To the Editor: Antonarakis and colleagues (Sept. 11 issue) 1 reported a significant association between the presence of androgen-receptor splice variant 7 messenger RNA (AR-V7) in circulating tumor cells and shorter prostate-specific antigen (PSA) progression–free survival, clinical or radiographic progression–free survival, and overall survival in men with metastatic castration-resistant prostate cancer who were treated with enzalutamide or abiraterone. Several treatment options (abiraterone, enzalutamide, sipuleucel-T, and radium-223) have recently been shown to prolong survival in men with metastatic castration-resistant prostate cancer who have not previously been treated with chemotherapy; the identification of reliable biomarkers that can predict response should optimize treatment with these approaches. A study by Loriot and colleagues 2 suggests that the duration of sensitivity to previous androgen-deprivation therapy (ADT) is predictive of the efficacy of subsequent endocrine manipulations in patients with castrationresistant prostate cancer. Loriot et al. found that 58% of patients with a duration of sensitivity to previous therapy of at least 16 months had a PSA response to subsequent treatment, as compared with 18% of patients with a duration of sensitivity of less than 16 months (P = 0.01). Antonarakis et al. observed no PSA response to abiraterone or enzalutamide in men who tested positive for AR-V7. We wonder about the relationship between AR-V7 positivity and the duration of response to previous ADT.
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A 2014 study studied this question.