Missing the mark? Prostate cancer upgrading by systematic biopsy over fusion biopsy.

Abstract

62 Background: Multiparametric MRI (mpMRI) and fusion biopsy (FBx) detect more high risk prostate cancer (CaP) and less low risk CaP than standard systematic biopsy (SBx). However, there remains a small subset of patients where SBx captures higher grade disease than FBx. We aim to identify potential reasons for failure of FBx biopsy in detection of clinically significant (CS) CaP. Methods: A review was performed of a prospectively maintained database of patients undergoing mpMRI followed by FBx and SBx in the same session from 2007−2014. Patients upgraded to higher risk disease based on SBx results relative to FBx were identified. Independent re−review of MR imaging in this subset was conducted to identify potential proximity between MR targets and SBx region which revealed higher risk CaP. Univariate analysis was performed to determine association of patient, MRI, and pathologic characteristics with upgrading by SBx. Results: We identified 1003 total patients who underwent mpMRI and biopsy, of which 564 were found to have CaP (56.2%). Upgrading based on SBx occurred in 137/564 (24.3%) patients, of which only 55 (9.8%) were to intermediate (high volume 3+4) [N = 37, 6.5%] or high risk CaP ( ≥ 4+3) [N = 18, 3.2%]. 41 of 55 patients (75%) had a lesion identified by mpMRI with FBx in the same sextant in which SBx biopsy revealed intermediate or high risk CaP. On univariate analysis, higher prostate volume (48cc vs 42cc, p < 0.001) and lower percent core involvement (20% vs. 58%, p < 0.001) were associated with upgrading by SBx. Conclusions: MRI rarely misses CS CaP and FBx, if accurate, should reflect the true disease state. Most gleason upgrades by SBx were to low risk, low volume CaP. In patients upgraded by SBx to CS CaP, mpMRI identified a targetable lesion in proximity to the SBx sextant in a majority of patients. FBx failure may be related to suboptimal imaging or biopsy related inaccuracy including registration error, miscalculation of target location, or inadequate lesion sampling. Other possibilities include presence of tumor heterogeneity, multi−focality within the same sextant, or low volume disease. Future studies with biopsy mapping on MRI will provide insight into mechanisms of failure in patients with overlapping target and sextant sampling.