Circulating tumor DNA in liquid biopsy: Current diagnostic limitation

With the rapid development of science and technology,cell-free DNA(cfDNA)is rapidly becoming an important biomarker for tumor diagnosis,monitoring and prognosis,and this cfDNA-based liquid biopsy technology has great potential to become an important part of precision medicine.cfDNA is the total amount of free DNA in the systemic circulation,including DNA fragments derived from tumor cells and all other somatic cells.Tumor cells release fragments of DNA into the bloodstream,and this source of cfDNA is called circulating tumor DNA(ctDNA).cfDNA detection has become a major focus in the field of tumor research in recent years,which provides a new opportunity for non-invasive diagnosis and prognosis of cancer.In this paper,we discuss the limitations of the study on the origin and dynamics analysis of ctDNA,and how to solve these problems in the future.Although the future faces major challenges,it also con-tains great potential.

Circulating tumor cells and circulating tumor DNA in breast cancer diagnosis and monitoring

Liquid biopsy,including both circulating tumor cells and circulating tumor DNA,is becoming more popular as a diagnostic tool in the clinical management of breast cancer.Elevated concentrations of these biomarkers during cancer treatment may be used as markers for cancer progression as well as to understand the mechanisms underlying metastasis and treatment resistance.Thus,these circulating markers serve as tools for cancer assessing and monitoring through a simple,non-invasive blood draw.However,despite several study results currently noting a potential clinical impact of ctDNA mutation tracking,the method is not used clinically in cancer diagnosis among patients and more studies are required to confirm it.This review focuses on understanding circulating tumor biomarkers,especially in breast cancer.

Liquid biopsy in patients with pancreatic cancer: Circulating tumor cells and cell-free nucleic acids

Despite recent advances in surgical techniques and perioperative management, the prognosis of pancreatic cancer(PCa) remains extremely poor. To provide optimal treatment for each patient with Pca, superior biomarkers are urgently needed in all phases of management from early detection to staging, treatment monitoring, and prognosis. In the blood of patients with cancer, circulating tumor cells(CTCs) and cell-free nucleic acids(cf NAs), such as DNA, m RNA, and noncoding RNA have been recognized. In the recent years, their presence in the blood has encouraged researchers to investigate their potential use as novel blood biomarkers, and numerous studies have demonstrated their potential clinical utility as a biomarker for certain types of cancer. This concept, called "liquid biopsy" has been focused on as a less invasive, alternative approach to cancer tissue biopsy for obtaining genetic and epigenetic aberrations that contribute to oncogenesis and cancer progression. In this article, we review the available literature on CTCs and cfN As in patients with cancer, particularly focusing on PCa, and discuss future perspectives in this field.

Circulating tumor DNA as a liquid biopsy target for detection of pancreatic cancer

Most pancreatic cancer patients present with advanced metastatic disease, resulting in extremely poor 5-year survival, mainly because of the lack of a reliable modality for early detection and limited therapeutic options for advanced disease. Therefore, there is a need for minimally-invasive diagnostic tools for detecting pancreatic cancer at an early stage, when curative surgery and also novel therapeutic approaches including precision medicine may be feasible. The "liquid biopsy" addresses these unmet clinical needs based on the concept that simple peripheral blood sampling and detection of circulating tumor DNA(ct DNA) could provide diagnostic information. In this review, we provide an overview of the current status of bloodbased tests for diagnosis of pancreatic cancer and the potential utility of ct DNA for precision medicine. We also discuss challenges that remain to be addressed in developing practical ct DNA-based liquid biopsy approaches for early diagnosis of pancreatic cancer.

Liquid biopsy in patients with hepatocellular carcinoma: Circulating tumor cells and cell-free nucleic acids

Hepatocellular carcinoma(HCC), with its high incidence and mortality rate, is one of the most common malignant tumors. Despite recent development of a diagnostic and treatment method, the prognosis of HCC remains poor. Therefore, to provide optimal treatment for each patient with HCC, more precise and effective biomarkers are urgently needed which could facilitate a more detailed individualized decision-making during HCC treatment, including the following; risk assessment, early cancer detection, prediction of treatment or prognostic outcome. In the blood of cancer patients, accumulating evidence about circulating tumor cells and cell-free nucleic acids has suggested their potent clinical utilities as novel biomarker. This concept, so-called "liquid biopsy" is widely known as an alternative approach to cancer tissue biopsy. This method might facilitate a more sensitive diagnosis and better decision-making by obtaining genetic and epigenetic aberrations that are closely associated with cancer initiation and progression. In this article, we review recent developments based on the available literature on both circulating tumor cells and cell-free nucleic acids in cancer patients, especially focusing on Hepatocellular carcinoma.

