The clinical significance of persistent cancer cells on prostate biopsy after high-dose-rate brachytherapy boost for intermediate-risk prostate cancer

PURPOSE: To evaluate the association between post-treatment biopsy results and the probability of biochemical disease-free survival (bDFS). METHODS AND MATERIALS: Two sequential prospective clinical trials were undertaken in men with intermediate-risk prostate cancer (T1-T2 with either Gleason score 7 and prostate-specific antigen [PSA] level lower than 20 ng/mL or Gleason score 6 and PSA level of 10-20 ng/mL). All patients had high-dose-rate brachytherapy (two fractions of 10 Gy separated by 1 week or a single 15-Gy fraction) followed by external beam radiotherapy. Both study groups were followed prospectively with regular PSA readings and prostate biopsy at 2 years. Biopsies were reported as: positive = malignant cells with no or only partial radiation effect, negative = no malignant cells seen, and indeterminate = malignant cells with marked radiation effect. Biochemical failure was defined using the nadir +2 ng/mL definition and estimated using the Kaplan-Meier curves. Fisher exact test was performed to investigate any relationships between high-dose-rate treatment and biopsy results. RESULTS: A total of 181 patients were included in this analysis. The median followup for all patients was 6.2 years (range, 0.3-10.5). Post-treatment biopsy was performed in 111 patients of which 82 (74%) were negative, 17 (15%) indeterminate, and 12 (11%) malignant. The 5-year bDFS was 97.5%, 93.8%, and 83.3% for those with benign, indeterminate, and malignant biopsies, respectively (p = 0.4398). Median PSA nadir was 0.08 ng/mL (range, 0.01-3.63), with no difference in PSA change over time by treatment (p = 0.9953) or biopsy result (p = 0.4398) CONCLUSIONS: Routine biopsy at 2 years was not able to reliably predict which patients would ultimately fail as even those with a positive biopsy had a long-term bDFS higher than 80%. (C) 2015 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.