ALK-gene rearrangement: a comparative analysis on circulating tumour cells and tumour tissue from patients with lung adenocarcinoma

Molecular characterization of circulating tumor cells-from bench to bedside

Circulating tumor cells (CTCs) are cancer cells discovered in cancer patients' peripheral blood that successfully escape from the primary tumor site and/or metastases, struggle to survive in the bloodstream, and have potential for seeding metastases. Numerous methods have been proposed to capture CTCs. The value of CTCs as a means of understanding cancer metastasis and a major form of 'liquid biopsy' has been widely demonstrated. Recently, single-cell molecular analyses of CTCs have provided profound biological insights into tumor heterogeneity, mechanism of metastasis and tumor evolution. In addition, because CTC analysis is non-invasive, CTCs exhibit great potential as biomarkers for assessment of cancer prognosis and therapy response. In this review, we summarize modern technologies for CTC detection and isolation, single-cell genomic/transcriptomic characterization of CTCs, and prospective clinical applications of CTCs. We expect that, after further technical improvements in methods of detection and sequencing, CTC analyses will shed new light on the mechanisms driving cancer metastasis and benefit many cancer patients.

The Emerging Role of "Liquid Biopsies," Circulating Tumor Cells, and Circulating Cell-Free Tumor DNA in Lung Cancer Diagnosis and Identification of Resistance Mutations

Therapeutic advances in the treatment of lung cancer are in part due to a more complete understanding of its genomic portrait. The serial monitoring of tumor genotypes, which are instable and prone to changes under selective pressure, is becoming increasingly needed. Although tumor biopsies remain the reference standard for the diagnosis and genotyping of lung cancer, they are invasive and not always feasible. The "liquid biopsies" have the potential to overcome many of these hurdles, allowing a rapid and accurate identification of de novo and resistant genetic alterations and a real-time monitoring of treatment responses. In this review, we provide insights into new liquid diagnostic platforms and discuss the role of circulating tumor cells and circulating tumor DNA in the diagnosis and identification of resistance mutations in lung cancer.

ALK Status Assessment with Liquid Biopsies of Lung Cancer Patients

Patients with advanced stage non-small cell lung carcinoma (NSCLC) harboring an anaplastic lymphoma kinase ALK gene rearrangement, detected from a tissue sample, can benefit from targeted ALK inhibitor treatment. However, while treatment is initially effective in most cases, relapse or progression occurs due to different resistance mechanisms including mutations in the tyrosine kinase domain of echinoderm microtubule-associated protein-like 4 (EML44)-ALK. The liquid biopsy concept has recently radically changed the clinical care of NSCLC patients, in particular for those harboring an epidermal growth factor receptor (EGFR) gene mutation. Therefore, liquid biopsy is an alternative or complementary method to tissue biopsy for the detection of some resistance mutations in EGFR arising during tyrosine kinase inhibitor treatment. Moreover, in some frail patients, or if the tumor lesion is not accessible to a tissue biopsy, a liquid biopsy can also detect some activating mutations in EGFR on initial assessment. Recent studies have evaluated the possibility of also using a liquid biopsy approach to detect an ALK rearrangement and/or the emergence during inhibitor treatment of some resistance mutations in ALK. These assessments can be performed by studying circulating tumor cells by fluorescent in situ hybridization and by immunocytochemistry and/or after the isolation of RNA from plasma samples, free or associated with platelets. Thus, the liquid biopsy may be a complementary or sometimes alternative method for the assessment of the ALK status in certain NSCLC patients, as well as a non-invasive approach for early detection of ALK mutations. In this review, we highlight the current data concerning the role of the liquid biopsy for the ALK status assessment for NSCLC patients, and we compare the different approaches for this evaluation from blood samples.

Routine clinical use of circulating tumor cells for diagnosis of mutations and chromosomal rearrangements in non-small cell lung cancer-ready for prime-time?

In non-small cell lung cancer (NSCLC), diagnosis of predictive biomarkers for targeted therapies is currently done in small tumor biopsies. However, tumor biopsies can be invasive, in some cases associated with risk, and tissue adequacy, both in terms of quantity and quality is often insufficient. The development of efficient and non-invasive methods to identify genetic alterations is a key challenge which circulating tumor cells (CTCs) have the potential to be exploited for. CTCs are extremely rare and phenotypically diverse, two characteristics that impose technical challenges and impact the success of robust molecular analysis. Here we introduce the clinical needs in this disease that mainly consist of the diagnosis of epidermal growth factor receptor (EGFR) activating alterations and anaplastic lymphoma kinase (ALK) rearrangement. We present the proof-of-concept studies that explore the detection of these genetic alterations in CTCs from NSCLC patients. Finally, we discuss steps that are still required before CTCs are routinely used for diagnosis of EGFR-mutations and ALK-rearrangements in this disease.

