The Highest Grade Group Does Not Drive the Risk of Recurrence when Systematic and Multiparametric Magnetic Resonance Imaging (MRI)-targeted Biopsies are Discordant: Preliminary Findings Using Radical Prostatectomy Pathology as a Surrogate for MRI-targeted Biopsy Grade

Abstract

Pathology grading of prostate biopsy follows the rule that the highest International Society of Urological Pathology grade group (GG) is the GG assigned. This rule was developed in the systematic biopsy (SBx) era and makes sense when samples are from very different areas of the prostate. This rule has been kept for multiparametric magnetic resonance imaging (mpMRI)-targeted biopsy (MRI-TBx), for which multiple samples—targeted and systematic—are taken from small areas. In particular, if the results for SBx and MRI-TBx are discordant, the patient is assigned the higher GG. However, the most appropriate grading when MRI-TBx and SBx grades are discordant has never been investigated empirically. A cohort of patients who have undergone SBx and MRI-TBx with long oncological follow-up does not yet exist. To estimate the risk of recurrence for every combination of biopsy and pathological grades, we used the GG on radical prostatectomy (RP) as a surrogate for GG on MRI-TBx GG surrogate. We analyzed data for 12 468 men who underwent SBx and RP at a tertiary referral center and assessed 5-yr biochemical recurrence-free survival (bRFS) for each pairwise combination of biopsy and surgical GG results. We found that for cases with discordant SBx and RP grades, the risk of recurrence was intermediate, irrespective of whether the highest grade was at RP or SBx. For instance, the 5-yr bRFS rate was 57% for men with GG 3 on RP and 60% for men with GG 3 on SBx, but 63% for men with RP GG 3 and SBx GG 2, and 79% for men with RP GG 2 and SBx GG 3. Translating these findings to MRI-TBx casts doubt on current grading practice: when GGs are discordant between SBx and MRI-TBx, the risk of biochemical recurrence risk is not driven by the highest grade but by an intermediate between the two grades. Our findings should motivate studies assessing long-term outcomes for patients undergoing both MRI-TBx and SBx with a view to empirically evaluating current grading practices.

Patient summary

Patients with prostate cancer may undergo two biopsy types: (1) systematic biopsy, for which sampling follows a systematic template; and (2) targeted biopsy, for which samples are taken from lesions detected on scans. There may be a difference in prostate cancer grade identified by the two approaches. In such cases, the risk of cancer recurrence seems to be predicted by an intermediate grade between the lower and higher grades.