Randomized Study of Systematic Biopsy Versus Magnetic Resonance Imaging and Targeted and Systematic Biopsy in Men on Active Surveillance (ASIST): 2-year Postbiopsy Follow-up.

Background: The initial report from the ASIST trial showed little benefit from targeted biopsy for men on active surveillance (AS) for prostate cancer. Data after 2-yr follow-up are now available for analysis.

Objective: To determine if there was a difference in the AS failure rate in a 2-yr follow-up period among men undergoing magnetic resonance imaging (MRI) before initial confirmatory biopsy (CBx) compared to those who did not.

Design, Setting, And Participants: This is the 2-yr post-CBx follow-up for the ASIST trial, a prospective, randomized, multicenter, open-label study for men with Gleason grade group (GG) 1 cancer eligible for AS. Patients were randomized to CBx with 12-core systematic sampling or MRI with systematic and targeted sampling.

Outcome Measurements And Statistical Analysis: Patients with GG ≤ 1 on CBx were followed for 2 yr and had MRI and biopsy at that time point. Patients failed AS if they were no longer under AS because of grade progression, clinical progression, subject choice, clinical judgment, treatment, or lost to follow-up. Clinically significant cancer (CSC) was defined as GG ≥ 2.

Results And Limitations: In total, 259 men underwent CBx, 132 in the non-MRI and 127 in the MRI arm. After biopsy, 101 men in the non-MRI arm (76%) and 98 in the MRI arm (77%) continued AS. There were fewer men with AS failures in the MRI (19/98, 19%) compared to the non-MRI group (35/101, 35%; p =  0.017). At 2-yr biopsy there were fewer men with CSC in the MRI arm (9.9%, 8/81) than in the non-MRI arm (23%, 17/75; p =  0.048). Significant differences in AS failure rates were detected across the three centers in the MRI arm only (4.2% [2/48] vs 17% [4/24] vs 27% [7/26]; p =  0.019).

Conclusions: Baseline MRI before CBx during AS results in 50% fewer AS failures and less grade progression over 2 yr. The center where MRI and targeted biopsy is performed may influence AS failure rates.

Patient Summary: The ASIST trial randomized 273 men on active surveillance with low-grade prostate cancer diagnosed within the last year to systematic biopsy or magnetic resonance imaging (MRI) with systematic and targeted biopsy. The initial report showed little benefit from targeted biopsy. However, after 2 yr of follow-up we found that baseline MRI before confirmatory biopsy resulted in 50% fewer failures of surveillance and less progression to higher-grade cancer. This confirms the value of MRI in men on surveillance. This study is registered at ClinicalTrials.gov (NCT01354171).