Unilateral positive biopsies in low risk prostate cancer patients diagnosed with extended transrectal ultrasound-guided biopsy schemes do not predict unilateral prostate cancer at radical prostatectomy

OBJECTIVE To establish the predictors of unilateral prostate cancer in a population of patients with low risk prostate cancer, diagnosed with extended biopsy and submitted to radical prostatectomy, potentially candidates for focal therapy. PATIENTS AND METHODS The study included 321 consecutive patients with low risk (clinical stage T1, Gleason score 3 + 3 or less, prostate-specific antigen [PSA] < 10 ng/mL) unilateral prostate cancer diagnosed after extended biopsy who were subsequently treated with radical prostatectomy between 2002 and 2009 at a single institution. We evaluated the rate of unilateral prostate cancers at final pathology following radical prostatectomy, defined as pT2a or pT2b stage. Univariable and multivariable logistic regression analyses were used to identify predictors of unilateral prostate cancers. Predictive accuracy was assessed with estimates of the area under the receiver operating characteristic curve, which were subjected to 200 bootstraps to reduce overfit bias. RESULTS At final pathology only 29.3% patients harboured unilateral prostate cancer. No significant differences in terms of age, preoperative PSA, prostate volume and percentage of positive cores were recorded between patients with unilateral prostate cancer and patients with more advanced stage (all P >= 0.07). Patients harbouring unilateral prostate cancer had a smaller number of positive biopsy cores (2.8 vs 3.2, P = 0.056) compared with patients with stage pT2c or higher at final pathology. Patients with unilateral prostate cancer had a higher rate of Gleason sum 6 compared with patients with more advanced pathological stage (pT2c or higher: 85.1% vs 65.6%; P = 0.002). On multivariable analyses, only the percentage of positive cores (odds ratio 0.57; P = 0.047) was an independent predictor of unilateral prostate cancer at radical prostatectomy, after controlling for age, PSA at diagnosis and prostate volume (all P >= 0.3). The newly developed model for identifying the presence of unilateral prostate cancer failed to achieve accurate prediction (area under the curve 52.3%). When only patients with a single positive core were considered, no differences in PSA and prostate volume were detected (all P >= 0.5) and a similar rate of unilateral prostate cancer was demonstrated (33.3% vs 28.4%; P = 0.5). CONCLUSIONS In patients with unilateral low risk prostate cancer at biopsy, only one-third showed unilateral prostate cancer at radical prostatectomy. The number of cores and the number of positive cores represented independent predictors of unilateral prostate cancer. However, the accuracy of the multivariable model in predicting unilateral prostate cancer is low (52.3%), thus making prediction of unilateral prostate cancer extremely inaccurate. These results need to be taken into account in those cases where focal therapy is considered as a treatment of prostate cancer.