Plasma total RNAs as prognostic biomarkers in metastatic prostate cancer: integration with immune deconvolution using cibersortx LM22

Metastatic castration-resistant prostate cancer (mCRPC) represents the terminal stage of prostate cancer progression and remains a major clinical challenge despite therapeutic advances with androgen receptor signaling inhibitors (ARSIs) such as abiraterone and enzalutamide. To date, the absence of robust biomarkers capable of predicting treatment response limits the implementation of personalized therapeutic strategies. The present study aimed to investigate the prognostic role of plasma-derived total RNA, with a particular focus on circular RNAs (circRNAs), as novel liquid biopsy biomarkers in patients with mCRPC, and to explore their integration with immune deconvolution using CIBERSORTx. A prospective multicenter cohort of 100 mCRPC patients treated with first-line ARSIs was analyzed. Total cell-free RNA (cfRNA) was isolated from plasma and subjected to high-throughput RNA sequencing. Differential expression analysis and immune transcriptomic deconvolution were performed to identify molecular signatures associated with clinical outcome. High-quality cfRNA libraries were successfully generated, confirming the feasibility of comprehensive transcriptomic profiling from plasma. Expression of canonical prostate cancer genes (AR, ERG, MYC, KLK3) validated tumor signal detectability. Several mRNAs (CLEC4G, CYP2E1, GALNT3) were upregulated in long-responders, whereas others (HNGB1P10, FCGR2A, SOCS2) and five circRNAs (circKMT2E, circRMDN3, circPCCB, circZSWIM6, circODF2) were enriched in short-responders. Immune deconvolution revealed higher levels of CD4⁺ memory resting T cells in long-responders and significant correlations between circRNA expression and immune subsets. These findings demonstrate that cfRNA and circRNA profiling provides valuable insights into tumor biology and host immune status, supporting their potential as complementary liquid biopsy biomarkers in mCRPC management.