Liquid biopsy of gastric cancer patients:Circulating tumor cells and cell-free nucleic acids

To improve the clinical outcomes of cancer patients,early detection and accurate monitoring of diseases are necessary.Numerous genetic and epigenetic alterations contribute to oncogenesis and cancer progression,and analyses of these changes have been increasingly utilized for diagnostic,prognostic and therapeutic purposes in malignant diseases including gastric cancer(GC).Surgical and/or biopsy specimens are generally used to understand the tumor-associated alterations;however,those approaches cannot always be performed because of their invasive characteristics and may fail to reflect current tumor dynamics and drug sensitivities,which may change during the therapeutic process.Therefore,the importance of developing a non-invasive biomarker with the ability to monitor real-time tumor dynamics should be emphasized.This concept,so called"liquid biopsy",would provide an ideal therapeutic strategy for an individual cancer patient and would facilitate the development of"tailor-made"cancer management programs.In the blood of cancer patients,the presence and potent utilities of circulating tumor cells(CTCs)and cell-free nucleic acids(cfNAs)such as DNA,mRNA and microRNA have been recognized,and their clinical relevance is attracting considerable attention.In this review,we discuss recent developments in this research field as well as the relevance and future perspectives of CTCs and cfNAs in cancer patients,especially focusing on GC.

Circulating tumor DNA dynamics analysis in a xenograft mouse model with esophageal squamous cell carcinoma

BACKGROUND It remains unclear which factors,such as tumor volume and tumor invasion,influence circulating tumor DNA(ctDNA),and the origin of ctDNA in liquid biopsy is always problematic.To use liquid biopsies clinically,it will be very important to address these questions.AIM To assess the origin of ctDNA,clarify the dynamics of ctDNA levels,assess ctDNA levels by using a xenograft mouse after treatment,and to determine whether tumor volume and invasion are related to ctDNA levels.METHODS Tumor xenotransplants were established by inoculating BALB/c-nu/nu mice with the TE11 cell line.Groups of mice were injected with xenografts at two or four sites and sacrificed at the appropriate time point after xenotransplantation for ctDNA analysis.Analysis of ctDNA was performed by droplet digital PCR,using the human telomerase reverse transcriptase(hTERT)gene.RESULTS Mice given two-site xenografts were sacrificed for ctDNA at week 4 and week 8.No hTERT was detected at week 4,but it was detected at week 8.However,in four-site xenograft mice,hTERT was detected both at week 4 and week 6.These experiments revealed that both tumor invasion and tumor volume were asso ciated with the detection of ctDNA.In resection experiments,hTERT was detected at resection,but had decreased by 6 h,and was no longer detected 1 and 3 d after resection.CONCLUSION We clarified the origin and dynamics of ctDNA,showing that tumor volume is an important factor.We also found that when the tumor was completely resected,ctDNA was absent after one or more days.

Liquid biopsy for gastric cancer:Techniques,applications,and future directions

After the study of circulating tumor cells in blood through liquid biopsy(LB),this technique has evolved to encompass the analysis of multiple materials originating from the tumor,such as nucleic acids,extracellular vesicles,tumor-educated platelets,and other metabolites.Additionally,research has extended to include the examination of samples other than blood or plasma,such as saliva,gastric juice,urine,or stool.LB techniques are diverse,intricate,and variable.They must be highly sensitive,and pre-analytical,patient,and tumor-related factors significantly influence the detection threshold,diagnostic method selection,and potential results.Consequently,the implementation of LB in clinical practice still faces several challenges.The potential applications of LB range from early cancer detection to guiding targeted therapy or immunotherapy in both early and advanced cancer cases,monitoring treatment response,early identification of relapses,or assessing patient risk.On the other hand,gastric cancer(GC)is a disease often diagnosed at advanced stages.Despite recent advances in molecular understanding,the currently available treatment options have not substantially improved the prognosis for many of these patients.The application of LB in GC could be highly valuable as a non-invasive method for early diagnosis and for enhancing the management and outcomes of these patients.In this comprehensive review,from a pathologist’s perspective,we provide an overview of the main options available in LB,delve into the fundamental principles of the most studied techniques,explore the potential utility of LB application in the context of GC,and address the obstacles that need to be overcome in the future to make this innovative technique a game-changer in cancer diagnosis and treatment within clinical practice.

