SIU 2017: MRI As a Triage Test in Prostate Cancer Diagnostic Algorithm in Biopsy

Lisbon, Portugal (UroToday.com) With the use of mpMRI increasing, there is growing enthusiasm to utilize it in other spaces within the management of prostate cancer. At this time, it is currently approved and recommended for patients with prior negative TRUS systematic biopsy for an elevated PSA, patients on AS prior to repeat biopsy, or in local staging purposes prior to definitive therapy. However, it has not yet been proven to be effective as part of the diagnostic workup prior to initial biopsy. Part of the concern of doing an upfront MRI is that it is an expensive test in some countries or its accessibility isn’t easy, making it a harder decision to do this prior to a systematic biopsy – which, while invasive, is much easier to accommodate.

However, certain health care systems are evaluating it in this earlier role already. For example, certain institutions in the UK through the NHS are obtaining initial mpMRI prior to initial biopsy. Some private practitioners in the United States are doing this as well. But, as of yet, there is no strong evidence for this.

In this study, the authors review their experience with mpMRI prior to combined fusion/systematic TRUS biopsy in a population of 132 biopsy naïve men (age <= 75, mean age 62, normal DRE, median PSA 7.15 ng/mL). The mpMRI was completed on a 1.5T MRI machine using a surface and endorectal coil (no comment on phases utilized).

Clinically significant prostate cancer was defined as Gleason score >= 7 OR >50% of prostate cancer in a single core (though core length was not commented on). Overall detection of prostate cancer and detection of clinically significant prostate cancer was assessed, stratified based on MRI findings: MRI negative (PIRADS < 3), MRI with PIRADS 3, 4 or 5. They lastly calculated the number of avoided biopsies.

Based on this, they identified 29, 27, 55 and 15 men with negative MRI, PIRADS 3, 4 and 5 lesions, respectively. In terms of detection, as expected, PIRADS 4 and 5 identified the majority of cancer, and of clinically significant prostate cancer (50/65 cancers, 43/49 clinically significant prostate cancers). If the cutoff of <3 was used as a negative test, then they stated 21.9% of all biopsies could be avoided, but 2% of clinically significant prostate cancer would be missed. Those numbers jump to 56.3% and 8.2%, respectively, if PIRADS 3 lesions are also consider negative.

There are very major flaws with this study:

1) The authors fail to assess or comment on whether the systematic biopsy cores alone would have picked up those same cancers, independent of the targeted cores. Its quite possible that the clinically significant cancers were all picked up by the systematic biopsy.
2) Many patients don’t have just one or two PIRADS lesion – how were these patients classified? By the highest PIRADS score?

It is important to address these concerns. A recent trial by Dr. Lawrence Klotz (Toronto) found that MRI targeted biopsies missed a significant number of clinically significant prostate cancers that were picked up on systematic biopsy alone. Based on those results, it appears to be too early to say that mpMRI can be used to forego initial biopsy.

Presented by: Jiří Stejskal
Affiliation: Thomayer Hospital, Prague, Czech Republic

Written by: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre.Twitter: @GoldbergHanan at the 37th Congress of Société Internationale d’Urologie - October 19-22, 2017- Lisbon, Portugal

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