Background: Antiandrogens used to treat benign prostatic hyperplasia (BPH) may affect the diagnosis of prostate cancer by decreasing serum prostate-specific antigen (PSA) values. We conducted a retrospective survey of BPH patients treated with chlormadinone acetate (CMA) and analysed the effect of CMA on their PSA values. Methods: A chart-based, retrospective, multi-institutional survey of clinically diagnosed patients with BPH who had been treated with CMA (Prostal; 50 mg/day) was conducted. The patients were divided into three groups according to their baseline PSA values: <4 ng/mL, Group I; ≥4 ng/mL and <10 ng/mL, Group II; and ≥10 ng/mL, Group III. The changes in the PSA values from baseline after 16, 26, and 52 weeks of CMA therapy were predicted using a nonlinear regression model analysis. Results: Data from 192 of the 303 enrolled patients were analysed. The predicted percent changes from baseline among all patients after 16, 26, and 52 weeks of treatment were -49.6%, -49.8%, and -49.9%, respectively. The corresponding values were -42.4%, -43.7% and -43.8% in Group I; -57.4%, -58.4% and -58.5% in Group II; and -50.6%, -50.6% and -50.6% in Group III, respectively. Conclusion: The PSA values reached a nadir, approximately -50% of the baseline, after 16 weeks of CMA administration and remained at the same level thereafter. When CMA is used to treat BPH patients, the possibility of abnormal increases in PSA associated with prostate cancer must be considered; if prostate cancer is suspected, prompt testing, including a biopsy, should be performed.
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