Prostate Cancer Predictor at Low PSA prostate biopsy. In this case, however, the sensitivity is 67.5% to 80%, but the specificity is only 20% to 30% [5,6]. The incidence of prostate cancer in patients with PSA ＜4 ng/ml has been known to be approximately 15%. It was re- ported that biopsy-detected prostate cancer, including high-grade cancers, is not rare among men with PSA levels of 4 ng/ml or less [7,8]. Until now, however, the criteria for performing a prostate biopsy on patients with PSA ＜4 ng/ml have not been established clinically. 　Many studies have been conducted on the intermediate- PSA group with PSA in the range of 4-10 ng/ml. On the other hand, only a few studies on the predictive factors for pro- state cancer in prostate biopsy have been conducted in pa- tients with PSA ＜4 ng/ml. Furthermore, no comprehensive analysis of various variables stratified with the PSA level has been reported so far in Korea. 　Accordingly, this study was conducted to investigate the predictive factors for prostate cancer in patients with PSA equal to or less than 4 ng/ml, by analyzing the correlation of the variables with the results of the biopsy. MATERIALS AND METHODS A retrospective study of medical records was conducted on 292 patients with initial serum PSA ≤4 ng/ml among 2,305 patients who underwent a transrectal ultrasound-guided prostate needle biopsy at Korea University hospital from January 2003 to December 2008. A prostate needle biopsy was performed on patients with PSA ≤4 ng/ml in cases of abnormal findings in the digital rectal examination (DRE) or transrectal ultrasonography (TRUS) or on patients with a PSA level higher than the age-adjusted PSA level. Abnor- mal DRE findings were defined as palpable induration, nodularity, irregularity, or asymmetry. Abnormal TRUS findings were defined as capsular irregularity, deforma- tion, or existence of a hypoechoic region. PSA was meas- ured by using enzyme immunoassay, and it was measured before the DRE or TRUS to minimize interference. 　For the reference value of the age-adjusted PSA, 1.88 ng/ml for people in their 30s, 1.92 ng/ml for people in their 40s, 2.37 ng/ml for people in their 50s, 3.56 ng/ml for people in their 60s, and 5.19 ng/ml for people in their 70s were used, according to the study of Jeon et al [9]. The prostate volume was calculated by measuring the height, width, and length by using TRUS and by subsequently putting such figures into the ellipsoid formula of 3.14/6x(height)x(width) x(length). The 12-core biopsy scheme used in our insti- tution includes a standard sextant, which was originally described by Hodge et al [10], as well as a lateral sextant scheme (lateral apex, lateral mid-gland, lateral base) [11]. The biopsy policy of our institution consists of an additional two core biopsies in cases of palpable nodules in the DRE or suspicious lesions in TRUS. Biopsies were performed un- der ultrasound guidance by use of an 18-gauge, 2 cm, Trucut core needle biopsy. 　The patients were divided into a group diagnosed with prostate cancer and the non-prostate-cancer group accord- 167 ing to prostate needle biopsy. Subsequently, the age, pros- tate volume, PSA, PSA density (PSAD: the ratio of total PSA to prostate volume), percentage of free PSA (%fPSA: free PSA/total PSA ratio), International Prostate Symp- tom Score (IPSS), maximal flow rate, and abnormal find- ings in the DRE and TRUS of the two groups were com- pared. In addition, the PSA level was divided into ranges of 0.0-1.9 ng/ml, 2.0-2.9 ng/ml, and 3.0-4.0 ng/ml, followed by analysis. 　In the prostate cancer group and the non-prostate-can- cer group, the age, prostate volume, PSA, PSAD, %fPSA, IPSS, and maximal flow rate were compared by using the Student’s t-test. The abnormal findings in the DRE and TRUS were compared by using the Pearson’s chi-square test. In addition, to identify the predictive factors for pros- tate cancer in a prostate needle biopsy, a multiple logistic regression analysis was conducted. As a result of this anal- ysis, potential predictive factors for prostate cancer were identified. Their diagnostic validity was evaluated by re- ceiver operating characteristic (ROC) curve analysis. SPSS ver. 12.0 (SPSS Inc., Chicago, IL, USA) software was used for the statistical analysis. MedCalc ver. 11.4.3 (MedCalc Software, Mariakerke, Belgium) software was used to com- pare the area under the curve (AUC) of each predictive factor with the ROC curve. In all cases of hypothesis testing, two- sided testing was used, and probability values (p-values) of less than 0.05 were considered statistically significant. RESULTS Of the 2,305 patients who underwent a prostate needle bi- opsy, 292 had a PSA ≤4 ng/ml. The mean age of the patients was 63.1 years old; their prostate volume, 37.3 cc; their PSA, 2.9 ng/ml; their PSAD, 0.08 ng/ml/cc; their %fPSA, 0.23; their IPSS, 15.6; their maximal flow rate, 15.16 ml/s; and the frequencies of abnormal findings in the DRE and TRUS, 36.9% and 31.5%, respectively. 　For the patients with PSA ≤4 ng/ml, when the prostate cancer group (n=28) was compared with the non-prostate- cancer group (n=264), no significant differences in prostate volume (33.8 vs. 37.7 cc), PSA (3.0 vs. 2.9 ng/ml), PSAD (0.10 vs. 0.08 ng/ml/cc), %fPSA (0.18 vs. 0.23), IPSS (17.8 vs. 15.4), maximal flow rate (12.8 vs. 15.4 ml/s), frequency of palpable lesions in the DRE (14.2% vs. 11.3%), or fre- quency of hypoechoic lesions in the TRUS (42.8% vs. 30.3%) were found between the two groups in the univariate and multivariate analyses, respectively. On the other hand, mean age was significantly higher in the prostate cancer group than in the normal group (66.9 vs. 62.7 years old, p=0.033 in univariate analysis, p=0.034 in multivariate analysis, odds ratio=1.052) (Table 1). The diagnostic val- idity based on age was low, however, and the AUC in the ROC curve was only 0.607 (95% confidence interval [CI]: 0.507-0.707). 　Of the 28 prostate cancer patients, 25 patients (89%) had a Gleason score of 6 or less, 1 patient (4%) had a score of 7, and 2 patients (7%) had a score of 8 or above. Korean J Urol 2011;52:166-171