Identification of favorable subgroups for alternative anti-androgen therapy in castration-resistant prostate cancer.

Although alternative anti-androgen therapy (switching to secondary anti-androgens) is no longer recommended in the clinical guidelines of prostate cancer in light of the new hormonal and cytotoxic agents available, this therapy has proven beneficial for some patients with castration-resistant prostate cancer (CRPC). The objective of this study was to identify favorable subgroups for alternative anti-androgen therapy among CRPC patients. Eighty-eight consecutive CRPC patients treated with alternative anti-androgen therapy were included in this study. All patients were treated with bicalutamide in the initial maximum androgen blockade (MAB) and switched to flutamide in the subsequent alternative anti-androgen therapy, combined with a luteinizing hormone-releasing hormone analogue. Several clinical and pathological factors for predicting the prostate-specific antigen (PSA) decline and PSA progression-free survival (PSA-PFS) of alternative anti-androgen therapy were investigated. Of all patients, 45 (51.1%) patients showed ≥50% PSA decline. The median PSA-PFS was 7.5 months [95% confidence interval (CI), 5.7-10.3]. Notably, 15 (17.0%) patients had a PSA-PFS over 2 years. A multivariate analysis showed that ≥3 bone metastatic lesions and a duration <12 months of initial MAB were significant factors shortening the duration of PSA-PFS, with hazard ratios of 2.11 (95% CI, 1.23-3.62; P=0.007) and 2.08 (95% CI, 1.20-3.57; P=0.008), respectively. Patients without any of these factors had a median PSA-PFS of 22.8 months (95% CI, 6.7-48.8). The overall survival in patients with a ≥7.5-month PSA-PFS receiving alternative anti-androgen therapy was significantly longer than that of patients with a <7.5-month PSA-PFS (109.1 vs. 40.8 months; P<0.001). In conclusion, a longer duration of initial MAB and the absence of severe bone metastasis may predict a favorable response to alternative anti-androgen therapies in CRPC patients. Alternative anti-androgen therapy may still be beneficial for these patients, but this needs to be investigated further.