Finding the seed of recurrence:Hepatocellular carcinoma circulating tumor cells and their potential to drive the surgical treatment

The treatment for hepatocellular carcinoma(HCC)relies on liver resection,which is,however,burdened by a high rate of recurrence after surgery,up to 60%at 5 years.No pre-operative tools are currently available to assess the recurrence risk tailored to every single patient.Recently liquid biopsy has shown interesting results in diagnosis,prognosis and treatment allocation strategies in other types of cancers,since its ability to identify circulating tumor cells(CTCs)derived from the primary tumor.Those cells were advocated to be responsible for the majority of cases of recurrence and cancer-related deaths for HCC.In fact,after being modified by the epithelial-mesenchymal transition,CTCs circulate as“seeds”in peripheral blood,then reach the target organ as dormant cells which could be subsequently“awakened”and activated,and then initiate metastasis.Their presence may justify the disagreement registered in terms of efficacy of anatomic vs non-anatomic resections,particularly in the case of microvascular invasion,which has been recently pointed as a histological sign of the spread of those cells.Thus,their presence,also in the early stages,may justify the recurrence event also in the contest of liver transplant.Understanding the mechanism behind the tumor progression may allow improving the treatment selection according to the biological patient-based characteristics.Moreover,it may drive the development of novel biological tailored tests which could address a specific patient to neoadjuvant or adjuvant strategies,and in perspective,it could also become a new method to allocate organs for transplantation,according to the risk of relapse after liver transplant.The present paper will describe the most recent evidence on the role of CTCs in determining the relapse of HCC,highlighting their potential clinical implication as novel tumor behavior biomarkers able to influence the surgical choice.

Circulating tumor DNA for diagnosis,prognosis and treatment of gastrointestinal malignancies

Minimally invasive detection of circulating tumor DNA(ctDNA)in peripheral blood or other body fluids of patients with gastrointestinal malignancies via liquid biopsy has emerged as a promising biomarker.This is urgently needed,as conventional imaging and plasma protein-derived biomarkers lack sensitivity and specificity in prognosis,early detection of relapse or treatment monitoring.This review summarizes the potential role of liquid biopsy in diagnosis,prognosis and treatment monitoring of gastrointestinal malignancies,including upper gastrointestinal,liver,bile duct,pancreatic and colorectal cancer.CtDNA can now be part of the clinical routine as a promising,highly sensitive and specific biomarker with a broad range of applicability.Liquid-biopsy based postoperative relapse prediction could lead to improved survival by intensification of adjuvant treatment in patients identified to be at risk of early recurrence.Moreover,ctDNA allows monitoring of antineoplastic treatment success,with identification of potentially developed resistance or therapeutic targets during the course of treatment.It may also assist in early change of chemotherapy in metastatic gastrointestinal malignancies prior to imaging findings of relapse.Nevertheless,clinical utility is dependent on the tumor’s entity and burden.

Circulating tumor DNA:Where are we now?A mini review of the literature

For many years tissue biopsy has been the primary procedure to establish cancer diagnosis and determine further treatment and prognosis.However,this method has multiple drawbacks,including,to mention some,being an invasive procedure carrying significant risk for fragile patients and allowing only for a“snapshot”of the tumor biology in time.The process of liquid biopsy allows for a minimally invasive procedure that provides molecular information about underlying cancer by analyzing circulating tumor DNA(ctDNA)via next-generation sequencing technology and circulating tumor cells.This paper focuses on describing the basis of ctDNA and its current utilities.

Notes for developing a molecular test for the full characterization of circulating tumor cells

The proved association between the circulating tumor cell （CTC） levels and the patients＇ survival parameters has been growing interest to investigate the molecular profile of these neoplastic cells among which hide out precursors capable of initiating a new distant metastatic lesion. The full characterization of the tumor cells in peripheral blood of cancer patients is expected to be of help for understanding and （prospectively） for counteracting the metastatic process. The major hitch that is hampering the successful gaining of this result is the lack of a consensus onto standard operating procedures （SOPs） for performing what we generally define as the ＂liquid biopsy＂. Here we review the more recent acquisitions in the analysis of CTCs and tumor related nucleic acids, looking to the main open questions that are hampering their definitive employ in the routine clinical practice.

Applications of circulating tumor cells for prostate cancer

One of the major challenges that clinicians face is in the difficulties of accurately monitoring disease progression.Prostate cancer is among these diseases and greatly affects the health of men globally.Circulating tumor cells(CTCs)are a rare population of cancer cells that have shed from the primary tumor and entered the peripheral circulation.Not until recently,clinical applications of CTCs have been limited to using enumeration as a prognostic tool in Oncology.However,advances in emerging CTC technologies point toward new applications that could revolutionize the field of prostate cancer.It is now possible to study CTCs as components of a liquid biopsy based on morphological phenotypes,biochemical analyses,and genomic profiling.These advances allow us to gain insight into the heterogeneity and dynamics of cancer biology and to further study the mechanisms behind the evolution of therapeutic resistance.These recent developments utilizing CTCs for clinical applications will greatly impact the future of prostate cancer research and pave the way towards personalized care for men.

