Cell-free nucleic acids in body fluids as biomarkers for the prediction and early detection of recurrent head and neck cancer: A systematic review of the literature

Accuracy of Salivary Circulating Tumor Human Papillomavirus DNA in Detecting Oropharyngeal Cancer: A Systematic Review and Meta-Analysis

Importance

Circulating tumor human papillomavirus DNA (ctHPV DNA) has shown potential as a biomarker capable of improving outcomes in patients with HPV-related oropharyngeal (OP) cancer. It can be isolated from plasma or saliva, with the latter offering reduced invasiveness and theoretic reduction of lead time.

Objective

To perform a systematic review and meta-analysis on the accuracy of salivary ctHPV DNA for detecting HPV-associated OP cancer.

Data Sources

Cochrane Library, Embase, PubMed, and Web of Science databases were searched from inception through October 2023.

Study Selection

All patients who underwent salivary ctHPV DNA testing at presentation for possible or diagnosed HPV-related OP cancer were included. Non-English and review publications were excluded. Two authors independently voted on article inclusion with a third resolving conflicting votes.

Data Extraction and Synthesis

Following Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guidelines, multiple authors independently abstracted data and assessed bias of included articles. Bivariate random-effects meta-analysis was performed with I2 to assess for study heterogeneity.

Main Outcomes and Measures

Sensitivities, specificities, positive likelihood ratios (PLR), negative likelihood ratios (NLR), and diagnostic odds ratios (DOR) with 95% CIs alongside area under the curve (AUC) of a summary receiver operating characteristic (SROC) curve were calculated. The initial analysis took place throughout December 2023.

Results

Of 440 initially identified articles, 6 met inclusion criteria and demonstrated moderate heterogeneity (I2 = 36%) with low risk of bias and low applicability concerns. Overall, 263 total patients were included with a median (range) age of 58 (39-86) years, and 228 (87%) were male patients. Per updated prognostic staging criteria, localized tumors (ie, stages 1 or 2) comprised most cancers at 139 (77%), whereas advanced ones (ie, stages 3 or 4) comprised the remaining 41 (23%). Pooled sensitivity, specificity, PLR, NLR, and DOR values were 64% (95% CI, 36%-85%), 89% (95% CI, 46%-99%), 11.70 (95% CI, 0.37-77.00), 1.21 (95% CI, 0.08-7.00), and 139.00 (95% CI, 0.05-837.00), respectively. The AUC of the SROC curve was 0.80.

Conclusions and Relevance

This study supports salivary ctHPV DNA as an acceptably specific test in detecting HPV-associated OP cancer that would benefit from testing in clinical trials prior to real-time implementation.

Determinants of the level of circulating-tumor HPV16 DNA in patients with HPV-associated oropharyngeal cancer at the time of diagnosis

Circulating tumor HPV DNA (ctHPV16) assessed in liquid biopsy may be used as a marker of cancer in patients with HPV-associated oropharyngeal cancer (HPV + OPC). Factors influencing the initial ctHPV16 quantity are not well recognized. In this study we aimed to establish what factors are related to the level of ctHPV16 at the time of diagnosis. 51 patients (37 men and 14 women, median age of 57 years old) with HPV + OPC prior to definitive treatment were included. ctHPV16 was measured by qPCR. Tumor and nodal staging were assessed according to AJCC8. Blood derived factors included squamous cell carcinoma antigen (SCC-Ag), serum soluble fragment of cytokeratin 19 (CYFRA 21-1), C-reactive protein (CRP), albumin level (Alb), neutrophils (Neut), thrombocytes (Plt) and lymphocyte (Lym) count, Neut/Lym ratio were assessed. The volumes of the primary tumor (TV) and involved lymph nodes (NV) were calculated using MRI, CT or PET-CT scans. Data were analysed using parametric and nonparametric methods. Variables for multivariable linear regression analysis were chosen based on the results from univariable analysis (correlation, univariable regression and difference). There were 9 (18%), 10 (19%) and 32 (63%) patients who had TV and NV assessed in MRI, CT or PET respectively. Primary tumor neither as T-stage nor TV was related to ctHPV16 level. Significant differences in the ctHPV16 between patients with high vs low pain (P = 0.038), NV (P = 0.023), TV + NV (P = 0.018), CYFRA 21-1 (P = 0.002), CRP (P = 0.019), and N1 vs N3 (P = 0.044) were observed. ctHPV16 was significantly associated with CYFRA 21-1 (P = 0.017), N stage (P = 0.005), NV (P = 0.009), TV + NV (P = 0.002), CRP (P = 0.019), and pain (P = 0.038). In univariable linear regression analysis the same variables predicted ctHPV16 level. In multivariable analyses, CYFRA 21-1 and CRP (both as categorical variables) were predictors of ctHPV16 level even above NV. ctHPV16 at presentation is driven by tumor volume measured mostly by N. CYFRA 21-1 and CRP are additional factors related to ctHPV16 prior to the treatment.