Clinical utility of circulating tumor cells in patients with non-small-cell lung cancer

Several different studies have addressed the role of the circulating tumor cells (CTC) in non-small-cell lung cancer (NSCLC). In particular, the potential of CTC analysis in the early diagnosis of NSCLC and in the prediction of the outcome of patients with early and advanced NSCLC have been explored. A major limit of these studies is that they used different techniques for CTC isolation and enumeration, they employed different thresholds to discriminate between high- and low-risk patients, and they enrolled heterogeneous and often small cohort of patients. Nevertheless, the results of many studies are concordant in indicating a correlation between high CTC count and poor prognosis in both early and advanced NSCLC. The reduction of CTC number following treatment might also represent an important indicator of sensitivity to therapy in patients with metastatic disease. Preliminary data also suggest the potential for CTC analysis in the early diagnosis of NSCLC in high-risk individuals. However, these findings need to be confirmed in large prospective trials in order to be transferred to the clinical practice. The molecular profiling of single CTC in NSCLC might provide important information on tumor biology and on the mechanisms involved in tumor dissemination and in acquired resistance to targeted therapies. In this respect, xenografts derived from CTC might represent a valuable tool to investigate these phenomena and to develop novel therapeutic strategies.

Concordance between circulating tumor cells and clinical status during follow-up in anaplastic lymphoma kinase (ALK) non-small-cell lung cancer patients

Background

The identification of anaplastic lymphoma kinase (ALK) rearrangements is found in approximately 5% of non-small-cell lung cancers (NSCLCs). However, the development of liquid biopsies as a diagnostic tool is less developed in these cases. This study investigates the use of CTCs during treatment, together with an extended follow-up to correlate with clinical evolution.

Patients and Methods

A total of 13 patients out of a cohort of 212 patients with lung adenocarcinoma, presented ALK rearrangements (6%) confirmed by tumor biopsy. A total of 60 serial blood samples were collected from these patients who were prospectively enrolled in the study.

Results

All patients had a positive CTC count at baseline (mean = 3). The median follow-up was 9 months (range 1-17 months). Three patients underwent surgery and their CTC counts decreased after the procedure but still remained detectable. After radiotherapy, 3 cases showed an average decrease of 5 CTCs. A total of 6 patients were treated with ALK inhibitors and a partial response was observed in 3 of them, who also presented decreased CTC counts. The other 3 patients presented primary resistance, and their CTC counts were higher than those obtained prior to progression.

Conclusion

We believe that the use of CTCs for dynamic monitoring of NSCLC with ALK rearrangement and to detect disease persistence or recurrence may be a reliable technique. CTC counts may also have potential use to monitor the efficacy of ALK inhibitors, facilitating detection of resistance to treatment.

Anaplastic lymphoma kinase rearrangements in non-small-cell lung cancer: novel applications in diagnostics and treatment

The ALK gene, first identified as an anaplastic large cell lymphoma driver mutation, is dysregulated in nearly 20 different human malignancies, including 3-7% of non-small-cell lung cancers (NSCLC). In NSCLC, ALK commonly fuses with the EML4, forming a constitutively active tyrosine kinase that drives oncogenic progression. Recently, several ALK-inhibiting drugs have been developed that are more effective than standard chemotherapeutic regimens in treating advanced ALK-positive NSCLC. For this reason, molecular diagnostic testing for dysregulated ALK expression is a necessary part of identifying optimal NSCLC treatment options. Here, we review the molecular pathology of ALK-positive NSCLC, ALK molecular diagnostic techniques, ALK-targeted NSCLC treatments, and drug resistance mechanisms to ALK-targeted therapies.

