MRI-targeted biopsies pick up as many higher-grade tumors as do systematic biopsies during active surveillance (AS) for prostate cancer, according to results from the ASIST trial.

"The main value of MRI in men on AS is early identification of large, high-grade cancers missed on the diagnostic biopsy," said Dr. Laurence Klotz from Sunnybrook Health Sciences Center, in Toronto, Canada. "It does not preclude systematic biopsies, nor should it be used on its own as a trigger for intervention."

Dr. Klotz and colleagues evaluated the effectiveness of MRI-targeted biopsies versus conventional systematic biopsies in identifying higher-grade prostate cancer in their randomized trial of 273 men diagnosed with low-risk prostate cancer within the past year.

MRI-targeted biopsies

MRI identified regions of interest for biopsy in 64% of men, with 26% of targets considered anterior (a location that is less reliably evaluated by transrectal ultrasound), the team reports in European Urology, online July 13.

The primary outcome, the proportion of men whose confirmatory biopsy was upgraded to grading group 2 or higher, did not differ significantly between the MRI arm (21%) and the systematic-biopsy arm (23%); results were similar after central pathology review (33% versus 27%, respectively).

MRI is a useful adjunct, but

1. Negative MRI does not preclude a systematic biopsy,

2. Systematic biopsies still need to be done in men having a targeted biopsy, and

3. In men with low-grade prostate cancer, the presence of a region of interest should not on its own be an indication for treatment (i.e., one can't assume it is high-grade cancer).

Dr. Sanoj Punnen from Sylvester Comprehensive Cancer Center at the University of Miami, Florida, who recently reviewed the role of MRI for selection and monitoring of men on AS.

"The thought is that MRI can help localize cancer within the prostate, and there is lots of data that show using MRI, and targeted biopsy finds more high-grade cancer than typical random biopsy," said Punnen. This is mainly in the diagnostic setting, but even in active surveillance we have seen studies showing the benefit of MRI."

"However, in this RCT we failed to see a difference in the detection of aggressive cancer between an MRI-based approach and standard of random care biopsy," he said.

"This was a surprise to me. However, when you look at the cohort, we have to realize it is restricted primarily to low risk and therefore these patients were very selected. Also, while about 60% of patients had an MRI-visible lesion, about 20% of these were indeterminate lesions, which often have a low hit rate."

"However, the criteria for observation is expanding, and we are doing surveillance in more intermediate-risk patients, where MRI may have its most benefit," said Dr. Punnen, who was not involved in the trial.

"Furthermore, further studies like this with broader inclusion criteria need to be done to validate these findings and help identify which group of patients benefits the most from MRI," said Dr. Punnen.