Taken together, 136/162 lesions (84.0%) were correctly identified by MRI.
Eight lesions (4.9%) were prospectively identified, but tumor size was underestimated on MRI (Gleason score, 3+4; n = 5 [3.1%]; Gleason score, 4+4; n = 2 [1.2%]; Gleason score, 4+5; n = 1 [0.6%]).
A total of 26 (16%) lesions were missed during the initial interpretation (one per patient). Gleason scores in this patient subset were 3+4 (n = 17 [65%]), 4+3 (n = 1 [4%]), 4+4 (n = 7 [27%]), and 4+5 (n = 1 [4%]).
During the retrospective review, eight (31%) PI-RADS 1 lesions were not detected on MP MRI; 18 (69%) lesions were visible (PI-RADS 2, n = 7 [27%]; PI-RADS 3, n = 6 [23%]; PIRADS 4, n = 5 [20%]). Within this group, five (62%) were Gleason 3+4 lesions, and three (38%) were Gleason 4+4 lesions.
"We think that we can detect about half of the missed lesions and reduce the number of greatly underestimated lesions using computer-aided diagnosis algorithms," Dr Turkbey pointed out. "However, a number of patients will escape detection of their clinically significant prostate cancer using MRI alone. Therefore, we and many other centers continue to advocate for systematic biopsies in addition to targeted biopsies, and we are investigating several aspects of this phenomenon."
Only 16 Patients Underweent MP-MRI Before Biopsy: What That Means
Commenting on the study, Hashim U. Ahmed, PhD, BM, chair of urology and consultant urologic surgeon at Imperial College, London, United Kingdom, pointed out that all the patients in this series had biopsy-proven cancer.
"The patients had identifiable cancer already, and as the authors show, 99 of the 100 men had one clinically significant cancer lesion correctly identified by MRI," Dr Ahmed said. "So, for the individual, there is a large probability of MP MRI identifying a significant cancer."
He explained that it is already known that MP MRI has a miss rate for significant disease. In a clinical trial conducted earlier this year by Dr Ahmed and his colleagues, MP MRI administered as a triage test before the first transrectal ultrasound biopsy identified at least one quarter of all patients who could safety avoid undergoing a biopsy. Results of this study also suggested that this technology might improve the detection of clinically significant prostate cancer.
"If one uses template mapping biopsies, as we did in the multicenter, prospective, blinded, validation PROMIS study of 11 expert and nonexpert centers, no cancers of Gleason 4+3 or higher of any volume were missed by MP MRI," he said. "This is already leaps and bounds better than the current transrectal systematic biopsy."
This is already leaps and bounds better than the current transrectal systematic biopsy. Dr Hashim Ahmed
Dr Ahmed did note that the current study did have some methodologic problems.
"Only 16 of 100 were true prebiopsy MP MRI," he told Medscape Medical News. "We have known for over a decade that postbiopsy MRI scans are significantly degraded with biopsy-related inflammation and bleeding for between 3 and 6 months after a biopsy, and in some cases, up to 9 to 12 months. The study also only evaluated the two largest lesions on the report ? if there were significant MRI lesions after this upper limit of two, it seems the authors denoted them as 'negative' on the MP MRI."
In explaining another concerning factor, he said, "We also need to be cognizant of the fact that MP MRI will not be the sole source of cancer localization and extent. Did the biopsies detect significant disease just outside and adjacent to the MRI lesion and in other areas? We don't know this.
"We do know from a number of other studies, and this study confirms this, that MP MRI can underestimate the volume of the lesion on pathology," Dr Ahmed continued. "This information needs to be incorporated into targeted biopsy strategies and into treatment strategies, such as dose-escalation radiotherapy or focal ablative therapy."
The authors have disclosed no relevant financial relationships. Dr Ahmed has received funding from Sonacare Medical, Sophiris, and Trod Medical for clinical trials.
Radiology. Published online October 20, 2017. Abstract
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