Current approaches for avoiding the limitations of circulating tumor cells detection methods-implications for diagnosis and treatment of patients with solid tumors

Eight million people die of cancer each year and 90% of deaths are caused by systemic disease. Circulating tumor cells (CTCs) contribute to the formation of metastases and thus are the subject of extensive research and an abiding interest to biotechnology and pharmaceutical companies. Recent technological advances have resulted in greatly improved CTC detection, enumeration, expansion, and culture methods. However, despite the fact that nearly 150 years have passed since the first detection and description of CTCs in human blood and enormous technological progress that has taken place in this field, especially within the last decade, few CTC detection methods have been approved for routine clinical use. This reflects the substantial methodological problems related to the nature of these cells, their heterogeneity, and diverse metastatic potential. Here, we provide an overview of CTC phenotypes, including the plasticity of CTCs and the relevance of inflammation and cell fusion phenomena for CTC biology. We also review the literature on CTC detection methodology-its recent improvements, clinical significance, and efforts of its clinical application in cancer patients management. At present, CTC detection remains a challenging diagnostic approach as a result of numerous current methodological limitations. This is especially problematic during the early stages of the disease due to the small numbers of CTCs released into the blood of cancer patients. Nonetheless, the rapid development of novel techniques of CTC detection and enumeration in peripheral blood is expected to expedite their implementation in the clinical setting. It is of utmost importance to understand the biology of CTCs and their distinct populations as a prerequisite for achieving this ultimate goal.

Circulating Tumor Cells with Aberrant ALK Copy Number Predict Progression-Free Survival during Crizotinib Treatment in ALK-Rearranged Non-Small Cell Lung Cancer Patients

The duration and magnitude of clinical response are unpredictable in ALK-rearranged non-small cell lung cancer (NSCLC) patients treated with crizotinib, although all patients invariably develop resistance. Here, we evaluated whether circulating tumor cells (CTC) with aberrant ALK-FISH patterns [ALK-rearrangement, ALK-copy number gain (ALK-CNG)] monitored on crizotinib could predict progression-free survival (PFS) in a cohort of ALK-rearranged patients. Thirty-nine ALK-rearranged NSCLC patients treated with crizotinib as first ALK inhibitor were recruited prospectively. Blood samples were collected at baseline and at an early time-point (2 months) on crizotinib. Aberrant ALK-FISH patterns were examined in CTCs using immunofluorescence staining combined with filter-adapted FISH after filtration enrichment. CTCs were classified into distinct subsets according to the presence of ALK-rearrangement and/or ALK-CNG signals. No significant association between baseline numbers of ALK-rearranged or ALK-CNG CTCs and PFS was observed. However, we observed a significant association between the decrease in CTC number with ALK-CNG on crizotinib and a longer PFS (likelihood ratio test, P = 0.025). In multivariate analysis, the dynamic change of CTC with ALK-CNG was the strongest factor associated with PFS (HR, 4.485; 95% confidence interval, 1.543-13.030, P = 0.006). Although not dominant, ALK-CNG has been reported to be one of the mechanisms of acquired resistance to crizotinib in tumor biopsies. Our results suggest that the dynamic change in the numbers of CTCs with ALK-CNG may be a predictive biomarker for crizotinib efficacy in ALK-rearranged NSCLC patients. Serial molecular analysis of CTC shows promise for real-time patient monitoring and clinical outcome prediction in this population. Cancer Res; 77(9); 2222-30. ©2017 AACR.

Molecular biomarkers for lung adenocarcinoma

The identification of oncogenic driver alterations that underlie sensitivity to small inhibitors has led to growing interest in identifying additional targetable oncogenes in nonsmall cell lung cancer. Although the therapeutic impact of the discovery of these alterations has now been widely demonstrated, the epidemiological data associated with each of these biomarkers remain insufficiently studied. In this review, we discuss the techniques used to discover each of these candidate oncogenes, their prevalence in nonsmall cell lung cancer, and briefly outline the epidemiological features of the major oncogenes and ways in which their identification can determine therapeutic strategies.

Clinical Applications of Circulating Tumor Cells in Pharmacotherapy: Challenges and Perspectives

Screening for circulating tumor cells (CTCs) has been identified as one approach to ultrasensitive liquid biopsy in real-time monitoring of cancer patients. The detection of CTCs in peripheral blood from cancer patients is promising as a diagnostic tool; however, the application of CTCs in therapeutic treatment still faces serious challenges with respect to specificity and sensitivity. Here, we review the significant roles of CTCs in metastasis and the strengths and weaknesses of the currently available methods for CTC detection and characterization. Moreover, we discuss the clinical application of CTCs as markers for patient prognosis, and we specifically focus on the application of CTCs as indicators in cancer pharmacotherapy. Characterization of the detected CTCs will provide new biologic perspectives and clinical applications for the treatment of cancer patients with metastasis.

