Clinical and molecular determinants of PSA response to bipolar androgen therapy in prostate cancer.

BACKGROUND: Bipolar androgen therapy (BAT) is a novel therapy known to be effective in a subset of men with metastatic castrate resistant prostate cancer (mCRPC). A better understanding of responders and nonresponders to BAT would be useful to clinicians considering BAT therapy for patients. Herein we analyze clinical and genetic factors in responders/nonresponders to better refine our understanding regarding which patients benefit from this innovative therapy. METHODS: mCRPC patients were assessed for response or no response to BAT. Patients with PSA declines of greater than 50% from baseline after 2 or more doses of testosterone were considered to be responders. Whereas, nonresponders had no PSA decline after 2 doses of testosterone and subsequently manifest a PSA increase of >50%. Differences between these two groups of patients were analyzed using clinical and laboratory parameters. All patients underwent genomic testing using circulating tumor DNA (ctDNA) and germline testing pre-BAT. RESULTS: Twenty five patients were nonresponders and 16 were responders. Baseline characteristics between nonresponders and responders varied. Responders were more likely to have had a radical prostatectomy as definitive therapy and were more likely to have been treated with an androgen receptor (AR) antagonist (enzalutamide or apalutamide) immediately before BAT (compared to abiraterone). Duration of prior enzalutamide therapy was longer in responders. Nonresponders were more likely to have bone-only metastases and responders were more likely to have nodal metastases. Assays detected ctDNA AR amplifications more often in responding patients. Responders trended toward having the presence of more TP53 mutations at baseline. CONCLUSIONS: BAT responders are distinct from nonresponders in several ways however each of these distinctions are imperfect. Patterns of metastatic disease, prior therapies, duration of prior therapies, and genomics each contribute to an understanding of patients that will or will not respond. Additional studies are needed to refine the parameters that clinicians can utilize before choosing among the numerous treatment alternatives available for CRPC patients.