Improved biopsy efficiency with MR/ultrasound fusion-guided prostate biopsy

With the current controversy regarding the overdiagnosis and overtreatment of screen-detected prostate cancer (PCa) ( 1 ), the urologic community has focused efforts on identifying tools to improve patient risk stratification. Magnetic resonance imaging (MRI) and MRI-targeted biopsy (MRITB) have emerged as promising solutions ( 2 ). MRI offers a reduction in overdiagnosis by providing improved prebiopsy risk stratification and decreasing the detection of low-risk PCa. Additionally, MRITB may reduce overtreatment by providing a more accurate assessment of cancer location, grade, and size. In the current study ( 3 ), the authors utilize outcomes from their previously published MRITB cohort ( 4 ) to better define the benefits of MRITB. They examine the biopsy efficiency of MRITB compared with standard 12-core transrectal ultrasound (TRUS)–guided biopsy, with each patient serving as his own control. This series of 1003 men includes both biopsy-naive (196/1003 = 20%) and previous negative biopsy (432/1003 = 43%) cohorts. The entire cohort was at relatively high clinical risk for PCa as evidenced by mean PSA 10.0 ng/mL and 83% of patients with PIRADS 4 or 5 suspicious MRI lesions. Additionally, a large proportion of patients had anterior lesions (44% of patients), which favors the diagnostic yield of MRITB over standard template TRUS biopsy ( 5 ). The advantage of MRITB is demonstrated by the significantly higher PCa yield on a per-core basis for MRITB, with 28% of targeted cores positive for PCa vs 14% of standard cores. MRITB provided a higher yield over standard biopsy for both the biopsy-naive and previous negative biopsy cohorts: 32% over 19% for biopsy-naive patients and 21% over 7% of cores for previous negative biopsy patients. The authors also demonstrated that MRI is a strong tool for risk stratification as biopsy yield improved with increasing MRI suspicion; 55% of cores from PIRADS 5 and 27% of cores from PIRADS 4 suspicious regions were positive for PCa while 14% of standard cores were found to be positive for PCa. Further demonstrating that MRI is a risk stratification tool, the authors note that when MRITB cores were negative the detection rate for higher risk PCa (Gleason 4 + 3 = 7 or greater) elsewhere on the gland on standard biopsy was very low (4%). These data on biopsy efficiency define the technical superiority of MRITB over standard TRUS biopsy, but how does this translate to improved patient outcomes? Although the study was not designed to demonstrate the reduction in patient morbidity or healthcare cost using MRITB, it is empirical that decreasing the overdiagnosis of clinically insignificant PCa would have a great impact on both of these endpoints ( 6–8 ). The authors examine the number needed to biopsy for patients with low-suspicion MRI and find that for every 13 patients who undergo MRITB rather than standard biopsy one fewer case of low-risk PCa will be diagnosed. Additionally, MRITB would likely be associated with less patient morbidity as an intuitive outcome of taking fewer biopsy cores in fewer patients per diagnosis of PCa ( 9 ). The conclusions of this study add to the increasing evidence that MRI and MRITB serve as an effective risk stratification tool for PCa diagnosis. Many additional important questions must be answered before we should widely adopt MRI as an adjunct for PCa diagnosis. For biopsy-naive and previous negative biopsy patients, we must identify what constitutes sufficiently low clinical risk for aggressive disease (based on PSA, age, race, digital rectal examination, family history, and other laboratory and genetic markers) as to avoid biopsy if MRI is negative or is low suspicion ( 10 , 11 ). For patients considering active surveillance, we must identify if an MRI-based strategy, such as the use of MRITB as a confirmatory biopsy and only pursuing repeat biopsy for changes in MRI appearance, limits patient morbidity while also minimizing any missed aggressive PCa ( 12 ). Finally, in the current health care environment, we must examine if the MRI-based diagnostic paradigm increases or decreases total health care costs per diagnosis of PCa and, if so, decide if the extent of reduction in overdiagnosis and overtreatment is worth this additional cost (13).