Validation of the prognostic ability of the five-tiered ISUP grade groups for prostate cancer treated with definitive dose-escalated external beam radiation treatment in a contemporary Australian population

Abstract

Purpose: To validate the prognostic ability of ISUP grade groups¹ for predicting biochemical failure in patients treated with definitive external beam radiation treatment (EBRT) for prostate cancer in a contemporary Australian setting. Methods and Materials: Patients were treated with image-guided, dose-escalated EBRT between 2005 and 2016 at 4 institutions (Northern Sydney Cancer Centre, Central Coast Cancer Centre, North Coast Cancer Institute and Mid North Coast Cancer Institute). Primary outcome was biochemical failure defined as nadir + 2 ng/ml from the date of treatment. Kaplan-Meier estimates adjusted for competing risk of death were calculated for patients according to ISUP grade group. Result(s): 2525 patients were included, their T stages were 1, 2 and 3; in 30%, 49% and 19% of men. Median age, initial PSA and follow-up were 72 years, 9.4 ng/ml, and 5.8 years, respectively. There were 6.8% ISUP grade group 1, and 29.8%, 25.3%, 17.0% and 21.1% grade group 2-5 patients. androgen deprivation (AD) was used in 82% of men; of whom 44% received long-term (>9 months) AD and 38% received short-term (<9 months) AD. The risk of biochemical failure was HR 1.03, HR 1.32, HR 1.28 and HR 2.83 for ISUP grade groups 2-5 relative to group 1. There was greater differentiation between ISUP grade groups in men treated without AD compared to those who received any AD. Our data support 3 distinct risk groups with similar risk of biochemical failure for ISUP grade groups 1 and 2, followed by groups 3 and 4, followed by group 5. Conclusion(s): The five-tiered ISUP grade group stratification does not reflect five distinct prognostic groups in a large contemporary cohort of dose-escalated Australian patients. Following Australian eviQ radiotherapy guidelines, ISUP grade groups are not valid. We propose further work is required to validate risk groupings for patients treated using modern radiation techniques.