Introduction: Prostate cancer (PCa) is one of the most common malignancies in men and a major cause of cancer deaths among men worldwide. Prostate specific antigen (PSA) monitoring and histopathological examination of tumor biopsies remain gold standards in PCa diagnostics. These clinical parameters are not well suited for patient stratification, predicting and monitoring treatment response. On the other hand, liquid biopsies offer a unique opportunity to easily isolate tumor-derived material for longitudinal clinical assessment. Areas covered: In this review we focus on the clinical application of novel liquid biomarkers that have the potential to monitor and stratify patients in order to achieve better therapeutic effects and improve clinical outcomes. Enumeration and characterization of circulating tumor cells (CTCs), tumor-educated platelets, exosomes, and cell-free nucleic acids have been studied for their clinical utility in PCa diagnostics, prognostics, monitoring treatment response and guiding treatment choice. Expert opinion: Liquid biomarkers have high potential to be used for prognosis, monitoring treatment response and guiding treatment selection. Although there is a remarkable progress in PCa biomarker discovery, their clinical validation is very limited. Research should be focused on biomarker validation and the incorporation of these biomarkers in clinical practice.
Background Several treatment options were recently added for metastatic castration-resistant prostate cancer (mCRPC). However, response to therapy is variable, and biomarkers that can guide treatment selection and response evaluation are lacking. Circulating RNAs are a promising source of biomarkers. We explored messenger RNAs (mRNAs), microRNAs (miRNAs), and long noncoding RNAs (lncRNAs) as potential biomarkers in liquid biopsies of patients with mCRPC treated with enzalutamide. Methods Forty patients were included in this prospective multicenter observational study. Whole blood was drawn at baseline and 1, 3, and 6 months after start of therapy. Four mRNAs, 6 miRNAs, and 5 lncRNAs were analyzed by quantitative PCR. RNA levels in 30 healthy individuals were used as controls. RNA expression data were analyzed by Kaplan–Meier and Cox regression analyses, and the primary end point was progression-free survival. Clinical factors were included in the multivariable Cox regression analysis. Results Levels of 2 miRNAs, miR-375 and miR-3687, and 1 lncRNA, N-acetylated alpha-linked acidic dipeptidase like 2 antisense RNA 2 (NAALADL2-AS2), were more than 2-fold higher in patients with mCRPC compared with healthy volunteers. Patients with higher levels of miR-375 or miR-3687 showed a shorter time to progression. Patients with higher levels of NAALADL2-AS2 showed a longer time to progression. In the multivariable Cox regression analysis, higher miR-375, miR-3687 and serum prostate-specific antigen concentrations were shown to be independent predictors for shorter time to progression. Conclusions We identified miR-3687 as a novel prognostic marker for response in patients with CRPC treated with enzalutamide, and we confirmed the prognostic value of miR-375.
Circulating RNAs extracted from liquid biopsies represent a promising source of cancer and therapy-related biomarkers. We screened whole blood from patients with metastatic castration-resistant prostate cancer (mCRPC) following their first-line treatment with abiraterone acetate and prednisone (AA-P) to identify circulating RNAs that may correlate with progression free survival (PFS).In a prospective multi-center observational study, 53 patients with mCRPC were included after they started first-line AA-P treatment. Blood was drawn at baseline, one, three and six months after treatment initiation.The levels of pre-defined circulating RNAs earlier identified as being upregulated in patients with mCRPC (e.g. microRNAs, long non-coding RNAs and messenger RNAs), were analyzed. Uni-and multi-variable Cox regression and Kaplan-Meier analyses were used to analyze the prognostic value of the various circulating RNAs for PFS along treatment.Detectable levels of KLK3 mRNA at baseline were demonstrated to be an independent prognostic marker for PFS (201 vs 501 days, P=0.00054). Three months after AA-P treatment initiation, KLK3 could not be detected in the blood of responding patients, but was still detectable in 56% of the patients with early progression.Our study confirmed that KLK3 mRNA detection in whole blood is an independent prognostic marker in mCRPC patients receiving AA-P treatment. Furthermore, the levels of circulating KLK3 mRNA in patients receiving AA-P treatment might reflect treatment response or early signs of progression.
The clinical utility of circulating tumor cells (CTC) as a non-invasive multipurpose biomarker is broadly recognized. The earliest methods for enriching CTCs from whole blood rely on antibody-based positive selection. The prognostic utility of CTC enumeration using positive selection with the FDA-approved CellSearchTM system has been demonstrated in numerous studies. The capture of cells with specific protein phenotypes does not fully represent cancer heterogeneity and therefore does not realize the prognostic potential of CTC liquid biopsies. To avoid this selection bias, CTC enrichment based on size and deformability may provide better fidelity, i.e., facilitate the characterization of CTCs with any phenotype. In this study, the recently FDA-approved Parsortix® technology was used to enrich CTCs from prostate cancer (PCa) patients for transcriptome analysis using HyCEADTM technology. A tailored PCa gene panel allowed us to stratify metastatic castration-resistant prostate cancer (mCRPC) patients with clinical outcomes. In addition, our findings suggest that targeted CTC transcriptome profiling may be predictive of therapy response.
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