Identification of a serum-based microRNA signature that detects recurrent oral squamous cell carcinoma before it is clinically evident

BACKGROUND

Survival rates for oral squamous cell carcinoma (OSCC) have remained poor for decades, a fact largely attributable to late-stage diagnoses and high recurrence rates. We report analysis of serum miRNA expression in samples from patients with high-risk oral lesions (HRL, including OSCC/carcinoma in situ lesions) and healthy non-cancer controls, with the aim of non-invasively detecting primary or recurrent disease before it is clinically evident.

METHODS

Discovery, test, and validation sets were defined from a total of 468 serum samples (305 HRL and 163 control samples). Samples were analysed using multiple qRT-PCR platforms.

RESULTS

A two-miRNA classifier comprised of miR-125b-5p and miR-342-3p was defined following discovery and test analyses. Analysis in an independent validation cohort reported sensitivity and specificity of ~74% for this classifier. Significantly, when this classifier was applied to serial serum samples taken from patients both before treatment and during post-treatment surveillance, it identified recurrence an average of 15 months prior to clinical presentation.

CONCLUSIONS

These results indicate this serum miRNA classifier is effective as a simple, non-invasive monitoring tool for earlier detection of recurrent disease when lesions are typically smaller and amenable to a wider array of treatment options to improve survival.

Early Diagnosis of Oral Cancer and Lesions in Fanconi Anemia Patients: A Prospective and Longitudinal Study Using Saliva and Plasma

Fanconi anemia (FA) patients display an exacerbated risk of oral squamous cell carcinoma (OSCC) and oral potentially malignant lesions (OPMLs) at early ages. As patients have defects in their DNA repair mechanisms, standard-of-care treatments for OSCC such as radiotherapy and chemotherapy, give rise to severe toxicities. New methods for early diagnosis are urgently needed to allow for treatment in early disease stages and achieve better clinical outcomes. We conducted a prospective, longitudinal study wherein liquid biopsies from sixteen patients with no clinical diagnoses of OPML and/or OSCC were analyzed for the presence of mutations in cancer genes. The DNA from saliva and plasma were sequentially collected and deep-sequenced, and the clinical evaluation followed over a median time of approximately 2 years. In 9/16 FA patients, we detected mutations in cancer genes (mainly TP53) with minor allele frequencies (MAF) of down to 0.07%. Importantly, all patients that had mutations and clinical follow-up data after mutation detection (n = 6) developed oral precursor lesions or OSCC. The lead-time between mutation detection and tumor diagnosis ranged from 23 to 630 days. Strikingly, FA patients without mutations displayed a significantly lower risk of developing precursor lesions or OSCCs. Therefore, our diagnostic approach could help to stratify FA patients into risk groups, which would allow for closer surveillance for OSCCs or precursor lesions.

