Limitations of MRI fusion biopsy include its cost, interobserver variability, and low diagnostic accuracy for clinically significant cancer in the anterior prostate.
Multiparametric MRI-ultrasound fusion biopsy (mpMRI fusion biopsy) has multiple limitations, including cost, interobserver variability, and low diagnostic accuracy for clinically significant cancer in the anterior prostate,1 says E. David Crawford, MD. Furthermore, according to the AUA Policy Statement on mpMRI in the diagnosis, staging, and management of prostate cancer, which provides a framework for clinical practice, mpMRI itself has a limited role as a diagnostic tool.2
Therefore, mpMRI fusion biopsy cannot be considered as the gold standard for prostate cancer diagnosis, according to Dr. Crawford, professor of surgery, urology, and radiation oncology, and head of the section of urologic oncology, University of Colorado Anschutz Medical Campus, Aurora.
“The coincidental timing of the advent of mpMRI technology with a higher field strength and the growing controversy about overdiagnosis and overtreatment of insignificant prostate cancer generated interest in using mpMRI to improve biopsy accuracy and efficiency. Then, as evidence began to accumulate showing that the MRI ‘fingerprint’ could be used to ferret out significant prostate cancer on transrectal biopsy, companies developed targeted biopsy platforms based on fusing the mpMRI image to the live transrectal ultrasound image for targeted biopsy,” Dr. Crawford said.
“Available evidence shows that these systems provide good accuracy for striking the lesions identified on mpMRI and, compared with systematic biopsy, increase the detection rate for higher grade cancers while decreasing detection of lower grade lesions. However, numerous studies also show that the accuracy of mpMRI fusion biopsy is not much better than cognitive fusion biopsy and that MRI fusion biopsy misses a significant number of high-grade cancers that are detected by 12-core systematic biopsy. Therefore, it cannot be relied on as the gold standard for prostate cancer diagnosis.”
“In fact, most centers offering MRI fusion biopsy combine it with 12-core systematic biopsy,” said Nelson Stone, MD, professor of urology and radiation oncology, Icahn School of Medicine at Mount Sinai, New York.
The performance limitation of mpMRI fusion biopsy is highlighted by the results of many studies that show it misses between 5% and 35% of high-grade cancers, including relatively large lesions.1,3
“The implications of missing this many high-grade cancers means that a negative mpMRI in a man with a suspicion of prostate cancer cannot be used to rule out a biopsy, men diagnosed with low-risk disease cannot be monitored with mpMRI alone, and this imaging technology cannot be used to plan focal therapy,” said Dr. Stone.
Dr. Crawford said, “Our research shows that 3-dimensional mapping biopsy is currently the most accurate biopsy method available.4 In addition, clinical data we have collected so far shows that 3-dimensional mapping biopsy diagnosed patients with high-grade (Gleason pattern 4 and 5) prostate cancer that was invisible on mpMRI.”
Dr. Crawford further contends that the fusion technique is not needed considering that areas of suspicion identified on mpMRI can be equally well targeted through cognitive co-registration, assuming the urologist has good ultrasound interpretation skills.
“I do both techniques, and when sampling areas with good accessibility, use of an mpMRI fusion system may have a slight accuracy advantage, but that remains to be proven,” Dr. Crawford said.
Dr. Crawford said that use of mpMRI fusion biopsy as an initial diagnostic test should be reserved for research studies conducted by experts.
“We need to consider that the best data for mpMRI fusion biopsy comes from studies done by expert radiologists and urologists at centers of excellence, and the findings do not necessarily translate to what is achievable in the hands of less experienced practitioners. To minimize the rate of missing high-grade cancers, it is important that the radiologist knows how to read and interpret the MRI,” said Dr. Crawford.
“We need a cost-effective, reliable technique that will guide the decision to perform biopsy because there is a high likelihood of finding high-risk disease, and that has been met through developments in genomic testing.”
To improve the accuracy and efficiency of prostate cancer diagnosis and risk stratification, Dr. Crawford and Neal Shore, MD, developed an algorithm based on the use of genomic markers.5 According to the algorithm, initial prostate biopsy is limited to men with PSA >1.5 ng/mL with at least one genomic test indicating the patient is at risk for high-grade prostate cancer.
“Patients may benefit from mpMRI when initial biopsies are negative and genomic tests identify a methylation abnormality signaling the risk for a significant prostate cancer. The mpMRI can help to identify these lesions and direct a biopsy,” Dr. Crawford said.
Disclosures: Drs. Crawford and Stone are owners of 3DBiopsy, Inc. Dr. Crawford is a consultant/speaker for MDxHealth, Genomic Health, Janssen, Dendreon, Ferring, and Bayer.
1. Filson CP, Natarajan S, Margolis DJ, et al. Prostate cancer detection with magnetic resonance-ultrasound fusion biopsy: The role of systematic and targeted biopsies. Cancer 2016; 122:884-92.
2. Fulgham PF, Rukstalis DB, Turkbey IB, et al. AUA Policy Statement on the Use of Multiparametric Magnetic Resonance Imaging in the Diagnosis, Staging and Management of Prostate Cancer. J Urol 2017;198(4):832-838.
3. Kim CK, Park BK, Kim B. Localization of prostate cancer using 3T MRI: comparison of T2-weighted and dynamic contrast-enhanced imaging. J Comput Assist Tomogr 2006; 30:7-11.
4. Crawford ED, Wilson SS, Torkko KC, et al. Clinical staging of prostate cancer: a computer-simulated study of transperineal prostate biopsy. BJU Int 2005; 96:999-1004.
5. PCMs™ Prostate Cancer Markers. Available at www.pcmarkers.com
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