Serum testosterone level is a useful biomarker for determining the optimal treatment for castration-resistant prostate cancer.

Our aim was to evaluate the usefulness of serum testosterone to guide treatment decision for castration-resistant prostate cancer (CRPC).

We conducted a retrospective analysis of 115 patients with CRPC treated with either abiraterone (n = 43) or enzalutamide (n = 72). A serum testosterone level was measured at time of starting of abiraterone or enzalutamide. We determined whether serum testosterone influenced the outcomes of androgen receptor (AR)-targeted therapy.

In the very-low testosterone group (<5 ng/dl), the rate of prostate-specific antigen (PSA) response was significantly higher among patients treated with abiraterone compared to enzalutamide (62 vs. 32%, respectively; P = 0.033), with no difference in the low testosterone group (5-<50 ng/dl) (93 vs. 81%, respectively; P = 0.429). During the median follow-up of 26 months, PSA progression-free survival was significantly longer in the low testosterone group than in the very-low testosterone group (12.2 vs. 4.5 months, P<0.001). In the very-low testosterone group, enzalutamide use (HR 3.07, 95% CI 1.36-6.94; P = 0.007), primary androgen deprivation therapy <12 months (HR 2.50, 95% CI 1.23-5.08; P = 0.011) and bone metastases (HR 2.60, 95% CI 1.20-5.64; P = 0.015) were significantly associated with PSA progression.

Patients with a serum testosterone level ≥5 ng/dl were more likely to receive therapeutic benefits from AR-targeted therapy compared to those with serum testosterone levels <5 ng/dl. However, even for those with a very low serum testosterone level, the efficacy of abiraterone was slightly higher than that of enzalutamide. Therefore, serum testosterone level is a useful biomarker for informing treatment selection for CRPC.

Urologic oncology. 2019 May 16 [Epub ahead of print]

Kohei Hashimoto, Hidetoshi Tabata, Tetsuya Shindo, Toshiaki Tanaka, Jiro Hashimoto, Ryuta Inoue, Takashi Muranaka, Hiroshi Hotta, Masahiro Yanase, Yasuharu Kunishima, Atsushi Takahashi, Naoya Masumori, Sapporo Medical University Urologic Oncology Consortium (SUOC)

Department of Urology, Sapporo Medical University School of Medicine, Chuo-ku, Sapporo, Japan., Department of Urology, Asahikawa Redcross Hospital, Asahikawa, Japan., Department of Urology, Sunagawa City Medical Center, Sunagawa, Hokkaido, Japan., Department of Urology, Hakodate Goryoukaku Hospital, Hakodate, Japan., Department of Urology, Sapporo Medical University School of Medicine, Chuo-ku, Sapporo, Japan. Electronic address: .

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