Prostate Cancer Predictor at Low PSA TABLE 3. Characteristics of patients in different total PSA ranges Variable 0.0-1.9 ng/ml No. of patients Age (yr) Prostate vol (cc) PSA (ng/ml) PSAD (ng/ml/cc) %fPSA IPSS Qmax (ml/sec) DRE (＋) TRUS (＋) BPH 42 63.0 32.3 1.36 0.04 0.23 14.8 12.6 9 19 PCa 3 67.0 25.6 1.20 0.05 0.21 18.3 9.1 1 2 p-value 0.542 0.327 0.552 0.531 0.834 0.410 0.402 1.000 0.905 BPH 78 64.7 39.0 2.5 0.07 0.31 15.7 11.8 11 27 Serum PSA range 2.0-2.9 ng/ml PCa 7 71.5 26.9 2.4 0.09 0.15 17.7 15.5 1 4 p-value 0.049a 0.028a 0.522 0.042a 0.665 0.485 0.090 1.000 0.438 BPH 144 61.5 38.5 3.56 0.10 0.19 15.4 18.1 10 34 3.0-4.0 ng/ml PCa 18 65.1 37.8 3.52 0.11 0.19 17.8 12.4 2 6 169 p-value 0.157 0.865 0.592 0.607 0.934 0.235 0.592 0.874 0.541 PSA: prostate-specific antigen, BPH: benign prostatic hyperplasia, PCa: prostate cancer, PSAD: PSA density, %fPSA: percent free PSA, IPSS: International Prostate Symptom Score, Qmax: maximal flow rate, DRE: digital rectal examination, TRUS: transrectal ultra- sonography, a: statistically significant (p＜0.05) FIG. 1. Receiver operating characteristic curve analysis of age, prostate volume, and PSAD with PSA value of 2.0-2.9 ng/ml. PSAD: prostate-specific antigen density, PSA: prostate-specific antigen. TRUS are commonly used to diagnose prostate cancer. The results of such tests show that if the serum PSA level in- creases, or if abnormal findings are observed in the pros- tate in the DRE or TRUS, an ultrasound-guided prostate needle biopsy is performed to confirm the prostate cancer. PSA, a tumor marker of prostate cancer, was initially in- troduced for postoperative follow-up and was gradually used as a screening test, which brought about tremendous change in the morbidity and mortality of prostate cancer. In particular, because prostate cancer is diagnosed during early stages as the result of PSA testing, the number of ad- vanced-stage prostate cancer patients has rapidly de- creased from the late 1980s to the early 1990s [12]. The cut- off value of PSA for prostate cancer diagnosis is still con- troversial, however, and decision-making on the perform- ance of a prostate biopsy on the basis of only the PSA cutoff value has limitations with respect to sensitivity, specific- ity, and positive predictive value. Many studies have been conducted to determine the PSA cutoff value. Catalona et al reported that a PSA level of 4 ng/ml or higher was appro- priate as the PSA cutoff value for the screening of prostate cancer. Since then, this value has been most commonly used clinically; whereas its sensitivity is 67.5-80%, its spe- cificity is only 20-30% [13]. 　In general, the detection rates of prostate cancer based on the PSA level are 10-20% at 2.5-4.0 ng/ml; 25% at 4.1-10.0 ng/ml; and 50-60% at 10 ng/ml or higher [14]. Kobayashi et al reported that the detection rate of prostate cancer was 23.6% both in the group with PSA of 2.0-4.0 ng/ml and in the group with PSA of 4.1-10.0 ng/ml, and no difference in pathological features was found [15]. Park et al also reported that no difference in the detection rate of prostate cancer and its pathological features was found be- tween the group with PSA of 3.0-4.0 ng/ml and the group with PSA of 4.1-10.0 ng/ml [16]. According to the study of Thompson et al, 15.2% of the cases of prostate cancer diag- nosed in prostate biopsy showed normal findings in the DRE, and their PSA level was less than 4 ng/ml. In addition, 14.9% of the prostate cancer turned out to be prostate can- cer with high-grade Gleason score of 7 or higher [8]. According to the study of Kwon et al, normal DRE findings were shown in 55% of patients with a PSA ＜4 ng/ml who underwent a radical prostatectomy, of whom 64% were di- agnosed with prostate cancer at a level higher than a Gleason score of 7 [17]. Therefore, a significant number of patients with PSA ＜4 ng/ml show clinically significant prostate cancer. Many studies reported that good outcomes were obtained from prostate cancer patients with low PSA levels when they underwent a radical prostatectomy [18- 20]. Therefore, some studies have proposed that active screening tests for prostate cancer be conducted on pa- tients with PSA ＜4 ng/ml [21-23]. Catalona et al proposed that the PSA cutoff value be decreased to 2.5 ng/ml to detect prostate cancer early in patients who can be completely cured, because 20% of prostate cancer patients have PSA Korean J Urol 2011;52:166-171