Negative Prebiopsy Magnetic Resonance Imaging and Risk of Significant Prostate Cancer: Baseline and Long-Term Followup Results.

PURPOSE: Prostate biopsy should be discussed with the patient in cases of negative magnetic resonance imaging and low clinical suspicion of prostate cancer.Our primary objective was to describe the risk of clinically significant prostate cancer in a negative magnetic resonance imaging biopsy naïve population at baseline and during long-term followup. The secondary objective was to evaluate clinical factors and prostate specific antigen as predictors of clinically significant prostate cancer at baseline.

MATERIALS AND METHODS: All 503 consecutive patients who were biopsy naïve referred from 2007 to 2017 for biopsy with negative magnetic resonance imaging (PI-RADS™ 1-2) who had systematic 12-core biopsies at baseline were included. Clinical factors were digital rectal examination, prostate cancer family history and prostate specific antigen. In case of suspicious digital rectal examination or prostate specific antigen kinetics during followup, magnetic resonance imaging and biopsy were performed. Clinically significant prostate cancer was defined as either Gleason Grade 1 with cancer core length greater than 5 mm or 3 or more positive systematic 12-core biopsies in addition to Gleason Grade 2 or greater (clinically significant prostate cancer-1) or any Gleason Grade 2 or greater (clinically significant prostate cancer-2). Nonclinically significant prostate cancer was defined as either Gleason Grade 1 with cancer core length 5 mm or less and fewer than 3 positive systematic 12-core biopsies (nonclinically significant prostate cancer-1) or any Gleason Grade 1 (nonclinically significant prostate cancer-2). Definition of high risk clinically significant prostate cancer was Gleason Grade 3 or greater. Univariate and multivariate models were fitted to identify predictors of clinically significant prostate cancer risk.

RESULTS: At baseline, biopsy showed clinically significant prostate cancer-1 in 9% (45), clinically significant prostate cancer-2 in 6% (29) and nonclinically significant prostate cancer in 22% (111). At median followup of 4 years (IQR 1.6-7.1), 31% (95% CI 27-36) of 415 untreated patients had a second magnetic resonance imaging and 24% (95% CI 20-28) a second biopsy that showed clinically significant prostate cancer-1 in 5% (21/415, 95% CI 3-7), clinically significant prostate cancer-2 in 2% (7/415, 95% CI 1-3) and nonclinically significant prostate cancer in 8%. Overall incidence was 13% (66/503, 95% CI 7-21) for clinically significant prostate cancer-1, 7% (36/503, 95% CI 5-9%) for clinically significant prostate cancer-2 and 2% (12/503, 95% CI 1.1-3.7) for high risk prostate cancer. Predictors of clinically significant prostate cancer risk were prostate specific antigen density 0.15 ng/ml/ml or greater (OR 2.43, 1.19-4.21), clinical stage T2a or greater (OR 3.32, 1.69-6.53) and prostate cancer family history (OR 2.38, 1.10-6.16). Performing biopsy in patients with negative magnetic resonance imaging and prostate specific antigen density 0.15 ng/ml/ml or greater or abnormal digital rectal examination or prostate cancer family history would have decreased from 9% to 2.4% the risk of missing clinically significant prostate cancer-1 at baseline while avoiding biopsy in 56% of cases.

CONCLUSIONS: The risk of clinically significant prostate cancer in a negative magnetic resonance imaging biopsy naïve population was 6% to 9% at baseline and 7% to 13% at long-term followup depending on clinically significant prostate cancer definitions.