Background: Transrectal ultrasound guided biopsy of the prostate is the most common modality used to diagnose prostate cancer.

Objectives: The aim of this study was to evaluate the optimal number of cores at prostate biopsy, which have the most diagnostic value with least adverse effects.

Patients and materials: Transrectal ultrasonography (TRUS) guided biopsy was performed in 180 patients suspicious for prostate cancer due to either abnormal rectal examination or elevated PSA. The patients were divided randomly into three groups of six-core, twelve-core and eighteen-core biopsies. The detection rate of prostate cancer in each group with the rate of post biopsy urinary infection and prostatitis were compared.

Results: Prostate cancer was diagnosed in 8 (13.3%), 21 (35%) and 24 (40%) patients in six, twelve and eighteen core biopsy groups, respectively. Urinary tract infection and prostatitis occurred in 17 (28.3%), 23 (38.3%) and 35 (58.3%) patients in six, twelve and eighteen core biopsy groups, respectively. Considering the detection rate of prostate cancer, there was a significant difference between 6 and 12 core biopsy groups (P = 0.006) and 12-core biopsies detected more cases of prostate cancer, but there was no significant difference between 12 and 18 core biopsy groups (P = 0.572). Considering the infection rate, there was no significant difference between 6 and 12 core biopsy groups (P = 0.254), but there was a significant difference between 12 and 18 core biopsy groups (P = 0.028) and infectious complications occurred more frequently in 18-core biopsy group.

Conclusions: The best balance between detection rate of prostate cancer and infectious complications of biopsies achieved in twelve-core biopsy protocol. Twelve-core biopsy enhances the rate of prostate cancer detection with minimum adverse effects.