Assessing the oncologic risk when systematic and multiparametric magnetic resonance imaging-targeted prostate biopsy grade groups are discordant

Background In the systematic biopsy era, prostate biopsy grading followed the rule that the International Society of Urological Pathology grade group assigned was the highest grade group of any core. This rule has been retained in the era of multiparametric magnetic resonance imaging (MRI)-guided biopsy in the case of discordance between systematic biopsy and targeted biopsy samples. We assessed whether oncologic risk in patients undergoing systematic biopsy and targeted biopsy was driven by the highest grade group of the two. Methods Overall, 6588 patients received systematic biopsy plus MRI-targeted biopsy and radical prostatectomy. We assessed advanced stage (seminal vesicle or lymph node invasion with or without extraprostatic extension), adverse pathology (advanced stage or high grade group), and biochemical recurrence for each systematic biopsy and MRI-targeted biopsy grade group combination. Results Overall, 3405 (52%) had discordant grade groups. When systematic biopsy and MRI-targeted biopsy grades were discordant, the risk of advanced-stage disease was intermediate. For instance, the risk of advanced pathologic stage was 23% for grade group 3 on both systematic biopsy and targeted biopsy and 8.8% for concordant grade group 2. The risk was 18% for patients with systematic biopsy grade group 3 but targeted biopsy grade group 2 and 15% if the reverse were true. Similar results were seen for other outcomes. Conclusions When the grade group is discordant between systematic biopsy and targeted biopsy, the risk is intermediate. The current approach of assigning the highest grade group should be abandoned, and urologists should consider deescalating treatment intensity for patients with discordant systematic biopsy and MRI-targeted biopsy grade groups. Our findings are plausibly explained by pattern 4 volume being the primary driver of risk.