Androgen receptor genomic alterations and treatment resistance in metastatic prostate cancer

Background Genomic alterations to the androgen receptor (AR) are common in metastatic castration-resistant prostate cancer (mCRPC). AR copy number amplifications, ligand-binding domain missense mutations, and intronic structural rearrangements can all drive resistance to approved AR pathway inhibitors and their detection via tissue or liquid biopsy is linked to clinical outcomes. With an increasingly crowded treatment landscape, there is hope that AR genomic alterations can act as prognostic and/or predictive biomarkers to guide patient management. Methods In this review, we evaluate the current evidence for AR genomic alterations as clinical biomarkers in mCRPC, focusing on correlative studies that have used plasma circulating tumor DNA to characterize AR genotype. Results We highlight data that demonstrates the complexity of AR genotype within individual patients, and suggest that future studies should account for cancer clonal heterogeneity and variable tumor content in liquid biopsy samples. Given the potential for cooccurrence of multiple AR genomic alterations in the same or competing subclones of a patient, it is distinctly challenging to attribute blanket clinical significance to any individual alteration. This challenge is further complicated by the varied treatment exposures in contemporary patients, and the fact that AR genotype continues to evolve in the mCRPC setting across sequential lines of systemic therapy. Conclusions As treatment access and liquid biopsy technology continues to improve, we posit that real-time measures of AR biology are likely to play a key role in emerging precision oncology strategies for metastatic prostate cancer.