Liquid biopsies have become a convenient tool in cancer diagnostics, real-time disease monitoring, and evaluation of residual disease. Yet, the information still encrypted in the variety of tumor-derived molecules identified in biofluids has proven difficult to decipher due to the technological limitations imposed by their biological nature. Such is the case of extracellular vesicle (EV) encapsulated ncRNAs, which have gained traction in recent years as biomarkers. Due to their resilience towards degrading factors they may act as suitable disease indicators. This review addresses the less described issues in this context. We present an overview of less investigated biofluids that can be used for EV isolation in addition to different isolation approaches to overcome the technical challenges these specimens harbor. Furthermore, we summarize the latest technological advances providing improvement to ncRNA detection and analysis. Thereby, this review summarizes the current state-of-the-art methodologies regarding EV and EV derived miRNA analysis and how they compare to current approaches.

Non-coding RNAs (ncRNAs) are essential players in many cellular processes, from normal development to oncogenic transformation. Initially, ncRNAs were defined as transcripts that lacked an open reading frame (ORF). However, multiple lines of evidence suggest that certain ncRNAs encode small peptides of less than 100 amino acids. The sequences encoding these peptides are known as small open reading frames (smORFs), many initiating with the traditional AUG start codon but terminating with atypical stop codons, suggesting a different biogenesis. The ncRNA-encoded peptides (ncPEPs) are gradually becoming appreciated as a new class of functional molecules that contribute to diverse cellular processes, and are deregulated in different diseases contributing to pathogenesis. As multiple publications have identified unique ncPEPs, we appreciated the need for assembling a new web resource that could gather information about these functional ncPEPs. We developed FuncPEP, a new database of functional ncRNA encoded peptides, containing all experimentally validated and functionally characterized ncPEPs. Currently, FuncPEP includes a comprehensive annotation of 112 functional ncPEPs and specific details regarding the ncRNA transcripts that encode these peptides. We believe that FuncPEP will serve as a platform for further deciphering the biologic significance and medical use of ncPEPs. The link for FuncPEP database can be found at the end of the Introduction Section.

Circulating tumor DNA (ctDNA) is the cornerstone of liquid biopsy diagnostics, revealing clinically relevant genomic aberrations from blood of cancer patients. Genomic analysis of single circulating tumor cells (CTCs) could provide additional insights into intra-patient heterogeneity, but it requires whole-genome amplification (WGA) of DNA, which might introduce bias. Here, we describe a novel approach based on mass spectrometry for mutation detection from individual CTCs not requiring WGA and complex bioinformatics pipelines. After establishment of our protocol on tumor cell line-derived single cells, it was validated on CTCs of 33 metastatic melanoma patients and the mutations were compared to those obtained from tumor tissue and ctDNA. Although concordance with tumor tissue was superior for ctDNA over CTC analysis, a larger number of mutations were found within CTCs compared to ctDNA ( p = 0.039), including mutations in melanoma driver genes, or those associated with resistance to therapy or metastasis. Thus, our results demonstrate proof-of-principle data that CTC analysis can provide clinically relevant genomic information that is not redundant to tumor tissue or ctDNA analysis.

The mutational landscape of phylogenetically ultraconserved elements (UCEs), especially those in noncoding DNAs (ncUCEs), and their functional relevance in cancers remain poorly characterized. Here, we perform a systematic analysis of whole-genome and in-house targeted UCE sequencing datasets from more than 3000 patients with cancer of 13,736 UCEs and demonstrate that ncUCE somatic alterations are common. Using a multiplexed CRISPR knockout screen in colorectal cancer cells, we show that the loss of several altered ncUCEs significantly affects cell proliferation. In-depth functional studies in vitro and in vivo further reveal that specific ncUCEs can be enhancers of tumor suppressors (such as ARID1B) and silencers of oncogenic proteins (such as RPS13). Moreover, several miRNAs located in ncUCEs are recurrently mutated. Mutations in miR-142 locus can affect the Drosha-mediated processing of precursor miRNAs, resulting in the down-regulation of the mature transcript. These results provide systematic evidence that specific ncUCEs play diverse regulatory roles in cancer.

Circulating tumor cells (CTCs) can serve as a liquid biopsy to gain insight into treatment responses and metastatic recurrence. Due to their rarity, the analysis of CTCs is challenging and commonly based on immunomagnetic technologies using antibodies against EpCAM. This study used mass cytometry (CyTOF®) for the identification and characterization of CTCs from longitudinally monitored metastatic breast cancer (mBC) patients. Functional analysis focused on DNA damage responses, particularly the DNA repair pathway of homologous recombination (HR) validated in BC cells from the pleura. Fifty‐two blood samples from 13 mBC patients were collected for the enumeration of CTCs using CellSearch® technology, isolation of CTCs together with peripheral blood mononuclear cells (PBMCs) and of plasma. Cell‐free DNA (cfDNA) from plasma was analyzed by shallow genome sequencing to determine tumor fraction (TF) and HR deficiency (HRD). CTC/PBMC mixtures were phenotyped by CyTOF® using a panel of 13 antibodies including anti‐γH2AX, 53BP1, and RAD51. CyTOF® identified CTCs correlating with CellSearch®‐ and cfDNA‐based quantifications, detected DNA damage in CTCs, and the dynamics of their HR status during genotoxic therapies. Our study shows that CyTOF®‐based phenotyping of CTCs from mBC patients shows promise as a method to monitor tumor progression and HR proficiency in real time for the identification of chemoresistance.

Circulating tumor cells (CTCs) are valuable liquid biopsy analytes as they facilitate an in‐depth characterization of disseminated tumors by a simple blood draw. Most CTC assays can only process limited blood volumes, potentially hampering the detection of cells of very low frequency, such as CTCs. Here, we introduce a novel, functionalized nickel filtration membrane, facilitating rapid enrichment of CTCs from various volumes of blood up to 40 mL and leukapheresis products. We validated this assay with different cancer cell lines and compared the performance of our new assay with that of the FDA‐cleared CellSearch® system. Performing a comparative analysis of 20 blood samples from patients with metastatic breast cancer, CTCs were found in 19/20 patients (95%), combining the results of both CTC enrichment assays. CTC counts/7.5 mL of blood ranged from 0 to 7280 (CTC filtration membrane) and 0 to 17,190 (CellSearch®). Applying the clinically relevant cut‐off of ≥5 CTCs/7.5 mL of blood, 19/20 samples processed with our CTC filter were categorized identically to those analyzed with the CellSearch® system. Furthermore, the filtration time of 40 s for 7.5 mL of blood represents an important advantage of our system, compared to other systems. Importantly, we also demonstrated the feasibility of processing blood samples of up to 40 mL or 2 × 10 ⁸ nucleated blood cells in 2.5 min. Overall, our new system provides the advantage of performing ultra‐rapid enrichment of CTCs and upscaling the volume of blood that can be analyzed, which opens a new avenue for studies on CTC biology.