EAU 2017: How to define ‘significant’ disease on targeted biopsy

London, England (UroToday.com) At this morning’s EAU 2017 “How to get the most out of prostate cancer imaging”, Dr. Hashim Ahmed provided a detailed discussion how to define significant disease on targeted biopsy. As a leader in the field of MRI-guided targeted biopsy, Dr. Ahmed’s presentation was highly anticipated.

Dr. Ahmed caught the attention of the audience with his opening remarks “our current definitions of significant disease are based on TRUS biopsy and a TRUS biopsy without a pre-biopsy MRI is a flawed approach. We must do away with Epstein, D’Amico and NCCN risk stratification and start again.” With sophisticated figures to illustrate his point, Dr. Ahmed made the case that TRUS biopsy may underestimate disease histology (understage Gleason score), as well as extent of disease (% core positive) compared to image-guided biopsy. Highlighting work from his institution, Dr. Ahmed noted that 12-core TRUS biopsy classified only 24% of clinically significant prostate cancer compared to 74% of cases using four targeted cores. Specifically, for 12-core TRUS biopsy diagnosed Gleason score 7 disease (both 3+4 and 4+3), MRI-guided targeted biopsy will upstage a number of patients to higher-risk disease.

Characterizing significant disease on targeted biopsy is not straight-forward according to Dr. Ahmed. Some have advocated that any absence of Gleason 4 disease is clinically insignificant disease. In a study from four US centers of 14,123 patients undergoing radical prostatectomy with lymphadenectomy (1975-2010), 22 patients had lymph node metastasis [1]. Of the 19 specimens available for review using contemporary Gleason staging guidelines, all patients were upgraded to a percentage of Gleason pattern 4 (thus, not true Gleason 6). Furthermore, Dr. Ahmed highlights that there is heterogeneity as to how risk stratification algorithms characterize significant disease regarding tumor volume and length of cancer core on biopsy.

Dr. Ahmed and his group have proposed that based on template prostate mapping biopsies at their institution, clinically insignificant cancer must fit the following criteria: total cancer core length ≤5 mm, longest cancer core length ≤3 mm, and Gleason score ≤3+3 disease. Although as Dr. Ahmed points out, this system is not without flaws. He concluded that the current definition for clinically significant prostate cancer are inaccurate and are too conservative, as highlighted by the MRI-grade shift particularly for Gleason 7 disease. As a final word of caution, Dr. Ahmed notes that this risk inflation from targeted biopsies may result in over-treatment if we apply the results to the current risk models.

1. Ross HM, Kryvenko ON, Cowan, et al. Do adenocarcinomas of the prostate with Gleason score (GS) ≤6 have the potential to metastasize to lymph nodes? Am J Surg Pathol 2012;36(9):1346-1352.

Presented by: Hashim U. Ahmed, Imperial College London, London, UK

Written by: Zachary Klaassen, MD, Urologic Oncology Fellow, University of Toronto
Twitter: @zklaassen_md

at the #EAU17 -March 24-28, 2017- London, England