Accuracy of Magnetic Resonance Imaging/Ultrasound Fusion Targeted Biopsies to Diagnose Clinically Significant Prostate Cancer in Enlarged Compared to Smaller Prostates

Purpose: We assessed the accuracy of magnetic resonance imaging/transrectal ultrasound fusion biopsies to diagnose prostate cancer according to gland size. Materials and Methods: A prospective study was performed in 232 men with a first round biopsy, multiparametric magnetic resonance imaging with a lesion, a Likert score of 2 or greater and prostate specific antigen less than 10 ng/ml. All men underwent a standard 12-core protocol plus a protocol of 2 or 3 targeted cores. Significant prostate cancer was defined as at least 1 core with a Gleason score of 7 (3 + 4) or 6 with a greater than 4 mm maximal cancer core length. Results: Mean +/- SD patient age was 64 +/- 6.4 years, mean prostate specific antigen was 6.65 +/- 1.8 ng/ml and mean prostate volume was 40 +/- 24.3 ml. The overall detection rate of clinically significant prostate cancer was 44%. The detection rate of clinically significant prostate cancer by magnetic resonance imaging-transrectal ultrasound fusion guided biopsy was 77% for prostate glands less than 30 cm 3, and 61%, 47% and 34% for glands 30 to less than 38.5, 38.5 to less than 55 and 55 to 160 cm(3), respectively (p = 0.001). Differences in prostate cancer detection rates between the standard and targeted protocols were not significant for patients with a prostate volume of 40 cm(3) or less (p = 0.8). Conversely 12 patients with a prostate volume greater than 40 cm(3) had clinically significant prostate cancer using the targeted but not the standard protocol and in 3 prostate cancer was detected by the standard but not the targeted protocol (p = 0.04). Conclusions: Magnetic resonance imaging-transrectal ultrasound fusion biopsies increased the yield of first round prostate biopsies in patients with a prostate volume greater than 40 cm(3).