The liquid biopsy in lung cancer

The incidence of lung cancer has significantly increased over the last century, largely due to smoking, and remains the most common cause of cancer deaths worldwide. This is often due to lung cancer first presenting at late stages and a lack of curative therapeutic options at these later stages. Delayed diagnoses, inadequate tumor sampling, and lung cancer misdiagnoses are also not uncommon due to the limitations of the tissue biopsy. Our better understanding of the tumor microenvironment and the systemic actions of tumors, combined with the recent advent of the liquid biopsy, may allow molecular diagnostics to be done on circulating tumor markers, particularly circulating tumor DNA. Multiple liquid biopsy molecular methods are presently being examined to determine their efficacy as surrogates to the tumor tissue biopsy. This review will focus on new liquid biopsy technologies and how they may assist in lung cancer detection, diagnosis, and treatment.

Technical Insights into Highly Sensitive Isolation and Molecular Characterization of Fixed and Live Circulating Tumor Cells for Early Detection of Tumor Invasion

Circulating Tumor Cells (CTC) and Circulating Tumor Microemboli (CTM) are Circulating Rare Cells (CRC) which herald tumor invasion and are expected to provide an opportunity to improve the management of cancer patients. An unsolved technical issue in the CTC field is how to obtain highly sensitive and unbiased collection of these fragile and heterogeneous cells, in both live and fixed form, for their molecular study when they are extremely rare, particularly at the beginning of the invasion process. We report on a new protocol to enrich from blood live CTC using ISET^® (Isolation by SizE of Tumor/Trophoblastic Cells), an open system originally developed for marker-independent isolation of fixed tumor cells. We have assessed the impact of our new enrichment method on live tumor cells antigen expression, cytoskeleton structure, cell viability and ability to expand in culture. We have also explored the ISET^®in vitro performance to collect intact fixed and live cancer cells by using spiking analyses with extremely low number of fluorescent cultured cells. We describe results consistently showing the feasibility of isolating fixed and live tumor cells with a Lower Limit of Detection (LLOD) of one cancer cell per 10 mL of blood and a sensitivity at LLOD ranging from 83 to 100%. This very high sensitivity threshold can be maintained when plasma is collected before tumor cells isolation. Finally, we have performed a comparative next generation sequencing (NGS) analysis of tumor cells before and after isolation from blood and culture. We established the feasibility of NGS analysis of single live and fixed tumor cells enriched from blood by our system. This study provides new protocols for detection and characterization of CTC collected from blood at the very early steps of tumor invasion.

Strategies for Isolation and Molecular Profiling of Circulating Tumor Cells

Cancer is the leading cause of death by disease worldwide, and metastasis is responsible for more than 90% of the mortality of cancer patients. Metastasis occurs when tumor cells leave the primary tumor, travel through the blood stream as circulating tumor cells (CTCs), and then colonize secondary tumors at sites distant from the primary tumor. The capture, identification, and analysis of CTCs offer both scientific and clinical benefits. On the scientific side, the analysis of CTCs could help elucidate possible genetic alterations and signaling pathway aberrations during cancer progression, which could then be used to find new methods to stop cancer progression. On the clinical side, non-invasive testing of a patient's blood for CTCs can be used for patient diagnosis and prognosis, as well as subsequent monitoring of treatment efficacy in routine clinical practice. Additionally, investigation of CTCs early in the progression of cancer may reveal targets for initial cancer detection and for anti-cancer treatment. This chapter will evaluate strategies and devices used for the isolation and identification of CTCs directly from clinical samples of blood. Recent progress in the understanding of the significance of both single CTCs and circulating tumor microemboli will be discussed. Also, advancements in the use of CTC-based liquid biopsy in clinical diagnosis and the potential of CTC-based molecular characterization for use in clinical applications will be summarized.

Strategies to design clinical studies to identify predictive biomarkers in cancer research

The discovery of reliable biomarkers to predict efficacy and toxicity of anticancer drugs remains one of the key challenges in cancer research. Despite its relevance, no efficient study designs to identify promising candidate biomarkers have been established. This has led to the proliferation of a myriad of exploratory studies using dissimilar strategies, most of which fail to identify any promising targets and are seldom validated. The lack of a proper methodology also determines that many anti-cancer drugs are developed below their potential, due to failure to identify predictive biomarkers. While some drugs will be systematically administered to many patients who will not benefit from them, leading to unnecessary toxicities and costs, others will never reach registration due to our inability to identify the specific patient population in which they are active. Despite these drawbacks, a limited number of outstanding predictive biomarkers have been successfully identified and validated, and have changed the standard practice of oncology. In this manuscript, a multidisciplinary panel reviews how those key biomarkers were identified and, based on those experiences, proposes a methodological framework-the DESIGN guidelines-to standardize the clinical design of biomarker identification studies and to develop future research in this pivotal field.

