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Recent studies have shown that alterations of the androgen receptor (AR) are associated with resistance to AR-directed therapy in prostate cancer. Thus, it is crucial to develop robust detection methods for AR alterations as predictive biomarkers to enable applicability in clinical practice. We designed and validated five multiplex droplet digital PCR (ddPCR) assays for reliable detection of 12 AR targets including AR amplification, AR-V7 and 10 AR hotspot mutations as well as AR and KLK3 gene expression from plasma derived cell-free (cf)DNA and cfRNA.The assays demonstrated excellent analytical sensitivity and specificity ranging from 95% to 100% (95% CI: 75-100%). Intra- and inter-run variation analyses revealed a high level of repeatability and reproducibility. The developed assays were further applied in peripheral blood samples from 77 patients with advanced prostate cancer to assess their feasibility in a real-world scenario. Optimizing the reverse transcription of RNA increased the yield of plasma-derived cfRNA by 30-fold. Among 23 patients with castration-resistant prostate cancer (CRPC), 6 patients (26.1%) had one or a combination of several AR alterations, while only 2 out of 54 patients (3.7%) in the hormone-sensitive stage showed AR alterations. These findings were consistent with other studies and suggest that implementation of a comprehensive AR status detection in clinical practice is feasible and can support the treatment decision-making process.
Stitz et al. (Fri,) studied this question.