Cell-free circulating tumor DNA in cancer

Cancer is a common cause of death worldwide.Despite significant advances in cancer treatments,the morbidity and mortality are still enormous.Tumor heterogeneity,especially intratumoral heterogeneity,is a significant reason underlying difficulties in tumor treatment and failure of a number of current therapeutic modalities,even of molecularly targeted therapies.The development of a virtually noninvasive "liquid biopsy" from the blood has been attempted to characterize tumor heterogeneity.This review focuses on cell-free circulating tumor DNA(ctDNA) in the bloodstream as a versatile biomarker.ctDNA analysis is an evolving field with many new methods being developed and optimized to be able to successfully extract and analyze ctDNA,which has vast clinical applications.ctDNA has the potential to accurately genotype the tumor and identify personalized genetic and epigenetic alterations of the entire tumor.In addition,ctDNA has the potential to accurately monitor tumor burden and treatment response,while also being able to monitor minimal residual disease,reducing the need for harmful adjuvant chemotherapy and allowing more rapid detection of relapse.There are still many challenges that need to be overcome prior to this biomarker getting wide adoption in the clinical world,including optimization,standardization,and large multicenter trials.

Cryopreservation for delayed circulating tumor cell isolation is a valid strategy for prognostic association of circulating tumor cells in gastroesophageal cancer

AIM To demonstrate the feasibility of cryopreservation of peripheral blood mononuclear cells(PBMCs) for prognostic circulating tumor cell(CTC) detection in gastroesophageal cancer.METHODS Using 7.5 m L blood samples collected in EDTA tubes from patients with gastroesopheagal adenocarcinoma, CTCs were isolated by epithelial cell adhesion molecule based immunomagnetic capture using the Iso Flux platform. Paired specimens taken during the same blood draw(n = 15) were used to compare number of CTCs isolated from fresh and cryopreserved PBMCs. Blood samples were processed within 24 h to recover the PBMC fraction, with PBMCs used for fresh analysis immediately processed for CTC isolation. Cryopreservation of PBMCs lasted from 2 wk to 25.2 mo(median 14.6 mo). CTCs isolated from pre-treatment cryopreserved PBMCs(n = 43) were examined for associations with clinicopathological variables and survival outcomes.RESULTS While there was a significant trend to a decrease in CTC numbers associated with cryopreserved specimens(mean number of CTCs 34.4 vs 51.5, P = 0.04), this was predominately in samples with a total CTC count of > 50, with low CTC count samples less affected(P = 0.06). There was no significant association between the duration of cryopreservation and number of CTCs. In cryopreserved PBMCs from patient samples prior to treatment, a high CTC count(> 17) was associated with poorer overall survival(OS)(n = 43, HR = 4.4, 95%CI: 1.7-11.7, P = 0.0013). In multivariate analysis, after controlling for sex, age, stage, ECOG performance status, and primary tumor location, a high CTC count remained significantly associated with a poorer OS(HR = 3.7, 95%CI: 1.2-12.4, P = 0.03). CONCLUSION PBMC cryopreservation for delayed CTC isolation is a valid strategy to assist with sample collection, transporting and processing.

Circulating tumor cells in pancreatic cancer:The prognostic impact in surgical patients

Pancreatic cancer is associated with a poor prognosis,even in the early stages,mainly due to metastatic progression.New diagnostic techniques that predict unfavorable outcomes are needed in order to improve treatment strategies.Circulating tumor cells(CTCs)are showing promising results as a predictive biomarker for various tumors.In this editorial we comment on the article by Zhang et al,who published the first systematic review and meta-analysis evaluating the prognostic value of CTCs as biomarkers in early-stage pancreatic cancer patients undergoing surgery.CTCs were detected in peripheral or central venous system blood,before or during surgery.Positive CTCs showed a correlation with decreased overall survival and decreased relapse-free,disease-free and progression-free survival in this meta-analysis.However,the heterogeneity was significant.The authors suggest that this result was related to the separation methods used between studies,but other differences such as the margin status or the neoadjuvant and adjuvant treatments used are also important to consider.CTCs may be a potential prognostic biomarker in pancreatic cancer patients,but it is necessary to compare and standardize the platforms used to isolate CTCs,to compare different biomarkers from liquid biopsy and to determine the impact on prognosis when therapeutic changes are made based on CTCs levels.

