SIU 2018: Can MRI Replace Prostate Biopsy?

Seoul, South-Korea (UroToday.com)  Dr. Ploussard debated the question whether mpMRI can replace prostate biopsies. The old prostate cancer diagnosis strategy used to be entail referring patients to a systematic prostate biopsy based on PSA, PSA density, digital rectal examination (DRE) and previous biopsy history. However, the new paradigm is the imaging based strategy, whereby in the first step, aside from obtaining all relevant clinical history, DRE and PSA, the patient is also sent to a prostate mpMRI. In the next step, the patient undergoes a targeted biopsy or a combination of both targeted and systematic biopsies, if the mpMRI is positive.

However, this new imaging based strategy is not perfect, as mpMRI does not detect all significant prostate cancers. The true false negative rate is still unknown. The negative predictive value of mpMRI ranges from 63% to 91% for prostate cancer detection. The risk of missing clinically significant prostate cancer in case of a negative mpMRI is between 10-40%. Additionally, the rate of missing prostate cancer depends on the mpMRI suspicion score, the radiologist’s experience in reading mpMRI, the Gleason grade and tumor size, and the cancer prevalence. Fortunately, in the vast majority of cases, the cancers missed by mpMRI and targeted biopsies are low grade cancers. 

There are two pivotal trials that imaging based strategy is based on. These are the PROMIS 1 and the PRECISION 2 trials. In the PROMIS trial, mpMRI was assessed to see whether it was superior to systematic biopsy in order to rule out significant prostate cancer. In the PRECISION trial, the sequence of mpMRI followed by targeted biopsy (if the mpMRI was positive) was examined to see if it was superior to systematic biopsy alone to detect clinically significant cancer.

In the PROMIS trial the negative predictive value of mpMRI was shown to be higher than that of transrectal ultrasound (TRUS) guided biopsies, with 25% of biopsies avoided and more than 90% of clinically significant cancers being detected. In the PRECISION trial, 25 centers from 11 countries were involved. The primary endpoint was detection of significant prostate cancer. Systematic biopsy alone was compared to mpMRI with or without targeted biopsy. The results showed that the mpMRI arm fared better, with 28% of patients managing to avoid biopsies and having less low grade complications. More significant prostate cancer (38% vs. 26%) and less insignificant prostate cancer (by 13%) was diagnosed by the mpMRI arm. Unfortunately, mpMRI does miss 30% of high grade cancer foci. 3 There is no doubt that mpMRI performance is very much dependent on the experience of the radiologist reading it.

In a study focusing on the follow-up of patients who had a negative mpMRI, within 5 years, their risk of developing clinically significant  prostate cancer was 5%, while any prostate cancer, was 16%. 4 Therefore, the authors concluded that negative mpMRI entails a low risk of subsequent detection of clinically significant prostate cancer, and that a negative mpMRI is at least equal to a negative mpMRI and systematic biopsy. Using systematic biopsy only, approximately 10-20% of clinically significant prostate cancer would be missed. In mpMRI targeted biopsy 10% of significant cancers would be missed, while using the combination of both targeted and systematic biopsies would be the most ideal with lowest percentage of clinically significant prostate cancers missed.

Dr. Ploussard summarized his great talk with some take home messages. The benefit of mpMRI and targeted biopsies in clinical practice is clear and should not be debated. mpMRI must be included in the prostate cancer risk assessment, and be a part of the biopsy decision making. It is important that  we remember, that despite its advantages, mpMRI might miss 10% at least of clinically significant prostate cancer. Additionally, Dr. Ploussard recommends using mpMRI even before the first biopsy. Lastly, systematic biopsy might still have a role in high risk prostate cancer patients, even if the mpMRI is negative. But, we need to avoid systematic biopsies in patients who are at low risk with a negative well-read and interpreted mpMRI.

Presented by:Guillaume Ploussard, MD, Toulouse, France

References: 
  1. Ahmed HU et al. The Lancet 2017
  2. Kasivis et al. NEJM 2018
  3. Le et al. Eur Urol 2015
  4. Panebianco et al. Eur Urol 2018
Written By: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre  Twitter: @GoldbergHanan at the 38th Congress of the Society of International Urology - October 4- 7, 2018 - Seoul, South Korea
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