Purpose: We analyzed the pattern of change in the free-to-total prostate-specific antigen (f/t PSA) ratio and the progression to castration-resistant prostate cancer (CRPC) in patients with advanced prostate cancer 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 patients with advanced prostate cancer. All patients were treated with maximum androgen blockade (gonadotrophin-releasing hormone agonist and anti-androgen agents). The patients were divided into two groups: those with a nadir f/t PSA ratio above 60% and those with a nadir f/t PSA ratio of 60% or below. Age, initial PSA, clinical stage, lymph node metastasis, bone metastasis, and follow-up data, including PSA, free PSA, and f/t PSA ratio, were collected. The Mann-Whitney U-test, Fisher exact test, chi-square test, Kaplan-Meier survival analysis, and log rank test were used. Results: There were 24 patients in the group with a nadir f/t PSA ratio above 60% and 28 patients in the group with a nadir f/t PSA ratio of 60% or below. After hormone therapy, the median f/t PSA ratio in each group increased from 37% and 34% at 3 months to 75% and 60% at 6 months, respectively. At 9 months, however, the f/t PSA ratio increased to 80% in the group with a nadir f/t PSA ratio above 60%, whereas it decreased to 31% in the group with a nadir f/t PSA ratio of 60% or below. From 9 to 15 months, the f/t PSA ratio showed a tendency to decrease (75 to 37% and 27 to 20%, respectively). The progression to CRPC was significantly different between the two groups (10 vs. 24). Conclusions: Progression to CRPC was significantly higher in the group with a lower f/t PSA ratio. Additionally, the pattern of change in the f/t PSA ratio was significantly different after 9 months. Collectively, the f/t PSA ratio can be used as an additional marker for prognosis of hormone treatment.
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