Conventional random biopsy had been the standard procedure for diagnosis of prostate cancer for decades, and it was not until recent years that MRGB was introduced into the paradigm of prostate biopsy with the advancement of mpMRI and fusion technique. Aside from the in-bore MRI targeted biopsy, which was less performed due to inconvenience, MRCB and MRFB are currently the two most performed methods for MRI-guided biopsies.
Reviewing previous literatures, few studies had performed comparison between the different methods of MRGB. The FUTURE trial had compared the 3 methods by multi-center randomized controlled trial7 and revealed that in-bore MRI biopsy had slightly higher PCa overall detection rate, while MRFB had higher csPCa detection rate. However, all the three biopsy methods showed no significantly difference among both PCa and csPCa detection rate. Another trial, the SmartTarget biopsy trial, which was a blinded, within-person randomized paired trial that compared the biopsy efficacy of MRCB and MRFB. The results from SmartTarget showed no difference between the two biopsy strategies and each of the biopsy method would miss 14% of total detected clinically significant cancers. Combining of the two biopsy methods could provide the highest diagnostic efficacy8. The PICTURE trial also compared the MRGB with transperineal template prostate mapping biopsies. The PICTURE trial concluded that MRGB can detect more csPCa with nearly tenfold less biopsy cores. Simmons et al also compared the MRCB and MRFB methods and found that although MRFB diagnosed slightly more csPCa than MRCB, there was no statistically difference9. Although similar diagnostic accuracy of MRCB and MRFB were reported in among the three trials, there were absence of any subgroup analysis investigating further possibilities.
In our study, we performed per-lesion analysis of MRCB and MRFB instead of within person comparison due to study design. In resemblance with the previous studies comparing the two methods, we also found no significant difference between MRCB and MRFB in PCa and csPCa diagnostic rate, biopsy Gleason score, and positive cores percentage in overall study population. Furthermore, in the subgroup analysis allocated by lesion size, we discovered that in the subgroup with lesion size less than 1.3 cm, MRFB diagnosed significantly more PCa than MRCB with significant higher positive biopsy rates for PCa and csPCa. The same difference was not observed in subgroup with larger lesion size and in overall population.
After searching through previous publications, we found no study discussing the impact of lesion size on the diagnostic accuracy of MRGB. Barrett et, al had compared the histological outcomes in patients undergoing MRFB and background systemic biopsy10 and found that the incremental benefit of MRFB was limited in patients with larger lesion size (short axis diameter > 1.0 cm). Although this study only examined the diagnostic value of MRGB in contrast with background SB and concluded that in larger sized lesions the efficacy of additional MRGB was limited, and implied that lesion size may also impact the diagnostic accuracy of MRGB, including MRCB and MRFB. The theorem was to some extent endorsed by our study which demonstrated MRCB would diagnose less lesions comparing to MRFB when target lesion size was less than 1.3cm and had lesser biopsy positive rates. Since MRCB is relied on both the visual cognition and mental correlation of the location, it is considered to be more operator dependent and would task individual surgeon’s experience. On the other hand, MRFB is a software-based fusion approach which, according to studies, may improve cancer detection and reduce the learning curve necessary for visual cognition. In sum, the benefit of MRFB is more prominent when targeting small lesions and/or conducting biopsy of a larger prostate, while MRCB can be adopted for those larger lesions as a comparable alternative11.
Another issue for prostate biopsy is the route for biopsy, including the trans-rectal approach (TR) and the trans-perineal approach (TP). Generally, TP approach are correlated with less complications, especially infectious events and are recommended by many clinical guidelines over TR approach recently. However, it is still debatable to date whether one approach is superior to the other with various clinical factors including: diagnostic accuracy in certain tumor location, deliverability in the outpatient clinic setting, and steepness of learning curve to be taken into consideration6. In a recent multicenter retrospective cohort study, Zattoni et, al suggested that TP approach could improve csPCa detection comparing to TR approach, especially in the transition zone, anterior zone, central zone, and apex6. In our study, we selected only patients with TP approach for analysis, thus we could exclude the potential bias from different biopsy routes.
Retrospective study design is the main limitation of this study, and this caused the selection bias of patients who received MRCB and MRFB with heterogenous baseline characteristics. The small sample size is also an important limitation and larger cohort is needed for validation of our findings. Furthermore, another limitation was from the paired study method, by which a portion of the patients would receive both MRGB and SB at the same time. Paired biopsies would be prone to bias as the surgeon had already identified the location of suspicion on MRI image and the selection of SB location may no longer be systemically randomized.