Top Line: Everyone knows the classic distinction between grade group 2 (3+4=7) and grade group 3 (4+3=7) intermediate risk (IR) prostate cancer, but this crude metric has its limitations.
The Study: For one thing, it’s a proportional rather than absolute descriptor. For example, Joe Bloe could have a greater absolute volume of Gleason 4 disease than Joe Schmoe yet have an even greater amount of Gleason 3 disease, leading Bloe to be GG2 while Schmoe is GG3. Here’s a Torontonian single institution look at >400 men following definitive radiation with HDR brachy boost for IR prostate cancer. Of note, only 17% (n=71) received ADT. Outcomes are stratified by absolute percentage of Gleason pattern 4 (APP4) among diagnostic 12-core biopsies. Note: APP4 = percentage of cores with disease x percentage of disease that is pattern 4. For instance, if 4 of 12 cores demonstrate cancer and 2 cores have 30% and 20% Gleason 4, then the APP4 = (4/12) x [(.30 + .20) / 4) = 4.1%. As might be expected at a median follow-up just over 5 years, nearly 10% (n=38) had a biochemical failure and just 2% (n=8) developed distant disease. As hypothesized, APP4 was predictive of both endpoints with an optimal dichotomous cut-off of >3.3% as an indicator of early biochemical recurrence (HR 4) and of >17.5% for early development of metastatic disease (HR 26).
Bottom Line: Absolute amount of Glease 4 disease can effectively stratify IR prostate cancer. | Martell, Radiother Oncol 2019


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