The purpose of active surveillance for suitable patients is to maintain patients’ QOL by deferring or delaying definitive treatment when prostate cancer is unlikely to cause mortality or significant morbidity, while simultaneously ensuring the appropriate potential to implement definitive treatment with curative intent should this become necessary. As such, a critical component of management with active surveillance for patients with newly diagnosed prostate cancer is an assessment of the patient’s risk for harboring more aggressive disease in the prostate than was detected on biopsy, which would thereby render the patient at increased risk for experiencing subsequent disease progression. MRI has been utilized as one such tool for risk assessment in this setting,168, 169 particularly among patients whose initial prostate biopsy was performed without prior MRI guidance. The purported rationale here has been to obtain complete gland imaging, potentially allowing detection of more aggressive disease in the prostate in regions not sampled on the patient’s diagnostic biopsy. Patients with positive MRI findings have been found to be more likely to contain clinically significant disease (typically, higher Grade Group).170 A role for MRI prior to confirmatory biopsy among patients on active surveillance for low-risk prostate cancer was investigated in the prospective, randomized ASIST trial.171 Although the initial report of the trial did not find a statistically significant difference in the rate of biopsy upgrading among patients with versus without a pre-confirmatory biopsy MRI, a follow-up report from the trial found that patients who underwent MRI had fewer active surveillance failures and less grade progression at two years follow-up post biopsy.172 Thus, the Panel believes that an MRI should be obtained if the initial (diagnostic) prostate biopsy was performed without MRI guidance. If the MRI demonstrates findings suspicious for clinically significant prostate cancer (PIRADS 4 or 5), then timely repeat (confirmatory) targeted biopsy is recommended, with disease risk re-established based on these biopsy results. Conversely, if the MRI is assessed as PIRADS 1, 2, or 3, then repeat biopsy may be performed within approximately 12 months after diagnosis. Thereafter, serial surveillance biopsies are recommended every one to four years depending on patient age, health, risk of progression, and preference.168, 173, 174 Evidence for the utility of serial prostate MRI to evaluate for changes in disease risk among patients on surveillance remains mixed; as such, MRI cannot be recommended as a stand-alone replacement for periodic repeat biopsy.175 For example, a cohort study demonstrated that a surveillance strategy using MRI or clinical changes as the sole indicator for repeat biopsy would have missed upgrading to Grade Group 2 or higher in 169 of every 1,000 patients on surveillance, leading to the conclusion by the authors that periodic biopsy should remain a component of the management of patients on surveillance.176 A subsequent meta-analysis found a pooled sensitivity and specificity for detecting Grade Group of 2 or more of 0.59 (95% CI 0.44 to 0.73) and 0.75 (95% CI 0.66 to 0.84), respectively.177 It should be noted that interobserver variability in interpreting MRI may be a limitation. Therefore, while the Panel recognizes that MRI may be utilized in patients electing active surveillance, further study is warranted to determine the optimal timing and incorporation of continued imaging for patient management.