Practical Application of Circulating Tumor-Related DNA of Human Papillomavirus in Liquid Biopsy to Evaluate the Molecular Response in Patients with Oropharyngeal Cancer

Recent findings have shown that human papillomavirus (HPV) DNA is present in the blood as a tumor-specific biomarker (circulating tumor-related HPV; ctHPV) in patients with HPV-related oropharyngeal cancer (HPV-related OPC). The molecular response (MR) in patients with HPV-related OPC can be defined as the change in the number of ctHPV copies in relation to its initial quantity. The optimal model for assessing the MR using a liquid biopsy (LB) should be based on the E6/E7 sequences of the viral genome. MR assessment can help to evaluate the intensity of ongoing treatments in relation to the tumor response. The evaluation of the residual disease at the end of therapy may also be performed by MR assessment. If a partial MR (pMR) is found, caution is indicated and a subsequent LB should be considered, due to the likelihood of disease progression. Complete radiological and clinical responses together with a complete MR (cMR) convincingly indicate a low risk of treatment failure. Moreover, molecular recurrence (Mrec) during a follow-up, confirmed in two consecutive assays, even despite the lack of any other clinical or radiological symptoms of progression, indicates patients at high risk of disease recurrence. In conclusion, MR by ctHPV assessment may hasten the early detection of disease progression, at any stage of the management of the patient with HPV-related OPC.

HPV and head and neck cancers: Towards early diagnosis and prevention

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide with an increasing trend of its incidence. Alcohol consumption, smoking, and viral infections, such as the mucosal high-risk (HR) human papillomaviruses (HPVs) are major risk factors for HNSCC development. In particular, HR HPVs are mainly associated with a subset of oropharyngeal squamous cell carcinoma (OPSCC), while other head and neck sites are marginally affected by HPV infection. HPV16 is the most frequently HR HPV type associated with HNSCC. In contrast to the cervix, no screening programs or identifiable pre-malignant lesions have been characterized for HPV-related HNSCC. Therefore, identification of general diagnostic algorithms and HPV biomarkers that could facilitate the early diagnosis, disease evolution and recurrence for HPV-driven HNSCCs are urgently needed. We herein review the role of HPV in HNSCC with a focus on epidemiology, biology, applied diagnostic algorithms and available biomarkers in body fluids as early diagnostic tools in HPV-driven HNSCCs.

The COMPLETE trial: HolistiC early respOnse assessMent for oroPharyngeaL cancEr paTiEnts; Protocol for an observational study

INTRODUCTION

The locoregional failure (LRF) rate in human papilloma virus (HPV)-negative oropharyngeal squamous cell carcinoma (OPSCC) remains disappointingly high and toxicity is substantial. Response prediction prior to or early during treatment would provide opportunities for personalised treatment. Currently, there are no accurate predictive models available for correct OPSCC patient selection. Apparently, the pivotal driving forces that determine how a OPSCC responds to treatment, have yet to be elucidated. Therefore, the holistiC early respOnse assessMent for oroPharyngeaL cancer paTiEnts study focuses on a holistic approach to gain insight in novel potential prognostic biomarkers, acquired before and early during treatment, to predict response to treatment in HPV-negative patients with OPSCC.

METHODS AND ANALYSIS

This single-centre prospective observational study investigates 60 HPV-negative patients with OPSCC scheduled for primary radiotherapy (RT) with cisplatin or cetuximab, according to current clinical practice. A holistic approach will be used that aims to map the macroscopic (with Intra Voxel Incoherent Motion Diffusion Kurtosis Imaging (IVIM-DKI); before, during, and 3 months after RT), microscopic (with biopsies of the primary tumour acquired before treatment and irradiated ex vivo to assess radiosensitivity), and molecular landscape (with circulating tumour DNA (ctDNA) analysed before, during and 3 months after treatment). The main end point is locoregional control (LRC) 2 years after treatment. The primary objective is to determine whether a relative change in the mean of the diffusion coefficient D (an IVIM-DKI parameter) in the primary tumour early during treatment, improves the performance of a predictive model consisting of tumour volume only, for 2 years LRC after treatment. The secondary objectives investigate the potential of other IVIM-DKI parameters, ex vivo sensitivity characteristics, ctDNA, and combinations thereof as potential novel prognostic markers.

