideal for evaluating innovations such as dose escalation protocols or combination treatments involving brachytherapy or hormones.

OBJECTIVE: Correlate post-treatment biopsy results with prostate-specific antigen (PSA) and clinical outcome in PCa patients treated with three-dimensional conformal radiotherapy (3DCRT) in a dose-escalation study.

DESIGN, SETTING, AND PARTICIPANTS: This study included 160 patients with clinical stage T1c to T3b PCa treated between 1995 and 2005 in Hospital Universitario la Princesa with 3DCRT who consented to and underwent a transrectal ultrasound (TRUS)-guided prostate biopsy 24-36 mo after RT. The median follow-up was 78 mo (range 27-171 mo).

INTERVENTION: The median radiation dose was 74 gray (Gy; range 66.0-84.1). Risk-adapted short-term androgen deprivation (STAD) and long-term androgen deprivation (LTAD) were associated in 25 and 106 patients, respectively. Right and left systematic biopsies were carried out by the same urologist and were examined by a genitourinary pathologist.

MEASUREMENTS: Biochemical disease-free survival (bDFS) according to American Society for Therapeutic Radiology and Oncology (ASTRO) 1997 and Phoenix definition criteria as well as histologic control using post-treatment prostate biopsies.

RESULTS: Twenty-one percent of patients (34 of 160) had post-treatment-positive biopsies (PB). The 5-yr bDFS according to the Phoenix definition was 87%, 65%, and 92% for the whole series (PB and negative biopsies [NB] patients, respectively [p<0.001]). Multivariate analysis showed that biopsy status at 24-36 mo was an independent predictor of bDFS (p<0.0005) and of clinical failure-free survival (p=0.043).

CONCLUSION: The results of the present study show a strong correlation between a post-treatment PB and the 5-yr probability of bDFS, confirming that PSA control can be an adequate surrogate for local control, as assessed by post-treatment biopsies.