Magnetic resonance imaging (MRI) can aid in identifying prostate tumors undetectable by digital rectal examination (DRE) and in biopsy specimens, researchers concluded.

The investigators called these prostatic evasive anterior tumors (PEATS). They advise clinicians to consider the possibility that PEATS may be present in patients with a negative biopsy or DRE but a high PSA level or PSA velocity.

“These are not necessarily something you would find any other way besides MRI,” lead investigator Masoom Haider, MD, Associate Professor of Radiology at the University of Toronto, told Renal & Urology News. Dr. Haider estimates that approximately 5%-15% of patients with a PSA level greater than 10ng/ml and at least two prior negative biopsies may have PEATS.

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Dr. Haider and the other team members came upon the phenomenon of PEATS when they retrospectively reviewed the MRI database from the University Health Network in Toronto and identified 31 patients who had anterior predominant tumors on MRI.

Fourteen of these men were on active surveillance for low-volume disease when they were referred for an MRI. They had a median PSA level of 10 ng/mL, an average prostate volume of 28.5 mL, and a PSA density of 0.44. The other 17 patients had an average of two previous negative biopsies and a median PSA of 12 ng/mL, prostate volume of 35 mL, and PSA density of 0.36.

Eighty-five prostate-biopsy cores from the anterior prostate were available for retrospective review. Forty-four (52%) contained cancer. There also were 314 cores available that were from the peripheral zone, and 39 (12%) of these were positive.

Thirteen of the 31 men had a radical prostatectomy. Three of these men had pT2 disease, seven had pT3 and the remaining three had stage pT4. In addition, seven of the 13 (54%) men had positive surgical margins compared with a 26% rate of positive surgical margins among all men with stage pT3-4 disease in the same period.

The investigators concluded that MRI can help to direct biopsies to the anterior prostate with a high degree of accuracy, and that PEATS is more aggressive than might be expected, according to a report in BJU International (2009; published online ahead of print). They do not advocate the use of MRI in all cases.

“However, we believe that once adequate anterior and TZ [transition zone] biopsies have been taken … a subgroup of patients might benefit from using MRI to locate the tumors,” they wrote.

Specifically, candidates for MRI include patients who have a negative biopsy or low volume, low Gleason grade disease, and discrepantly elevated PSA or PSA dynamics. Further work is necessary to define optimal MRI utilization, he said.