Multiparametric-MRI in prostate cancer: An expert’s view

The use of multiparametric-magnetic resonance imaging (MRI) to help guide prostate biopsies has been growing among urologists and was the subject of an American Urological Association (AUA) and the Society of Abdominal Radiology Prostate Disease Focused Panel standard operating procedure document.1 In this interview, Marc A. Bjurlin, DO, MSc, FACOS, explains the advantages of prostate MRI, in which patients it is best used, and whether it can be considered the gold standard for prostate cancer detection. Bjurlin is an associate professor of urology at the University of North Carolina at Chapel Hill.

Can you describe the technology being used in prostate MRI?

MRI-guided biopsies can be performed in several ways. It’s most commonly performed in conjunction with a transrectal ultrasound, either with or without software assistance. When we use software assistance, this is the most common technique employed in the United States. In some situations, the software is not available, then we do MRI-guided biopsies based on what we refer to as “cognitive guidance” where, essentially, the urologist interprets the MRI and places needles freehand into the area of interest. There is also a technique in which men can be biopsied while in the MRI scanner itself; this is referred to as “in-bore” or “in-gantry” biopsy. As you can imagine, the more we move away from the transrectal approach, the more we can also perform MRI/ultrasound fusion biopsies by way of the transperineal approach.The transperineal approach avoids biopsying via the rectal wall, therefore significantly reducing the potential for bacterial infection. Furthermore, the transrectal approach to prostate biopsy may result in undersampling, particularly in the anterior prostate. The MRI/ultrasound-guided transperineal approach allows easy access to anterior prostate tumors.

What are the advantages of using prostate MRI?

Using MRI as a prebiopsy risk assessment tool, then using that technology to guide biopsy has several advantages. It’s been shown to increase the number of clinically significant cancers that are detected while simultaneously reducing the number of insignificant cancers detected. The biopsy of the region of interest reduces the number of biopsy cores taken per procedure, so ultimately, this may have a role in reducing adverse events and avoiding some biopsy-related complications. Using this approach of getting the MRI, identifying the region of interest, then biopsying that area has also been useful in terms of selecting men who may be candidates for focal therapy, as well as planning that focal therapy intervention.

For what types of patients is prostate MRI most ideal?

In 2018, we published the American Urological Association [AUA] policy statement on the use of multiparametric-MRI in the diagnosis, staging, and management of prostate cancer.1 We updated this statement in 2019. Essentially, the take-home message from this document is that when there is a quality prostate MRI, the current evidence supports MRI and MRI-targeted biopsy in men who are at risk for harboring prostate cancer who have not yet undergone a previous biopsy, as well as men who have an increasing prostate-specific antigen [PSA] followed by an initial negative biopsy. In men with low-risk disease who are on active surveillance, there is now more evidence that MRI is also useful in this space to help risk assess men to choose who would be an appropriate candidate for active surveillance and continue to be on active surveillance in light of an elevated PSA.

What are some of the drawbacks to utilizing prostate MRI?

Cost is a major issue, but some of the up-front costs are offset downstream, meaning that essentially by getting an MRI and doing an MRI-targeted biopsy, we have the potential to reduce the need for repeat biopsy in the future. We may reduce the number of insignificant cancers diagnosed, which may ultimately lead to a decrease in overtreatment of insignificant disease. We may also improve patient understanding and reduce anxiety when a patient has a better assessment of what their MRI looks like, and they understand the disease process.

There are some other limitations of MRI and MRI-targeted biopsy in that there is quite a bit of interobserver variability, meaning that different radiologists may interpret the MRI as having different risks. There have been several considerations in this area in terms of how to adjust interobserver variability. To reduce variability in prostate MRI interpretation, the American College of Radiology and the American Roentgen Ray Society offer a prostate MRI course with the goal of improving the interpretation of MRI of the prostate and establishing a quality assurance program for prostate imaging. Additionally, there will soon be an American College of Radiology Prostate Cancer MRI Center designation to help standardize MRI protocols and interpretation.

There are also some data that show several prostate cancers that are not visible on MRI; somewhere between 5% to 35% of MRIs may miss high-risk disease. Even though the MRI is a useful tool, it is not perfect by any means.

Overall, would you say that the benefits of MRI in prostate cancer justify the cost associated with it?

I think so, but with some caveats, one being that if we are going to get an MRI, we must make sure that the MRI is high quality. The big picture is that not every single man with an elevated PSA needs an MRI, and subsequently an MRI/ultrasound fusion biopsy. There are several risk stratification tools that can be employed in this shared decision-making process, including biomarkers and family history. I think a comprehensive approach really lends itself to further areas of research to determine when we should be using biomarkers, when we should be using MRI, and what the ideal combination of both is in order to help risk assess men, in terms of moving forward with a prostate biopsy.

How widespread is its use currently?

This technology has been leading the way in the United States and Europe, but it’s not widely adopted universally. I think that’s a result of many reasons. No. 1, at least in the United States, insurance coverage is still an issue. No. 2, there are up-front costs, in terms of purchasing the MRI/ultrasound fusion platform, as well as software and access to high-quality MRIs. Not all institutions have that.

At this point, would you say that MRI-guided biopsy is the gold standard for prostate cancer detection?

I think we’re heading in that direction, but again, with several caveats. In men who ultimately have had a shared decision-making experience and opted to undergo a biopsy, when a high-quality MRI can be obtained, an MRI/ultrasound fusion biopsy is the gold standard. With that being said, not every man with an elevated PSA needs this, and there are additional biomarkers and risk stratification tools that we should be incorporating into risk assessment to help guide men in terms of who needs a biopsy and who can avoid a biopsy.

Reference

1. Standard operating procedure for multiparametric magnetic resonance imaging in the diagnosis, staging and management of prostate cancer. American Urological Association. Updated May 2019. Accessed August 18, 2021. https://bit.ly/3yY04FH