ETHICS AND DISSEMINATION

The study was approved by the Medical Ethical Committee of Erasmus Medical Center. The main results of the trial will be presented in international meetings and medical journals.

TRIAL REGISTRATION NUMBER

NL8458.

A Systematic Review of Oral Biopsies, Sample Types, and Detection Techniques Applied in Relation to Oral Cancer Detection

Background: Early identification of the stage of oral cancer development can lead to better treatment outcomes and avoid malignant transformation. Therefore, this review aims to provide a comprehensive overview that describes the development of standardized procedures for oral sample collection, characterization, and molecular risk assessment. This can help investigators to choose the appropriate sampling method and downstream analyses for different purposes. Methods: This systematic review was conducted according to the PRISMA guidelines. Using both PubMed and Web of Science databases, four independent authors conducted a literature search between 15 and 21 June 2021. We used key search terms to broaden the search for studies. Non-conforming articles were removed using an EndNote-based and manual approach. Reviewers used a designed form to extract data. Results: This review included a total of 3574 records, after eliminating duplicate articles and excluding papers that did not meet the inclusion criteria. Finally, 202 articles were included in this review. We summarized the sampling methods, biopsy samples, and downstream analysis. The biopsy techniques were classified into tissue and liquid biopsy. The common sequential analysis of tissue biopsy includes histopathological examination such as H&E or IHC to identify various pathogenic features. Meanwhile, liquid samples such as saliva, blood, and urine are analyzed for the purpose of screening to detect mutations in cancer. Commonly used technologies are PCR, RT-PCR, high-throughput sequencing, and metabolomic analysis. Conclusions: Currently, tissue biopsies provide increased diagnostic value compared to liquid biopsy. However, the minimal invasiveness and convenience of liquid biopsy make it a suitable method for mass screening and eventual clinical adoption. The analysis of samples includes histological and molecular analysis. Metabolite analysis is rising but remains scarce.

Diagnostic Value of Salivary miRNA in Head and Neck Squamous Cell Cancer: Systematic Review and Meta-Analysis

Several studies have highlighted the diagnostic potential of salivary microRNA (miRNA) in head and neck squamous cell cancer (HNSCC). The purpose of this meta-analysis was to summarize published studies and evaluate the diagnostic accuracy of salivary miRNA in HNSCC detection. In this meta-analysis, we systematically searched PubMed, EMBASE, and Cochrane Library databases for studies on miRNA and HNSCC diagnosis. Pooled sensitivity, specificity, and diagnostic odds ratio (DOR) with a summary receiver-operating characteristic curve were calculated using a bivariate random-effect meta-analysis model. Furthermore, subgroup analyses were conducted to explore the main sources of heterogeneity. Seventeen studies from ten articles, including 23 miRNA and a total of 759 subjects, were included in this meta-analysis. The pooled sensitivity and specificity of salivary miRNA in the diagnosis of HNSCC were 0.697 (95% CI: 0.644–0.744) and 0.868 (95% CI: 0.811–0.910), respectively. The overall area under the curve was 0.803 with a DOR of 12.915 (95% CI: 9.512–17.534). Salivary miRNAs are a promising non-invasive diagnostic biomarker with moderate accuracy for HNSCC. These results must be verified by large-scale prospective studies.

Coupling size exclusion chromatography to ultracentrifugation improves detection of exosomal proteins from human plasma by LC-MS

Objectives

Exosomes are small lipid bilayer vesicles that are defined by their endocytic origin and size range of 30–140 nm. They are constantly produced by different cell types, by both healthy and abnormal cells, and can be isolated from almost all body fluids.

Little information exists in isolating exosomes from plasma due to the complexity of its content and the presence of contaminating plasma proteins.

