#SUO14 - Session Highlights: Should MR be the standard of care before biopsy?

BETHESDA, MD USA (UroToday.com) - This discussion presented evidence for and against the use of MRI before biopsy. Given its potential for providing a non-invasive way to identify and localize possible prostate cancer foci, MRI use has expanded in recent years in the diagnosis of prostate cancer.

Dr. Samir Taneja presented the case for obtaining an MRI prior to biopsy. When lesions are seen on MRI prior to biopsy, they may be targeted either via cognitive localization or via an MRI-TRUS fusion biopsy platform. Dr. Taneja started by discussing the limitations of standard systematic biopsy, the most significant of which is sampling error. Strategies to overcome sampling error typically involve exposing patients to multiple repeat biopsies and increasing the number of cores obtained both of which increase costs and increase the likelihood of the discovery of clinically insignificant disease. Dr. Taneja outlined that biopsy optimization involves increasing the detection of clinically significant prostate cancer, decreasing over-detection of indolent disease, and improving localization while maintaining or improving cost-effectiveness. He argued that targeted biopsy via pre-biopsy multiparametic MRI (mpMRI) allows for improvement in prostate biopsies in all these categories.

suoDr. Taneja outlined the use of MR-targeted biopsy in 3 settings: in patients with no previous biopsy, in patients with previous negative biopsy, and in patients on active surveillance with clinically insignificant disease found on prior biopsy. He presented data from NYU which included a final cohort of 601 men who were enrolled in an MR-targeted biopsy study. He explained that at NYU, the rate of clinically significant cancer detection correlated with suspicion of cancer on MRI, while low-grade disease did not. He discussed that in patients with no prior biopsy, targeted biopsy alone detected more Gleason 7 or higher cancer and less Gleason 6 disease. He noted that some clinically significant disease, however, was missed, and so systematic biopsy in this setting is appropriate if maximal cancer detection is desired (with the caveat that it increases the possibility of the discovery of indolent disease). In the setting of patients with a prior negative biopsy, these patients have already undergone negative systematic sampling of the prostate, so repeat systematic targeted biopsy did not contribute much with regards to the detection of clinically significant cancer. In contrast, MR-targeted biopsy detected more Gleason 7 or higher cancers. Finally in the active surveillance setting, both MR-targeted and systematic biopsy resulted in significant rates of upgrading of disease, though the targeted biopsy performance was better. He did note that there was a small proportion of patients who were incorrectly risk-stratified by targeted biopsy alone.

He concluded by addressing criticisms of MRI use for prostate cancer diagnosis. He acknowledged that the efficacy of MRI in this setting is dependent on good study quality, as well as the experience of the person interpreting the study. He addressed the concern that MRI misses high-grade disease by presenting data from NYU of the 24 cases of clinically significant prostate cancer missed by MR-targeted biopsy. It demonstrated that the vast majority of these missed cancers were Gleason 3+4, with a low proportion of pattern 4, had low suspicion lesions on MRI, and were present for the most part in only a single core of the systematic biopsy. With regards to concerns for the cost of obtaining an MRI in every patient, Dr. Taneja showed data that demonstrated that, in the setting of patients with prior negative biopsies, the use of an MR-targeted biopsy actually resulted in an overall reduction of cost due to decreases in the diagnosis of indolent disease. He concluded that mpMRI allows for the improvement of biopsy performance in all settings, and may allow for the avoidance of biopsy and indolent cancer overdetection in patients with no or low suspicion lesions on MRI.

Dr. Andrew J. Stephenson presented the argument against the use of MRI prior to prostate biopsy. He discussed a review of the literature comparing MR-guided versus standard systematic biopsy and concluded that the outcomes he discovered were very mixed. While some studies demonstrate increased cancer detection rates with targeted biopsy, others show superiority of the systematic biopsy. He said that the assessment of the worth of MR-targeted biopsy depends on how many clinically significant cancers are missed by standard biopsy alone, whether or not MRI allows for the avoidance of standard biopsy, whether MRI localization and characterization of tumors provides clinically relevant information, and whether the use of MRI is cost-effective. He addressed each of these points individually. With regards to the effectiveness of systematic biopsy in detecting clinically significant disease, he presented data from the REDUCE trial where Gleason 8-9 tumors were seen in less than 1% of patients on systematic re-biopsy, and Gleason 4+3 tumors were seen in only 1.1%, indicating that standard biopsy does not miss many significant cancers. He discussed that the negative predictive value of mpMRI was low, ranging from 19-48%, and that targeted biopsy alone misses clinically significant cancers in up to 14% of patients arguing against MRI use precluding the need for a systematic biopsy. While targeted biopsy results in 23-47% of patients having their disease upgraded, these results are similar to a 20-33% reclassification rate among low-risk patients undergoing repeat standard biopsy.

Finally he addressed cost concerns. He pointed out that at the Cleveland Clinic, the use of an MR-targeted biopsy resulted in a 25% increase in the cost. He also noted that it resulted in a significant inconvenience for the patient via the need for an extra visit for the MRI which has unknown societal costs. He addressed the argument that MR-targeted biopsy might allow for a reduction in the cores obtained by stating that the literature does not support the notion that a decrease in core numbers results in decreases in the morbidity associated with prostate biopsy.

Dr. Stephenson concluded that mpMRI and MR targeted biopsy use and research is still in its infancy and has not matured to the point where the use of mpMRI prior to biopsy could be considered standard of care. He acknowledged that the potential exists for decreasing the need for unnecessary biopsy and decreasing the rate of detection of clinically insignificant cancers, however, he pointed out that, to date, there has been no proven benefit to the MRI-US fusion biopsy platform.

Of note, in an audience poll led by Dr. Laurence Klotz after the discussion, the vast majority of the audience agreed with Dr. Stephenson that at this time they would not obtain an MRI prior to biopsy. Only time will tell whether this opinion shifts in the future as the experience with mpMRI and MRI-targeted biopsy increases and further research emerges.

Presented by:
Samir S. Taneja, MDa and Andrew J. Stephenson, MDb
aNew York University School of Medicine; bCleveland Clinic Foundation

Moderated by:
Laurence H. Klotz, MD
Sunnybrook Health Sciences Centre 

Reported by:
Timothy Ito, MD
* from the 2014 Winter Meeting of the Society of Urologic Oncology (SUO) "Defining Excellence in Urologic Oncology" - December 3 - 5, 2014 - Bethesda, MD USA

*Fox Chase Cancer Center, Philadelphia, PA USA