Active Surveillance Magnetic Resonance Imaging Study (ASIST): Results of a Randomized Multicenter Prospective Trial

This study aimed to determine, in men recently diagnosed with grade group 1 (GG1) prostate cancer, if magnetic resonance imaging (MRI) with targeted biopsy could identify a greater proportion of men with GG ≥2 cancer on their confirmatory biopsy compared with systematic biopsies. The study was registered with www.clinicaltrials.gov (NCT01354171).

This study is a prospective, randomized, multicenter, open-label trial. Eligible patients were men diagnosed with GG1 cancer within 1 yr prior to study entry in whom a confirmatory biopsy was indicated. Patients were randomized to 12-core systematic biopsy or MRI with systematic and targeted biopsy using the Artemis fusion targeting system. The primary end point was the proportion upgraded to GG ≥2 in each arm.

In total, 296 men were registered and 273 randomized. Of the MRI group, 64% had a region of interest. No difference was observed in the rate of GG ≥2 upgrading (the intent-to-treat population, p=0.7, and per-protocol [PP] population, p=0.4), GG ≥2 upgrading within each stratum separately, or GG ≥3. After central pathology review, upgrading was observed in 36/132 (27%) men in the systematic biopsy arm and 42/127 (33%) men in the MRI arm (p=0.3). Upgrading was seen in 19/137 (14%) patients in the MRI arm on targeted biopsy alone (median, 2 cores) compared with 31/136 (23%) in the systematic biopsy arm (median, 12 cores; p=0.09). In the MRI arm, 8/127 (6.5%) patients had GG ≥2 disease identified on targeted biopsy, but ≤GG1 on the systematic biopsy, and 10/127 (7.9%) patients had GG ≥2 disease identified by systematic biopsy but ≤GG1 on targeted biopsy. Significant differences in upgrading on targeted biopsies were seen between sites, likely reflecting different levels of expertise with the targeted biopsy technique.

The addition of MRI with targeted biopsies to systematic biopsies did not significantly increase the upgrading rate compared with systematic biopsy alone. Furthermore, 2-core targeted biopsies alone resulted in a nonsignificant trend to less upgrading than 12-core systematic biopsy (p=0.09). In men on active surveillance, targeted biopsies identify most, but not all, clinically significant cancers.