Liquid Biopsy in Liquid Tumors

The availability of a minimally invasive patient simple, capable of providing tumor information, represents a valuable clinical tool. The liquid biopsy has the potential to achieve this need. Circulating cell free DNA (ccfDNA), other circulating nucleic acids such as microRNA and circulating tumor cells (CTCs), can be obtained from a peripheral blood sample. Liquid biopsy has been particularly studied in solid tumors, specially of the epitelial origin, such as a pancreatic carcinoma and advanced breast cancer. It has been considerably less applied to the study of non-solid tumors. It represents an important source for diagnosis, prognosis and predictive information. Also it is suitable to evaluate response to therapy and drugs pharmacokinetics. It provides a unique opportunity to evaluate the disease evolution in serial blood samples collection, otherwise difficult to obtain. Liquid biopsy can be rehearsed using different circulating biological fluids such as whole blood, serum, plasma and lymph, as well as, non-circulating fluids such as urine, feces, saliva, bile and accumulated pathological fluids such as ascites. This review summarizes the current status of circulating material analysis in non-solid tunors. It is specially focused on Hodgkin Lymphoma and among Non-Hodgkin Lymphoma, it refers particularly to Diffuse Large B cell Lymphoma, the most common aggressive Non-Hodgkin Lymphoma derived from germinal center B-cells in adults. It further discusses the benefit of liquid biopsy in oncohemtaological diseases and potential clinical applications.

Liquid biopsy leads to a paradigm shift in the treatment of pancreatic cancer

Pancreatic ductal adenocarcinoma(PDAC)is one of the most cancers.Its 5-year survival rate is very low.The recent induction of neoadjuvant chemotherapy and improvements in chemotherapy for patients with pancreatic cancer have resulted in improved survival outcomes.However,the prognosis of pancreatic cancer is still poor.To dramatically improve the prognosis,we need to develop more tools for early diagnosis,treatment selection,disease monitoring,and response rate evaluation.Recently,liquid biopsy(circulating free DNA,circulating tumor DNA,circulating tumor cells,exosomes,and microRNAs)has caught the attention of many researchers as a new biomarker that is minimally invasive,confers low-risk,and displays an overall state of the tumor.Thus,liquid biopsy does not employ the traditional difficulties of obtaining tumor samples from patients with advanced PDAC to investigate their molecular biological status.In addition,it allows for long-term monitoring of the molecular profile of tumor progression.These could help in identifying tumor-specific alterations that use the target structure for tailor-made therapy.Through this review,we highlighted the latest discoveries and advances in liquid biopsy technology in pancreatic cancer research and showed how it can be applied in clinical practice.

Liquid biopsy in cholangiocarcinoma:Current status and future perspectives

Cholangiocarcinoma(CCA)are a heterogeneous group of tumors in terms of aetiology,natural history,morphological subtypes,molecular alterations and management,but all sharing complex diagnosis,management,and poor prognosis.Several mutated genes and epigenetic changes have been detected in CCA,with the potential to identify diagnostic and prognostic biomarkers and therapeutic targets.Accessing tumoral components and genetic material is therefore crucial for the diagnosis,management and selection of targeted therapies;but sampling tumor tissue,when possible,is often risky and difficult to be repeated at different time points.Liquid biopsy(LB)represents a way to overcome these issues and comprises a diverse group of methodologies centering around detection of tumor biomarkers from fluid samples.Compared to the traditional tissue sampling methods LB is less invasive and can be serially repeated,allowing a real-time monitoring of the tumor genetic profile or the response to therapy.In this review,we analysis the current evidence on the possible roles of LB(circulating DNA,circulating RNA,exosomes,cytokines)in the diagnosis and management of patients affected by CCA.

The promise of liquid biopsy in cancer:a clinical perspective

The clinical utility of liquid biopsy in cancer treatment will increase as circulating tumor cells （CTCs） analysis move from the enumeration to the real-time measurement of tumor characteristics. Intratumor heterogeneity is becoming increasingly recognized as a major drawback to the shift to personalized medicine. Spatial and temporal heterogeneity might be reflected by the serial assessment of CTCs. Indeed, the developing technologies for CTCs analysis now allow digital genomic and next- generation sequencing approaches, able to differentiate molecular subtypes of the disease and to monitor genetic variation over time. The liquid biopsy of cancer might offer a real-time assessment of tumor biology, providing the opportunity to serially evaluate patients most likely to benefit from targeted drugs based on a dynamic characterization of the disease at the molecular level. Mthough hurdles remain before liquid biopsy is seen in routine clinical practice, the information derived from CTCs may facilitate the real-time identification of actionable mutations in cancer leading the way toward personalized medicine.