Epigenetic dysregulation is a hallmark of many human malignancies, with DNA methylation being a primary mechanism influencing gene expression and maintaining genomic stability. Genome-wide hypomethylation, characteristic of many cancers, is partly attributed to the demethylation of repetitive elements, including LINE-1, a prevalent non-LTR retrotransposon. The methylation status of LINE-1 is closely associated with overall genomic methylation levels in tumors. cfDNA comprises extracellular DNA fragments found in bodily fluids such as plasma, serum, and urine, offering a dynamic snapshot of the genetic and epigenetic landscape of tumors. This real-time sampling provides a minimally invasive avenue for cancer diagnostics, prognostics, and monitoring. The methylation status of LINE-1 in cfDNA has emerged as a promising biomarker, with several studies highlighting its potential in diagnosing and predicting outcomes in cancer patients. Recent research also suggests that cfDNA-based LINE-1 methylation analysis could serve as a valuable tool in evaluating the efficacy of cancer therapies, including immunotherapy. The growing clinical significance of cfDNA calls for a closer examination of its components, particularly repetitive elements like LINE-1. Despite their importance, the role of LINE-1 elements in cfDNA has not been thoroughly gauged. We aim to address this gap by reviewing the current literature on LINE-1 cfDNA assays, focusing on their potential applications in diagnostics and disease monitoring.

Head and neck squamous cell carcinomas (HNSCCs) that develop from the mucosal epithelium in the oral cavity, pharynx, and larynx are a heterogeneous group of malignant tumors. A lack of appropriate screening and diagnostic methods leads to late diagnoses, with the majority of patients having locally advanced disease, which is associated with a high risk of local recurrence and a poor prognosis and is usually treated with combination therapies. Biomarkers for predicting the therapy response and risk of recurrence in HNSCC patients are urgently needed. Liquid biopsy, e.g., the profiling of circulating biomarkers in bodily fluids, is a promising approach with increasing utility in the early detection and diagnosis of cancer, monitoring cancer progression, patient stratification and treatment selection, detecting minimal residual disease (MRD), and predicting recurrence across different cancer types, including HNSCC. Among liquid biomarkers, circulating tumor DNA (ctDNA), which is based on detecting tumor-specific mutations, insertions/deletions, copy number alterations, and methylation, is the most promising transformative tool in cancer management and personalized cancer treatment. In this review, we provide an update of recent data on the role of non-viral ctDNA in the management of HNSCC patients. Accumulating data suggests the enormous potential of ctDNA profiling by serial sampling during and after definitive therapy in detecting MRD and predicting recurrence in HNSSC patients treated with a single treatment modality (surgery or radiotherapy) or with combination therapies, including immune-checkpoint-inhibitor-based immunotherapy. By incorporating the latest immunotherapy trials and organizing the data by the treatment modality, this review offers a novel perspective not found in previous surveys.

Background: Pericentric human satellite II (HSATII) and III (HSATIII) have been shown to be associated with stress response. Expression status of these satellite repeats has not yet been investigated under radiation-induced genotoxic stress. We evaluated the HSATII and HSATIII expression changes under genotoxic stress in cancer cells. Materials and Methods: ...

Background/Objectives: Liquid profiling of molecular and epigenetic markers in bodily fluids is an expanding field of cancer biomarker research. Recent research activity also reveals the human satellite 2 (HSAT2) repetitive element cell-free DNA (cfDNA) as a potential cancer biomarker. Based on our recent results from targeted sequencing of HSAT2 cfDNA, we tested whether a specific HSAT2 sequence (e.g., 95 bp-HSAT2) shows greater cancer enrichment than 114 bp-SAT2, from which it derives, in patients with colon cancer. Methods: By comparing the ratio of 114 bp-HSAT2 to 95 bp-HSAT2, we investigated the increased cancer enrichment of 95 bp-HSAT2 in cfDNA samples obtained from plasma DNA extraction and a hybridization capture assay, in which HSAT2 sequences were captured from plasma using a biotin-labeled probe, in samples from colon cancer patients (n = 60) and polyp-controls (n = 60), and polyp-free controls (n = 60). Results: A correlation analysis between Ct values from DNA extraction and the hybridization capture assay for both 95 bp- and 114 bp-HSAT2 showed a positive correlation in patients with colon cancer and control subjects, indicating that the hybridization capture assay provides HSAT2 levels comparable to those obtained by DNA extraction. With both approaches, we found a lower 114 bp-HSAT2 to 95 bp-HSAT2 ratio in patients with colon cancer than in the control groups. The median ratio of extracted DNA was 62, 78, and 79 in patients with colon cancer, polyp-controls (p = 0.23), and polyp-free controls (p = 0.067), respectively. Capture assay values were 49, 87, and 64 in patients with colon cancer, polyp controls (p = 0.016), and polyp-free controls (p = 0.19), respectively. Even though statistical significance was not achieved in some comparisons, these results suggest that 95 bp-HSAT2 is more abundant in the blood of patients with colon cancer than 114 bp-HSAT2 in non-malignant patients. Conclusions: To our knowledge, this is the first study to conduct a hybridization capture assay using a biotinylated probe as a feasible approach for targeted enrichment of cfDNA from plasma. Our results confirm the outcomes of our recent article based on targeted sequencing and reveal that some specific HSAT2 sequences may exhibit increased cancer abundance.

Background/Aim: Despite effective screening programs, colorectal cancer (CRC) continues to be an important health burden. Circulating RNAs of various types, which are relatively stable in bodily fluids, have been explored as cancer biomarkers with proven potential in detection, diagnosis, treatment, and patient follow-up, in various cancer types, including CRC. Here, we were interested in the clinical significance of H19 and insulin-like growth factor 2 (IGF2) as circulating RNA biomarkers in CRC, two imprinted genes of the IGF-2/H19 cluster. Materials and Methods: H19 lncRNA and IGF-2 mRNA were quantified in plasma samples of 80 pathologically confirmed, treatment-naïve CRC patients, and 80 CRC-free control subjects, of whom 40 had polyps and 40 others did not. Results: Plasma levels of H19 lncRNA and IGF-2 mRNA were significantly higher in CRC patients than in control subjects; relative median values of H19 lncRNA were 912, 97, and 262 in CRC patients, the polyp controls, and non-polyp controls, respectively (p=0.000135 and p=0.002, respectively). Relative median values of plasma IGF-2 mRNA were 298, 29, and 112 in the above groups, respectively (p<0.001 and p=0.035, respectively. Patients with lymph node metastases had significantly higher H19 lncRNA levels than patients without lymphatic metastases (median values 1474 vs. 196; p=0.05). This association was absent for IGF-2 mRNA. Although not statistically significant, both RNA markers showed a tendency to be associated with larger tumor size and advanced disease stage. Conclusion: Plasma H19 lncRNA and IGF-2 mRNA may be a marker of tumor burden in CRC, while H19 lncRNA is also an indicator of CRC progression, which, if confirmed, can be used in the clinical management of CRC patients.