Negative mpMRI does not rule out significant PCa

September 1, 2016

As interest in using multiparametric MRI as a diagnostic tool for prostate cancer increases, urologists should know that a negative mpMRI does not rule out significant prostate cancer, researchers advised at the AUA annual meeting in San Diego.

San Diego-As interest in using multiparametric MRI (mpMRI) as a diagnostic tool for prostate cancer increases, urologists should know that a negative mpMRI does not rule out significant prostate cancer, researchers advised at the AUA annual meeting in San Diego.

Related: Using mpMRI, 27% of men could avoid prostate biopsy

Jochen Walz, MD, and colleagues evaluated the accuracy of a negative mpMRI for ruling out significant prostate cancer in a retrospective study evaluating the histopathologic results after radical prostatectomy in 101 men. All of the patients had a normal preoperative mpMRI defined as PI-RADS v1 score <9 and no score >3 in any sequence, but underwent radical prostatectomy because of other unfavorable features relating to findings from PSA testing or findings on biopsy or digital rectal exam. 

Based on review of the histopathologic findings, only 24% of men were considered to have truly insignificant prostate cancer. pT3 disease was present in 17% of men, 12% had primary Gleason pattern 4 disease, almost 50% had secondary Gleason pattern 4 or 5 disease, and in 56% of men, the main tumor volume was ≥0.5 mL. Overall, 60% of the men were judged to have unfavorable pathology, defined as any Gleason pattern 4/5, pT3, or N1 disease.

“Some recent studies report that the negative predictive value of mpMRI is very high, above 90%, and it has been suggested based on these data that a negative mpMRI rules out significant prostate cancer. To the contrary, we found that a negative mpMRI is no warrantor for absence of significant disease,” said Dr. Walz, senior author of the study and head of urology, Institut Paoli-Calmettes Cancer Centre, Marseille, France.

“Because our study included a preselected population with other features suggestive of significant disease, we cannot make any statements about the negative predictive value of mpMRI in the general population. However, we do believe that whether mpMRI is being performed in the diagnostic or active surveillance setting, patients with a negative mpMRI should undergo further exploration.”

Because studies in the literature reporting high negative predictive values of mpMRI come from centers of excellence where there are highly experienced radiologists reading the images, Dr. Walz and colleagues explored differences in radiologist expertise as a possible explanation for the discrepancy between their findings and those from others. In their series, 29 of the images were read in-house by a dedicated uroradiologist, while the remaining 72 were done by radiologists in the community.

 

How expert, community radiologists compare

Overall, the expert’s interpretation seemed to be more reliable for excluding significant disease. Among the men whose images were read by the expert, only one (3%) had pT3 disease and only one (3%) had primary Gleason pattern 4 on histopathologic examination of the radical prostatectomy specimen. Among the men whose images were read by a radiologist in the community, 22% had tumor stage pT3 and 18% had a primary Gleason score of 4.

Also see: Is mpMRI ready for prostate Ca screening?

Nevertheless, 15 (52%) of the men whose mpMRI was read by the expert had secondary Gleason pattern 4, which represents a sizable number with significant disease, Dr. Walz said.

“Better training and quality assurance will improve the results of mpMRI and are of utmost importance before this technology is used as a screening or triage tool. However, no test is perfect, even in expert hands,” Dr. Walz told Urology Times.

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