150 [5]. For localized prostate cancer, radical prostatectomy and radiation therapy have been the recommended treatment modalities [6]. Hormone treatment has been considered a gold standard for the treatment of advanced prostate can- cer [7]. Hormone treatment is a feasible option as the pri- mary treatment of choice for localized prostate cancer, de- pending on the patient’s age at diagnosis, life expectancy, and socioeconomic status [5]. However, after 18 to 24 mon- ths of hormone treatment, advanced prostate cancer pro- gresses to castration-resistant prostate cancer (CRPC) [8]. Therefore, it is important to be able to forecast which pa- tients have cancer that may progress to CRPC in order to improve the efficacy of hormone treatment and to perform additional treatments. Recent studies have reported that changes in the free-to-total PSA (f/t PSA) ratio in patients with advanced prostate cancer whose PSA level has reached the nadir is an important prognostic factor. Therefore, we investigated the pattern of change in the f/t PSA ratio and the pro- gression to CRPC in patients with advanced prostate can- cer who received hormone treatment and whose PSA nadir was below 0.1 ng/ml. MATERIALS AND METHODS We retrospectively analyzed the medical records of 52 pa- tients who received hormone treatment after a diagnosis of advanced prostate cancer between January 2007 and April 2009. Data on age, initial PSA, clinical stage, lymph node metastasis, and bone metastasis were collected. The follow-up data of the patients included PSA, free PSA (fPSA), and f/t PSA ratio every 3 months for 15 months. The 2010 American Joint Committee on Cancer/tumor-node- metastasis staging system and Gleason system were used for the pathologic staging and tumor grading [9]. The clin- ical stage was locally advanced (T3-4) or metastatic (stage T1-4N0-1M1) prostate cancer. The pathologic diagnosis was confirmed with transrectal ultrasonography-guided Kim et al prostate biopsy. All patients underwent magnetic reso- nance imaging and bone scans for staging workup. All patients were treated with maximum androgen blockade (gonadotrophin-releasing hormone agonist and anti-androgen agents) [10]. The patients who underwent radical prostatectomy or radiation therapy before hormone therapy, antiandrogen monotherapy, or other forms of che- motherapy were excluded. According to the European Association of Urology Guideline, CRPC was defined as 2 consecutive increases in PSA despite a testosterone level in the castration range [6]. The PSA nadir was defined as the lowest PSA level during hormone treatment [11,12]. The patients were divided into two groups with a nadir f/t PSA ratio above 60% (group 1) and a nadir f/t PSA ratio of 60% or below (group 2). The pattern of change in the f/t PSA ratio during the course of hormone treatment and pro- gression to CRPC were compared between the two groups. The Mann-Whitney U-test, Fisher exact test, and chi-squ- are test were used to compare the two groups of patients. Kaplan-Meier survival analysis and the log rank test was used to analyze the difference in progression to CRPC be- tween the two groups. All statistical analyses were per- formed with SPSS ver. 18.0 (IBM, New York, NY, USA), and p-values less than 0.05 were determined to be statisti- cally significant. RESULTS Table 1 summarizes the clinical characteristics and CRPC progression in the two groups. The median age of the pa- tients was 75 years (interquartile range [IQR], 70 to 80 years), and the median Gleason score was 7 (IQR, 6 to 9). PSA and the f/t PSA ratio at the time of diagnosis were 16.27 ng/ml (IQR, 9.32 to 88.06 ng/ml) and 8.80% (IQR, 0.01 to 11.50%), respectively. The PSA nadir of all patients was lower than 0.1 ng/ml. The median nadir f/t PSA ratio and the time to PSA nadir were 60% (IQR, 60 to 87%) and 6 months (IQR, 5 to 9 months), respectively. Progression to CRPC occurred in 34 patients, and the median time elapsed TABLE 1. The clinical characteristics and CRPC progression in the two groups Total (n=52) 75 (70-80) 7 (6-9) 16.27 (9.32-88.06) 8.80 (0.01-11) 60 (60-87) 6 (5-9) 7 (13.4) 22 (42.3) 34 (65.3) 15 (12-24) Group 1 (n=24) 75 (55-87) 8 (7-9) 23.53 (6.39-84.02) 10 (2-15) 90 (80-90) 5 (4-8) 3 (12.5) 10 (41.6) 10 (41.6) 15 (12-24) Group 2 (n=28) 75 (70-81) 6 (6-8) 13.73 (9.32-100.00) 6 (0.01-10) 60 (30-60) 7 (6-9) 4 (14.2) 12 (42.8) 24 (85.7) 15 (12-24) p-value 0.713a 0.007a 0.567a 0.283a 0.001a 0.111a 0.654b 0.578b 0.002b 0.792a Characteristic Age (yr) Biopsy Gleason score Initial PSA (ng/ml) Initial f/t PSA ratio (%) Nadir f/t PSA ratio (%) Time to PSA nadir (mo) LN invasion (%) Bone metastasis (%) Progression to CRPC (%) Time to CRPC (mo) Korean J Urol 2012;53:149-153 Values are presented as □ (interquarile range). PSA, prostate-specific antigen; f/t PSA ratio, free-to-total PSA ratio; LN, lymph node; CRPC, castration-resistant prostate cancer. a: Mann-Whitney U-test, b: Fisher exact test and Chi-square test.