Liquid Biopsy in Non-Small Cell Lung Cancer

Liquid biopsy analyses are already incorporated in the routine clinical practice in many hospitals and oncology departments worldwide, improving the selection of treatments and monitoring of lung cancer patients. Although they have not yet reached its full potential, liquid biopsy-based tests will soon be as widespread as “standard” biopsies and imaging techniques, offering invaluable diagnostic, prognostic, and predictive information. This review summarizes the techniques available for the isolation and analysis of circulating free DNA and RNA, exosomes, tumor-educated platelets, and circulating tumor cells from the blood of cancer patients, presents the methodological challenges associated with each of these materials, and discusses the clinical applications of liquid biopsy testing in lung cancer.

Is it feasible to detect epidermal growth factor receptor mutations in circulating tumor cells in nonsmall cell lung cancer?: A meta-analysis

BACKGROUND

The value of circulating tumor cells (CTCs) in detecting epidermal growth factor receptor (EGFR) mutations in patients with nonsmall cell lung cancer (NSCLC) is controversial. We performed a meta-analysis to investigate the diagnostic significance of CTCs with tumor tissues as the standard control.

METHODS

A systematic literature search, including papers published until November 26, 2015, was performed using PubMed, Medline, Embase, Web of Science, and the China National Knowledge Infrastructure, and the references of retrieved articles were screened. The pooled sensitivity, specificity, and diagnostic odds ratio (DOR) were calculated according to the data selection from the included studies. The evaluation indexes of the diagnostic performance were the summary receiver operating characteristic curve (SROC) and area under the SROC (AUSROC).

RESULTS

Eight eligible articles with a total of 170 participants were identified in our meta-analysis. The pooled sensitivity and specificity were 0.91 [95% CI: 0.55-0.99] and 0.99 [95% CI: 0.59-1.00]. The positive likelihood ratio and negative likelihood ratio were 68 [95% CI: 1.4-3364] and 0.09 [95% CI: 0.01-0.64], respectively. The DOR was 788 [95% CI: 9-71884]. The high diagnostic performance of CTCs in detecting EGFR mutations was indicated by the AUSROC of 0.99 [95% CI: 0.98-1.00].

CONCLUSIONS

CTCs are a feasible and highly specific biomarker for detecting the EGFR mutation status in NSCLC patients.

Personalized treatment in advanced ALK-positive non-small cell lung cancer: from bench to clinical practice

The discovery of anaplastic lymphoma kinase (ALK) gene rearrangements and the development of tyrosine kinase inhibitors (TKI) that target them have achieved unprecedented success in the management of patients with ALK-positive non-small cell lung cancer (NSCLC). Despite the high efficacy of crizotinib, the first oral ALK TKI approved for the treatment of ALK-positive NSCLC, almost all patients inevitably develop acquired resistance, showing disease progression in the brain or in other parenchymal sites. Second- or third-generation ALK TKIs have shown to be active in crizotinib-pretreated or crizotinib-naïve ALK-positive patients, even in those with brain metastases. In this review, the current knowledge regarding ALK-positive NSCLC, focusing on the biology of the disease and the available therapeutic options are discussed.

Fusion gene and splice variant analyses in liquid biopsies of lung cancer patients

Obtaining a biopsy of solid tumors requires invasive procedures that strongly limit patient compliance. In contrast, a blood extraction is safe, can be performed at many time points during the course disease and encourages appropriate therapy modifications, potentially improving the patient's clinical outcome and quality of life. Fusion of the tyrosine kinase genes anaplastic lymphoma kinase (ALK), C-ROS oncogen 1 (ROS 1), rearranged during transfection (RET) and neurotrophic tyrosine kinase 1 (NTRK1) occur in 1-5% of lung adenocarcinomas and constitute therapeutic targets for tyrosine kinase inhibitors. In addition, a MET splicing variant of exon 14, has been reported in 2-4% of lung adenocarcinoma and recent studies suggests that targeted therapies inhibiting MET signaling would be beneficial for patients with this alteration. In this review, we will summarize the new techniques recently developed to detect ALK, RET, ROS and NTRK1 fusions and MET exon 14 splicing variant in liquid biopsy using plasma, serum, circulating tumor cells (CTCs), platelets and exosomes as starting material.

