Multiparametric magnetic resonance imaging (MP-MRI) can clarify which men with an elevated PSA (up to 15 ng/mL within 3 months) can safely avoid an immediate prostate biopsy and improve the accuracy of prostate cancer (PCa) diagnosis, according to a new study.

In the blinded PROMIS trial (NCT01292291), Hashim U. Ahmed, FRCS, PhD, BM, BCh (Oxon), of the University College London Medical School in the United Kingdom (UK), and colleagues  compared findings from 1.5 Tesla MP-MRI biopsy with transrectal ultrasound-guided (TRUS) biopsy against transperineal template prostate mapping (TPM) biopsy as a reference. The investigators posited that TPM is more accurate than TRUS-biopsy as a reference because it samples the entire prostate every 5 mm with an estimated 95% sensitivity for clinically significant PCa, and it is less prone to selection bias than radical prostatectomy specimens. Clinically significant cancers were defined as Gleason score 4 + 3 or above or a maximum cancer core length of 6 mm or longer.

Of 576 biopsy-naïve men from 11 centers in the UK, 71% had cancer based on standard TRUS biopsy (10 to 12 cores) with 40% of cases deemed clinically significant. MP-MRI proved more sensitive at finding significant cancers than TRUS biopsy (93% vs 48%), but was less specific (41% vs 96%). MP-MRI elucidates prostate volume, cellularity, and vascularity.

“The lower specificity and positive predictive value of MP-MRI means that a biopsy is still required with a suspicious MP-MRI,” Dr Ahmen and colleagues explained in a paper published online in the Lancet. “Men with suspicious MP-MRI areas can have biopsies guided by these findings. Overall, this strategy could improve detection of clinically important prostate cancer and reduce the number of men diagnosed with clinically unimportant disease.”

Imaging men first with MP-MRI might avoid biopsy in 27% of men and prevent 5% of overdiagnoses, the investigators estimated. In addition, when TRUS biopsies are guided by MP-MRI findings, up to 18% more clinically significant cancers might be detected than with TRUS biopsy alone.

Among the study's limitations, men with prostates greater than 10 mL were excluded from the trial to accommodate the use of TPM. In addition, TRUS biopsy was performed after TPM biopsy, so it is possible that swelling, distortion, and tissue disruption may have occurred and affected results. This study did not target MR-suspicious lesions so it cannot comment on the utility of targeted biopsy. A cost analysis of using MP-MRI in this context is forthcoming.

With regard to adverse effects, 5.9% of all recruited patients reported serious adverse events, including 8 cases of sepsis following urinary tract infection.

Standard 12-core prostate biopsies should continue to be performed in men despite the absence of suspicious prostate lesions on magnetic resonance imaging (MRI) scans, investigators reported at the Society of Urologic Oncology 17th annual meeting in San Antonio, Texas. In a study, they found that prostate MRI missed 13% of high-grade prostate tumors that were revealed by subsequent standard template transrectal ultrasound (TRUS) 12-core biopsy.
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“There is no doubt that MRI targeted biopsy is better than a random TRUS biopsy, but it is imperfect,” lead investigator Eric Kim, MD, told Renal & Urology News. “Currently, optimal cancer detection requires both targeted and systematic biopsy. As MRI interpretation and other imaging modalities, such as PET [positron emission tomography], improve, systematic biopsy may not be needed.”

Dr Kim and his colleagues at Washington University School of Medicine in St. Louis defined the negative predictive value (NPV) of prostate MRI at their institution and the characteristics of men with clinically significant cancer (Gleason 7 or higher PCa) but a negative MRI. 

They studied 84 men with negative prostate MRI who subsequently underwent standard template transrectal ultrasound-guided prostate biopsy. The group consisted of 39 biopsy-naïve patients, 30 patients who had a previous negative biopsy, and 15 patients on active surveillance (AS). All of the AS patients had been diagnosed with Gleason 6 cancer. The researchers calculated the NPV of prostate MRI as the number of TRUS biopsies divided by the sum of negative and positive TRUS biopsies.

Results showed that MRI had an NPV of 87% for Gleason 7 or higher PCa, which the investigators said is in line previously published studies. The only predictor of Gleason 7 or higher cancer among negative MRI patients was an increasing Prostate Cancer Prevention Trial risk calculator estimate for high-grade PCa. Dr Kim's group reported finding no significant differences in NPV between patients based on prior biopsy status.