Design and methods

We carried-out liquid chromatography-mass spectrometry (LC-MS/MS) analyses of plasma-derived vesicles from 4 healthy donors obtained by 2 coupled methodologies: Ultracentrifugation (UC) coupled with size-exclusion chromatography (SEC) to isolate and subsequently enrich exosomes.

We compared the proteins detected by UC alone and UC coupled with SEC.

Results

In the coupled UC + SEC methodology we found 52.25% more proteins enriched in exosomes as CD9, Annexins, YWHAZ (14-3-3 family) and others, than by using UC alone. There is also a reduction of 98.8% of contaminating plasma proteins by coupling UC and SEC in comparison to using UC alone.

Conclusions

We conclude that exosomes can be successfully isolated from plasma using a very simple combination of standard methods, which could largely improve the proteomics profiling of plasma exosomes.

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Isolating exosomes with the least possible contaminants is very important for their clinical application.

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Isolating exosomes from human plasma faces considerable challenges.

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There is no ideal single isolation technique until this date.

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Exosomes can be successfully isolated from plasma using a combination of Ultracentrifugation and SEC.

Recent advances in point-of-care diagnostics for oral cancer

Early-stage diagnosis is a crucial step in reducing the mortality rate in oral cancer cases. Point-of-care (POC) devices for oral cancer diagnosis hold great future potential in improving the survival rates as well as the quality of life of oral cancer patients. The conventional oral examination followed by needle biopsy and histopathological analysis have limited diagnostic accuracy. Besides, it involves patient discomfort and is not feasible in resource-limited settings. POC detection of biomarkers and diagnostic adjuncts has emerged as non- or minimally invasive tools for the diagnosis of oral cancer at an early stage. Various biosensors have been developed for the rapid detection of oral cancer biomarkers at the point-of-care. Several optical imaging methods have also been employed as adjuncts to detect alterations in oral tissue indicative of malignancy. This review summarizes the different POC platforms developed for the detection of oral cancer biomarkers, along with various POC imaging and cytological adjuncts that aid in oral cancer diagnosis, especially in low resource settings. Various immunosensors and nucleic acid biosensors developed to detect oral cancer biomarkers are summarized with examples. The different imaging methods used to detect oral tissue malignancy are also discussed herein. Additionally, the currently available commercial devices used as adjuncts in the POC detection of oral cancer are emphasized along with their characteristics. Finally, we discuss the limitations and challenges that persist in translating the developed POC techniques in the clinical settings for oral cancer diagnosis, along with future perspectives.

Circulating HPV DNA in the Management of Oropharyngeal and Cervical Cancers: Current Knowledge and Future Perspectives

Human papillomaviruses (HPVs) are associated with invasive malignancies, including almost 100% of cervical cancers (CECs), and 35–70% of oropharyngeal cancers (OPCs). HPV infection leads to clinical implications in related tumors by determining better prognosis and predicting treatment response, especially in OPC. Currently, specific and minimally invasive tests allow for detecting HPV-related cancer at an early phase, informing more appropriately therapeutical decisions, and allowing for timely disease monitoring. A blood-based biomarker detectable in liquid biopsy represents an ideal candidate, and the use of circulating HPV DNA (ct-DNA) itself could offer the highest specificity for such a scope. Circulating HPV DNA is detectable in the greatest part of patients affected by HPV-related cancers, and studies have demonstrated its potential usefulness for CEC and OPC clinical management. Unfortunately, when using conventional polymerase chain reaction (PCR), the detection rate of serum HPV DNA is low. Innovative techniques such as droplet-based digital PCR and next generation sequencing are becoming increasingly available for the purpose of boosting HPV ct-DNA detection rate. We herein review and critically discuss the most recent and representative literature, concerning the role of HPV ctDNA in OPC and CEC in the light of new technologies that could improve the potential of this biomarker in fulfilling many of the unmet needs in the clinical management of OPC and CEC patients.