Circulating tumor cells versus circulating tumor DNA in lung cancer-which one will win?

Liquid biopsies appear to be a reliable alternative to conventional biopsies that can provide both precise molecular data useful for improving the clinical management of lung cancer patients as well as a less invasive way of monitoring tumor behavior. These advances are supported by important biotechnological developments in the fields of circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA). Analysis of CTCs and ctDNA may be useful in treatment selection, for response monitoring, and in studying resistance mechanisms. This review focuses on the most recent technological achievements and the most relevant clinical applications for lung cancer patients in the CTC and ctDNA fields, highlighting those that are already (or are close to) being implemented in daily clinical practice.

Circulating Tumor Cell and Cell-free Circulating Tumor DNA in Lung Cancer

Circulating tumor cells (CTCs) are tumor cells that are separated from the primary site or metastatic lesion and disseminate in blood circulation. CTCs are considered to be part of the long process of cancer metastasis. As a 'liquid biopsy', CTC molecular examination and investigation of single cancer cells create an important opportunity for providing an understanding of cancer biology and the process of metastasis. In the last decade, we have seen dramatic development in defining the role of CTCs in lung cancer in terms of diagnosis, genomic alteration determination, treatment response and, finally, prognosis prediction. The aims of this review are to understand the basic biology and to review methods of detection of CTCs that apply to the various types of solid tumor. Furthermore, we explored clinical applications, including treatment monitoring to anticipate therapy resistance as well as biomarker analysis, in the context of lung cancer. We also explored the potential use of cell-free circulating tumor DNA (ctDNA) in the genomic alteration analysis of lung cancer.

Pathologists and liquid biopsies: to be or not to be?

Recently, the advent of therapies targeting genomic alterations has improved the care of patients with certain types of cancer. While molecular targets were initially detected in nucleic acid samples extracted from tumor tissue, detection of nucleic acids in circulating blood has allowed the development of what has become known as liquid biopsies, which provide a complementary and alternative sample source allowing identification of genomic alterations that might be addressed by targeted therapy. Consequently, liquid biopsies might rapidly revolutionize oncology practice in allowing administration of more effective treatments. Liquid biopsies also provide an approach towards short-term monitoring of metastatic cancer patients to evaluate efficacy of treatment and/or early detection of secondary mutations responsible for resistance to treatment. In this context, pathologists, who have already been required in recent years to take interest in the domain of molecular pathology of cancer, now face new challenges. The attitude of pathologists to and level of involvement in the practice of liquid biopsies, including mastering the methods employed in molecular analysis of blood samples, need close attention. Regardless of the level of involvement of pathologists in this new field, it is mandatory that oncologists, biologists, geneticists, and pathologists work together to coordinate the pre-analytical, analytical, and post-analytical phases of molecular assessment of tissue and liquid samples of individual cancer patients. The challenges include (1) implementation of effective and efficient procedures for reception and analysis of liquid and tissue samples for histopathological and molecular evaluation and (2) assuring short turn-around times to facilitate rapid optimization of individual patient treatment. In this paper, we will review the following: (1) recent data concerning the concept of liquid biopsies in oncology and its development for patient care, (2) advantages and limitations of molecular analyses performed on blood samples compared to those performed on tissue samples, and (3) short-term challenges facing pathologists in dealing with liquid biopsies of cancer patients and new strategies to early detect metastatic tumor cell clones.

Evaluation and consequences of heterogeneity in the circulating tumor cell compartment

A growing understanding of the molecular biology of cancer and the identification of specific aberrations driving cancer evolution have led to the development of various targeted agents. Therapeutic decisions concerning these drugs are often guided by single biopsies of the primary tumor. Yet, it is well known that tumors can exhibit significant heterogeneity and change over time as a result of selective pressure. Circulating tumor cells (CTCs) are shed from various tumor sites and are thought to represent the molecular landscape of a patient's overall tumor burden. Moreover, a minimal-invasive liquid biopsy facilitates monitoring of clonal evolution during therapy pressure and disease progression in real-time. While more information becomes available regarding heterogeneity among CTCs, comparison between these studies is needed. In this review, we focus on the genomic and transcriptional heterogeneity found in the CTC compartment, and its significance for clinical decision making.

Non-Invasive Methods to Monitor Mechanisms of Resistance to Tyrosine Kinase Inhibitors in Non-Small-Cell Lung Cancer: Where Do We Stand?

