Measurement of peri-prostatic fat thickness using transrectal ultrasonography (TRUS): a new risk factor for prostate cancer

OBJECTIVE To determine if the amount of periprostatic fat (PPF) on transrectal ultrasonography (TRUS) is a risk factor for incident prostate cancer overall and high-grade prostate cancer (Gleason >= 4). PATIENTS AND METHODS A prospectively maintained database of patients undergoing prostate biopsy at Princess Margaret Hospital for cancer suspicion was used. All TRUS examinations were retrospectively reviewed upon 'blinding' to outcome. PPF thickness, measured as the distance between the prostate and the pubic bone, was used as an index of the quantity of PPF. PPF measurements, together with other prostate cancer risk factors, were evaluated against prostate cancer and high-grade prostate cancer detection upon biopsy with univariable and multivariable logistic regression and area under the receiver operating characteristic curve (AUC) analysis. RESULTS Of the 931 patients, 434 (47%) were diagnosed with prostate cancer and 218 (23%) were diagnosed with high-grade prostate cancer. The mean (range) PPF thickness was 5.3 (0-15) mm. Increasing PPF thickness was associated with prostate cancer and high-grade prostate cancer diagnosis, with graded effect. When adjusting for other variables, the odds of detecting any prostate cancer and high-grade prostate cancer increased 12% (odds ratio [OR] 1.12, 95% confidence interval [CI] 1.02-1.23) and 20% (OR 1.20, 95% CI 1.07-1.34), respectively, for each millimetre increase in PPF thickness. The AUCs for the association of PPF with prostate cancer and high-grade prostate cancer were 0.58 (95% CI 0.54-0.62) and 0.59 (95% CI 0.55-0.64), respectively. CONCLUSION The amount of PPF can be estimated with TRUS and is a predictor of prostate cancer and high-grade prostate cancer at biopsy. To our knowledge, this study is the first to investigate PPF quantity in patients without prior prostate cancer diagnosis.