Objectives: To evaluate the impact of adding magnetic resonance imaging-ultrasound (MRI-US) fusion biopsy cores to standard 12-core biopsy in selecting men for active surveillance (AS). Materials and Methods: Among men undergoing a fusion biopsy for evaluation of prostate cancer, we selected men who were eligible for at least 1 of 7 different AS criteria based on the standard biopsy alone. We assessed each patient's eligibility for each AS criterion with and without the inclusion of fusion biopsy cores. The primary end point was the proportion of men who were initially eligible for AS but became ineligible after addition of the fusion biopsy cores. Results: A total of 100 men were eligible for at least 1 AS criterion. After addition of fusion biopsy cores, the proportion of men who became ineligible for AS varied from 10.3% to 40.7%. Criteria that incorporated an absolute maximum number of cores positive had the highest rates of ineligibility. Using a percentage of cores positive helped to reduce the number of patients who would have been excluded. Combining the targeted biopsy cores into one, or taking the single core with the highest grade or volume did not appear to reduce the proportion of men who became ineligible. Conclusions: The addition of fusion biopsy to standard 12-core biopsy significantly increased the number of men who became ineligible for AS. Using the percent of cores positive, instead of an absolute number, allowed fewer exclusions. AS criteria may need to be updated to prevent the unnecessary exclusion of men due to an oversampling of low-risk disease.
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