The induction of resistance mechanisms represents an important problem for the targeted therapy of patients with non-small-cell lung cancer (NSCLC). The best-known resistance mechanism induced during treatment with epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) is EGFR T790M mutation for which specific drugs are have been developed. However, other molecular alterations have also been reported as induced resistance mechanisms to EGFR-TKIs. Similarly, there is growing evidence of acquired resistance mechanisms to anaplastic lymphoma kinase (ALK)-TKI treatment. A better understanding of these acquired resistance mechanisms is essential in clinical practice as patients could be treated with specific drugs that are active against the induced alterations. The use of free circulating tumor nucleic acids or circulating tumor cells (CTCs) enables resistance mechanisms to be characterized in a non-invasive manner and reduces the need for tumor re-biopsy. This review discusses the main resistance mechanisms to TKIs and provides a comprehensive overview of innovative strategies to evaluate known resistance mechanisms in free circulating nucleic acids or CTCs and potential future orientations for these non-invasive approaches.

Monitoring KRAS mutations in circulating DNA and tumor cells using digital droplet PCR during treatment of KRAS-mutated lung adenocarcinoma

Liquid biopsies are a new non-invasive strategy to detect and monitor the biology of non-small-cell lung cancer (NSCLC) in the era of personalized medicine. KRAS is an oncogenic driver that is mutated in 30% of NSCLCs and is associated with a poor prognosis. 62 samples from 32 patients, treated for metastatic KRAS-mutated lung adenocarcinoma, had DNA extracted from plasma and circulating tumor cells (CTCs) prospectively tested for the presence of KRAS mutations using droplet digital PCR. A KRAS mutation was detected in 82% of patients. Sensitivity was 78% for circulating free DNA (cfDNA) and 34% for CTCs. The presence of a KRAS mutation in cfDNA was correlated with a poor response to chemotherapy or targeted therapy. When a KRAS-mutated-DNA was detected and then monitored in cfDNA, its variation during targeted or conventional therapy was correlated with response, according to RECIST criteria, in 87.5% of cases (n=14/16), whereas this correlation was observed in 37.5% of cases for CTCs (n=3/8). We report the usefulness of using digital droplet PCR on liquid biopsies to predict and monitor responses to treatment of KRAS-mutated lung adenocarcinoma. ctDNA was much more sensitive than CTCs in this context.

Method for semi-automated microscopy of filtration-enriched circulating tumor cells

BACKGROUND

Circulating tumor cell (CTC)-filtration methods capture high numbers of CTCs in non-small-cell lung cancer (NSCLC) and metastatic prostate cancer (mPCa) patients, and hold promise as a non-invasive technique for treatment selection and disease monitoring. However filters have drawbacks that make the automation of microscopy challenging. We report the semi-automated microscopy method we developed to analyze filtration-enriched CTCs from NSCLC and mPCa patients.

METHODS

Spiked cell lines in normal blood and CTCs were enriched by ISET (isolation by size of epithelial tumor cells). Fluorescent staining was carried out using epithelial (pan-cytokeratins, EpCAM), mesenchymal (vimentin, N-cadherin), leukocyte (CD45) markers and DAPI. Cytomorphological staining was carried out with Mayer-Hemalun or Diff-Quik. ALK-, ROS1-, ERG-rearrangement were detected by filter-adapted-FISH (FA-FISH). Microscopy was carried out using an Ariol scanner.

RESULTS

Two combined assays were developed. The first assay sequentially combined four-color fluorescent staining, scanning, automated selection of CD45(-) cells, cytomorphological staining, then scanning and analysis of CD45(-) cell phenotypical and cytomorphological characteristics. CD45(-) cell selection was based on DAPI and CD45 intensity, and a nuclear area >55 μm(2). The second assay sequentially combined fluorescent staining, automated selection of CD45(-) cells, FISH scanning on CD45(-) cells, then analysis of CD45(-) cell FISH signals. Specific scanning parameters were developed to deal with the uneven surface of filters and CTC characteristics. Thirty z-stacks spaced 0.6 μm apart were defined as the optimal setting, scanning 82 %, 91 %, and 95 % of CTCs in ALK-, ROS1-, and ERG-rearranged patients respectively. A multi-exposure protocol consisting of three separate exposure times for green and red fluorochromes was optimized to analyze the intensity, size and thickness of FISH signals.

CONCLUSIONS

The semi-automated microscopy method reported here increases the feasibility and reliability of filtration-enriched CTC assays and can help progress towards their validation and translation to the clinic.

