Using mpMRI, 27% of men could avoid prostate biopsy

Chicago-Multiparametric magnetic resonance imaging (mpMRI) identifies a significant percentage of men who present with an elevated serum PSA level who may safely avoid prostate biopsy, British researchers report.

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Dr. AhmedStudy findings, including a sensitivity of >90% for clinically significant cancer and a negative predictive value (NPV) of 89%, “justify [mpMRI’s] use as a triage test to identify those men who might avoid a primary biopsy,” said first author Hashim U. Ahmed, BM, BCh, PhD, speaking at the American Society of Clinical Oncology annual meeting in Chicago.

In a study known as PROMIS, with use of mpMRI prior to transrectal ultrasound biopsy (TRUS), and a sampling strategy based on the MRI findings, “27% of men could avoid a biopsy altogether, we believe safely,” he said. “mpMRI followed by biopsy can reduce the over-diagnosis of clinically insignificant prostate cancers and identify over 90% of men with clinically significant prostate cancers.”

Men with an elevated PSA or other risk factors are currently undergoing transrectal ultrasound-guided biopsies, which have a number of errors, such as the diagnosis of clinically indolent cancers, lack of detection of clinically significant lesions, and misclassification of important cancers as unimportant, said Dr. Ahmed, clinician scientist and honorary consultant urologic surgeon, University College London Hospitals, London.

Within that context, PROMIS was designed to assess the ability of a 1.5 Tesla mpMRI prior to first biopsy to identify men who can safely avoid unnecessary biopsy, reduce over-diagnosis of clinically insignificant cancer, and improve the detection of clinically significant cancer.

Next: How the study was conducted

The trial used a paired cohort validating design in which all men at risk who were identified with an elevated serum PSA level up to 15 ng/mL or an abnormal digital rectal examination were asked to participate. Men underwent an mpMRI in 11 centers across the United Kingdom and had a 1.5 Tesla scan with no endorectal coil, followed by a prostate biopsy under general anesthesia. They underwent standard TRUS, as well as a template transperineal mapping biopsy at 5-mm sampling frame.

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A Likert 1 to 5 scale was used for reporting the results of mpMRI, with 1 representing the probability of an insignificant cancer being highly unlikely and 5 representing a probability of significant cancer being highly likely. Three was considered equivocal, so a score of 3 or greater was used as a positive scan for determining accuracy of MRI.

Clinically significant cancer was defined as primary pattern 4 or greater or a high burden of low-grade disease. Patients and the physicians were blinded to the mpMRI, and pathologists were blinded to the outcome.

“If we were to use MRI as a triage test to identify men who could avoid a biopsy, then we need a high sensitivity and a high NPV,” said Dr. Ahmed. In the 576 men who underwent all three blinded tests, sensitivity for clinically significant cancer was far superior with mpMRI compared with TRUS biopsy (93% vs. 48%; p<.0001) as was negative predictive value (89% vs. 74%; p<.0001).

TRUS biopsy had a specificity of 96% and a positive predictive value (PPV) of 90%. mpMRI had a specificity of 41% and a PPV of 51%.

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“There was a strong correlation between the MRI score and the presence or absence of clinically significant disease, with score 4 and 5 highly likely to be harboring significant cancer,” he said.

TRUS biopsy missed 119 clinically significant cancers whereas mpMRI missed only 17.

Next: mpMRI misses fewer high-volume cancers

mpMRI misses fewer high-volume cancers

Compared with TRUS biopsy, mpMRI missed fewer high-volume Gleason 6 cancers (one vs. seven) and fewer high-volume Gleason 3+4 cancers (16 vs. 99). mpMRI missed no primary Gleason 7 or greater cancers compared with 13 for TRUS biopsy.

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“The high sensitivity and NPV of prostate mpMRI at 1.5 Tesla without an endorectal coil within a multicenter setting justify its use as a triage test to identify those men who might avoid a primary biopsy,” said Dr. Ahmed. “However, the low specificity and PPV of prostate mpMRI indicate that men should still undergo a biopsy if they have a suspicious MRI.”

Twenty-seven percent of the men in this series could safely avoid a biopsy by using a sampling strategy based on the mpMRI findings compared with a strategy in which every man had a TRUS biopsy, he said, and there would be 5% fewer diagnoses of insignificant cancer.

Dr. Ahmed has received honoraria from AZTherapies, Janssen Oncology, and SonaCare Medical, is on the speakers’ bureau for SonaCare Medical, and has received travel, accomodations, and expenses from AZTherapies and SonaCare Medical. His institution has received research funding from AngioDynamics, Hitachi Chemical, SonaCare Medical, Sophiris Bio Inc., and Trod Medical. Several of his co-authors have a financial or other relationship with pharmaceutical companies.

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