Association Between Interleukin-6 and Head and Neck Squamous Cell Carcinoma: A Systematic Review

Interleukin-6 (IL-6) is a proinflammatory cytokine which plays an important role in several regulatory mechanisms of cancer. Moreover, experimental and clinical studies have reported that IL-6 targeted therapies might provide significant benefits for cancer treatment. The purpose of this systematic review is to evaluate IL-6 activity in patients with head and neck squamous cell carcinoma (HNSCC). A systematic review of the association between serum, saliva and tumor IL-6 and HNSCC was developed on PubMed/Medline in the publication range from January 1995 to January 2019. Our literature analysis demonstrated that overexpression and elevated serum and/or saliva IL-6 concentrations in patients with HNSCC are related to poor survival and oncological outcomes. Although there is a correlation between IL-6 concentrations and tumorigenicity, it is noteworthy that IL-6 targeted therapies are generally performed in vitro and in experimental studies. Therefore, prospective, randomized clinical trials are required that focus on IL-6 targeted therapies for the treatment of HNSCC.

Pre-analytical issues in liquid biopsy – where do we stand?

It is well documented that in the chain from sample to the result in a clinical laboratory, the pre-analytical phase is the weakest and most vulnerable link. This also holds for the use and analysis of extracellular nucleic acids. In this short review, we will summarize and critically evaluate the most important steps of the pre-analytical phase, i.e. the choice of the best control population for the patients to be analyzed, the actual blood draw, the choice of tubes for blood drawing, the impact of delayed processing of blood samples, the best method for getting rid of cells and debris, the choice of matrix, i.e. plasma vs. serum vs. other body fluids, and the impact of long-term storage of cell-free liquids on the outcome. Even if the analysis of cell-free nucleic acids has already become a routine application in the area of non-invasive prenatal screening (NIPS) and in the care of cancer patients (search for resistance mutations in the EGFR gene), there are still many unresolved issues of the pre-analytical phase which need to be urgently tackled.

Current applications and challenges of circulating tumor DNA (ctDNA) in squamous cell carcinoma of the head and neck (SCCHN)

Liquid biopsies (LB) are emerging in the oncology field, with promising data as new diagnostic, prognostic and treatment-monitoring tools. Squamous cell carcinoma of the head and neck (SCCHN) is a heterogenous disease and many challenges remain to improve patient outcomes. Liquid biopsy could be of interest at different stages of SCCHN disease, including better screening to diagnose more patients at an early stage, early detection of relapse after curative treatment, and the implementation of precision medicine. As LB is very attractive by the ease of sampling, this field is moving fast. Therefore, it is important to be aware of the potential applications but also the limitations of these new tools in regards to technical aspects and interpretation of the data. In this review, we will first give an overview of potential clinical applications and technical challenges of circulating tumor DNA (ctDNA) and then focus on current available data of ctDNA in SCCHN. Although the literature on ctDNA analysis for SCCHN is scarce compared to other tumors, preliminary results seem to hold promise for the future, including the detection of minimal residual disease or the detection of potentially targetable events through liquid biopsy. Prospective liquid-biopsy driven clinical trials are needed to validate its clinical relevance.

Circulating Tumor DNA for Early Cancer Detection

BACKGROUND

Cancer cells release circulating tumor DNA (ctDNA) into the bloodstream, which can now be quantified and examined using novel high-throughput sequencing technologies. This has led to the emergence of the "liquid biopsy," which proposes to analyze this genetic material and extract information on a patient's cancer using a simple blood draw.

CONTENT

ctDNA has been detected in many advanced cancers. It has also been proven to be a highly sensitive indicator of relapse and prognosis. Sequencing the genetic material has also led to the discovery of mutations targetable by existing therapies. Although ctDNA screening is more expensive, it is showing promise against circulating tumor cells and traditional cancer biomarkers. ctDNA has also been detected in other bodily fluids, including cerebrospinal fluid, urine, saliva, and stool. The utility of ctDNA for early cancer detection is being studied. However, a blood test for cancer faces heavy obstacles, such as extremely low ctDNA concentrations in early-stage disease and benign mutations caused by clonal hematopoiesis, causing both sensitivity and specificity concerns. Nonetheless, companies and academic laboratories are highly active in developing such a test.

