The ratio of the number of biopsy specimens to prostate volume (biopsy density) > 1.5 improves the prostate cancer detection rate in men undergoing transperineal biopsy of the prostate.

Purpose: We sought to determine the minimum number of transperineal prostate mapping biopsies needed to optimize the prostate cancer detection rate. Materials and Methods: A total of 436 men underwent transperineal prostate mapping biopsy at 2 institutions. Biopsy density was calculated as the ratio of the total number of specimens retrieved (mean 59.4) to prostate volume (mean 44.9 cc). Associations of biopsy density with prostate specific antigen, prostate specific antigen density, cancer diagnosis and the Gleason score were tested by ANOVA and the chi-square test. Regression analysis was done to determine factors associated with a positive transperineal prostate mapping biopsy and Gleason score 7 or higher cancer. Results: Transperineal prostate mapping biopsy was positive in 299 of 436 men (68.6%). The mean number of positive cores was 7.1 (range 1 to 41) and mean biopsy density was 1.46 (range 0.39 to 3.67). The mean number of cores in positive vs negative transperineal prostate mapping biopsies was 1.61 vs 1.14 (p < 0.001). Biopsy density cut points of 0.5 or less, greater than 0.5 to 1.0, greater than 1.0 to 1.5 and greater than 1.5 were associated with positive biopsy in 25%, 37.4%, 70.7% and 84.9% of patients (p < 0.001). Dichotomizing biopsy density to 1.5 or less vs greater than 1.5 resulted in a positive biopsy rate of 56.4% vs 84.9% (OR 1.5, 95% CI 1.3-1.7, p < 0.001). More Gleason score 6 cancers were diagnosed with higher biopsy density (94 of 158 or 59.5% vs 62 of 141 or 44.9%, p = 0.007). However, the number of positive cores with Gleason score 6 was greater in men with higher biopsy density at 4.9 vs 3.6 (p = 0.036). Prostate specific antigen (p = 0.053) and biopsy density (p = 0.012) were significant on regression analysis for positive transperineal prostate mapping biopsy and Gleason score 7+ disease. Conclusions: Biopsy density greater than 1.5 increases the diagnosis of prostate cancer by 1.5 times, detects higher volume Gleason score 6 disease and should be considered the optimal sampling approach when performing transperineal prostate mapping biopsy.