High concordance of findings obtained from transgluteal magnetic resonance imaging - and transrectal ultrasonography-guided biopsy as compared with prostatectomy specimens

OBJECTIVES: To determine the utility of our transgluteal magnetic resonance imaging (MRI)-guided prostate biopsy approach.

PATIENTS AND METHODS: A total of 960 biopsy series, taken within the period of 1 year, were evaluated, including 301 MRI-guided and 659 transrectal ultrasonography (TRUS)-guided biopsies.

RESULTS: The positivity rate and proportion of high grade cancers were significantly higher in MRI-guided than in TRUS-guided biopsies. Of 301 MRI-guided biopsies, 65.4% contained cancer while 57.2% of 659 TRUS biopsies contained cancer (P = 0.016). Gleason grade 3 + 3 = 6 disease was observed in 16.8% of 197 MRI-guided and in 36.1% of 377 TRUS-guided biopsies (P < 0.001). There was also a markedly higher quantity of cancer tissue in MRI-guided biopsies. In all cancers, the mean cancer surface area was 64.8 ± 51.6 mm2 in MRI-guided biopsies as compared with 23.0 ± 31.4 mm2 in non-MRI-guided biopsies (P < 0.001). With respect to the tissue quantity, superiority of MRI-guided biopsy was highest in Gleason grade 3 + 3 = 6 cancers (20.9 ± 27.9 vs 5.1 ± 10.2 mm2 ; P < 0.001) and in Gleason grade 3 + 4 = 7 cancers (59.7 ± 38.0 vs 17.7 ± 18.4 mm2 ; P < 0.001). Comparison of biopsy Gleason grades with findings in prostatectomy specimens was possible in 80 patients with MRI-guided and in 170 patients with non-MRI-guided biopsies. This comparison showed a very high but almost identical concordance of TRUS- and MRI-guided biopsies with the prostatectomy specimen findings. With both approaches, undetected high-risk cancers were present in ~10% of patients with low-risk biopsy results. A significant difference was observed, however, in the proportion of patients who had clinically insignificant cancers and who underwent surgery. The proportion of patients with Gleason grade 3 + 3 = 6 carcinoma in their prostatectomy specimen was 11.2% in the post-TRUS biopsy cohort, but only 2.5% in the post-MRI biopsy cohort (P = 0.021).

CONCLUSION: MRI-guided transgluteal prostate biopsy has a high detection rate for high-risk carcinomas, while the risk of detecting clinically insignificant carcinomas appears to be reduced. This may by itself lead to a reduction of unnecessary prostatectomies. Overtreatment may be further avoided by better applicability of molecular testing to MRI-guided biopsies because of the excessive amount of tissue available for analysis, especially in patients with potential low-risk carcinomas.