Magnetic resonance imaging (MRI) as part of an approach to performing confirmatory biopsies among men on active surveillance (AS) for prostate cancer decreases the likelihood of AS failures and grade progression, according to updated findings from the prospective randomized ASIST trial.
For this trial, investigators randomly assigned 296 men eligible for AS to undergo a confirmatory biopsy with transurethral ultrasound (TRUS)-guided 12-core systematic sampling or MRI with systematic and targeting sampling. Initial findings showed no significant difference between the study arms in the proportion of men found to have Grade Group 2 or higher disease on confirmatory biopsy (23% in the systematic biopsy only arm vs 21% in the target biopsy group). For the follow-up study, a team led by Laurence Klotz, MD, of Sunnybrook Health Sciences Centre in Toronto, examined 24-month outcomes among 259 men who underwent confirmatory biopsies (132 in the non-MRI and 127 in the MRI arm). In this study, 101 men in the non-MRI arm (76%) and 98 in the MRI arm (77%) continued AS post-biopsy. AS failures occurred in 19% of the MRI group compared with 35% of the non-MRI group. Confirmatory biopsy detected clinically significant cancer in 9.9% of the MRI arm compared with 23% of the non-MRI arm. Both of these between-group differences were statistically significant.
“We think part of the explanation [for the different findings] is that there is a very important and significant learning curve for the process of MRI with fusion targeted biopsies,” Dr Klotz told Renal & Urology News. “At every step of a fairly complex algorithm, there can be errors in the quality of the MRI, the interpretation of the MRI, the registration of the suspicious area, and the fusion. Then, there is the targeting by the biopsy needle, and in every one of these steps there is room for error, and you need the whole thing to be done in a quality way to get an excellent outcome.”
He also observed, “We were more surprised by the initial findings that the MRI was not useful. It did not make sense. This performance of MRI was the worst performance from any large series that anyone had ever reported and we really couldn’t figure out why. We think the likeliest explanation for the change is that by chance there was an imbalance between the 2 arms in the number of patients who had high-grade cancer.”
Leonard G. Gomella, MD, Chair of Urology and Senior Director Clinical Affairs at the Sidney Kimmel Cancer Center of Thomas Jefferson University in Philadelphia, said much needs to be learned about the optimal approach to diagnosing PCa. “Not just simply finding the cancer but identifying those prostate cancers that are potentially life threatening,” Dr Gomella said. “MRI is becoming an important tool in that area, and this paper confirms it utility. However, the paper also points out that there still may be some important cancers that the MRI image cannot see. Additional biopsies of the prostate in areas that appear normal on MRI are warranted to provide the best information on the cancer that may be present in the prostate.”
Neil Desai, MD, Assistant Professor of Radiation Oncology at UT Southwestern Medical Center, Dallas, pointed out that PRECISION and PROMIS studies demonstrated the enhanced sensitivity of MRI-guided biopsy for variously defined clinically significant PCa compared with standard template TRUS-guided biopsy in initial diagnostic assessment of at-risk men. Although the study population in ASIST differed from that of the PRECISION and PROMIS studies, “I applaud the authors for a robustly conducted trial.”
He added, “As the authors note, the combination of a suspected chance imbalance in risk between the 2 randomized arms and potential learning curve related imperfections in the technique confound our ability to discern a causative benefit to the use of MRI-guided biopsy in this trial’s application.”
The available literature suggests that MRI-guided biopsy does increase sensitivity for detecting clinically significant PCa, he said, but remains unclear whether it is highly beneficial in the confirmatory biopsy setting of men already placed on AS.
Klotz L, Pond G, Loblaw A, et al. Randomized study of systematic biopsy versus magnetic resonance imaging and targeted and systematic biopsy in men on active surveillance (ASIST): 2-year post biopsy follow-up. Eur Urol. 2020;77:311-317.
Klotz L, Loblaw A, Sugar L, et al. Active surveillance magnetic resonance imaging study (ASIST): results of a randomized multicenter prospective trial. Eur Urol. 2019; 75: 300–309