CONCLUSION

Currently, ctDNA is unlikely to perform at the high level of sensitivity and specificity required for early diagnosis and population screening. However, ctDNA in blood and other fluids has important clinical applications for cancer monitoring, prognosis, and selection of therapy that require further investigation.

Plasma circulating tumor DNA as a potential tool for disease monitoring in head and neck cancer

BACKGROUND

Recommendations for perioperative therapy in head and neck cancer are not explicit and recurrence occurs frequently. Circulating tumor DNA is an emerging cancer biomarker, but has not been extensively explored for detection of recurrence in head and neck cancer.

METHODS

Patients diagnosed with head and neck squamous cell carcinoma were recruited into the study protocol. Tumors were sequenced to identify patient-specific mutations. Mutations were then identified in plasma circulating tumor DNA from pre-treatment blood samples and longitudinally during standard follow-up. Circulating tumor DNA status during follow-up was correlated to disease recurrence.

RESULTS

Samples were taken from eight patients. Tumor mutations were verified in seven patients. Baseline circulating tumor DNA was positive in six patients. Recurrence occurred in four patients, two of whom had detectable circulating tumor DNA prior to recurrence.

CONCLUSION

Circulating tumor DNA is a potential tool for disease and recurrence monitoring following curative therapy in head and neck cancer, allowing for better prognostication, and/or modification of treatment strategies.

Liquid biopsy: miRNA as a potential biomarker in oral cancer

Oral cancer is one of the leading cancers in South-Asian countries. Despite the easy access of the oral cavity, the detection and five year survival rates of OSCC patients are dismal. Identification of non-invasive biomarkers to determine the progression and recurrence of OSCC could be of immense help to patients. Recent studies on oral cancer suggest the importance of non-invasive biomarker development. Micro-RNAs (miRNAs) are one of the important components of the cell-free nucleic acids available in different body fluids. Here, we have reviewed the current understanding of circulating miRNAs as non-invasive biomarkers in different body fluids of oral cancer patients. A number of circulating miRNAs are found to be common in the body fluids of OSCC patients, while many of these are study specific, the possible sources of this variability could be due to differences in sample processing, assay procedure, clinical stage of the disease, oral habit and environmental factors. The prognostic and therapeutic significance of these circulating miRNAs are suggested by several studies. Mir-371, mir-150, mir-21 and mir-7d were found to be potential prognostic markers, while mir-134, mir-146a, mir-338 and mir-371 were associated with metastases. The prognostic markers, mir-21 and mir-7d were also found to be significantly correlated with resistance to chemotherapy, while mir-375, mir-196 and mir-125b were significantly correlated with sensitivity to radiotherapy. Despite the promising roles of circulating miRNAs, challenges still remain in unravelling the exact regulation of these miRNAs before using them for targeted therapy.

Liquid Biopsy in Oral Cancer

Oral cancer is one of the most prevalent forms of cancer worldwide. Carcinogenesis is a complex process, in which heterogeneity plays an important role in the development and progression of the disease. This review provides an overview of the current biological and clinical significance of circulating tumour cells (CTCs), circulating tumour DNA (ctDNA), and exosomes for diagnosis and prognosis of oral cancer. We highlight the importance of liquid biopsy—using blood and saliva—which represents a potential alternative to solid biopsy for diagnosis and prognosis. Moreover, liquid biomarkers allow for the real-time monitoring of tumour evolution and therapeutic responses, initiating the era of personalized medicine. However, in oral cancer, the impact of liquid biopsies in clinical settings is still limited, requiring further studies to discover the best scenario for its clinical use.