Clinical Utility of Liquid Diagnostic Platforms in Non-Small Cell Lung Cancer

: A firmer understanding of the genomic landscape of lung cancer has recently led to targeted, therapeutic advances in non-small cell lung cancer. Historically, the reference standard for the diagnosis and genetic interrogation for advanced-stage patients has been tissue acquisition via computed tomography-guided core or fine needle aspiration biopsy. However, this process can frequently put the patient at risk and remains complicated by sample availability and tumor heterogeneity. In addition, the time required to complete the diagnostic assays can negatively affect clinical care. Technological advances in recent years have led to the development of blood-based diagnostics or "liquid biopsies" with great potential to quickly diagnose and genotype lung cancer using a minimally invasive technique. Recent studies have suggested that molecular alterations identified in cell-free DNA (cfDNA) or circulating tumor DNA can serve as an accurate molecular proxy of tumor biology and reliably predict the response to tyrosine kinase therapy. In addition, several trials have demonstrated the high accuracy of microRNA (miRNA) platforms in discerning cancerous versus benign nodules in high-risk, screened patients. Despite the promise of these platforms, issues remain, including varying sensitivities and specificities between competing platforms and a lack of standardization of techniques and downstream processing. In the present report, the clinical applications of liquid biopsy technologies, including circulating tumor cells, proteomics, miRNA, and cfDNA for NSCLC, are reviewed and insight is provided into the diagnostic and therapeutic implications and challenges of these platforms.

IMPLICATIONS FOR PRACTICE

Although tumor biopsies remain the reference standard for the diagnosis and genotyping of non-small cell lung cancer, they remain fraught with logistical complexities that can delay treatment decisions and affect clinical care. Liquid diagnostic platforms, including cell-free DNA, proteomic signatures, RNA (mRNA and microRNA), and circulating tumor cells, have the potential to overcome many of these barriers, including rapid and accurate identification of de novo and resistant genetic alterations, real-time monitoring of treatment responses, prognosis of outcomes, and identification of minimal residual disease. The present report provides insights into new liquid diagnostic platforms in non-small cell lung cancer and discusses the promise and challenges of their current and future clinical use.

The prognostic role of circulating tumor cells in lung cancer

INTRODUCTION

Circulating tumor cells (CTCs) can be isolated from the peripheral blood of cancer patients. Several studies to assess the prognostic and/or predictive role of CTCs have been performed in lung cancer patients.

AREAS COVERED

The state-of-the-art of the role of CTCs in lung cancer patients is reviewed and discussed. A structured search of bibliographic databases for peer-reviewed research literature and of main meetings using a focused review question was undertaken. Expert commentary: Although in the revised studies different technologies, cutoffs, patients' populations and statistical approaches have been used, a high CTCs count as prognostic role in small-cell lung cancer is suggested, whereas additional studies are required to confirm this correlation in non-small-cell lung cancer. A reduction in CTCs count is also likely to be correlated with the lung cancer patients' outcome. Large prospective trials need to confirm the prognostic and/or predictive role of CTCs in lung cancer.

Circulating Biomarkers in Non-Small-Cell Lung Cancer: Current Status and Future Challenges

Despite recent advances, non-small-cell lung cancer remains a devastating disease and carries a grim prognosis. Major contributing factors include difficulties in diagnosing the disease early in its course during the asymptomatic stage and the poor understanding of the biology underlying disease progression. Liquid biopsies, noninvasive blood tests that detect circulating biomarkers such as circulating tumor cells and tumor-derived nucleic acid fragments, are in a rapidly evolving field of research that could provide answers to both of these unmet needs. Herein, we review the relevant data concerning the diagnostic, predictive, and prognostic significance of 3 distinct but potentially complementary circulating biomarkers in non-small-cell lung cancer: circulating tumor cells, cell-free DNA, and microRNAs.

High expression of TRF2, SOX10, and CD10 in circulating tumor microemboli detected in metastatic melanoma patients. A potential impact for the assessment of disease aggressiveness

Circulating tumors cells (CTCs) can be detected in the blood of metastatic melanoma patients (MMPs) both as isolated circulating tumor cells (iCTCs) and circulating tumor microemboli (CTMs), but their clinical significance remains unknown. The aim of this work was to evaluate the prognostic impact in metastatic cutaneous melanoma of CTMs and iCTCs identified by a cytomorphological approach using the isolation by size of tumor cell (ISET) method. We characterized the phenotype of CTCs using anti-PS100, anti-SOX10, anti-CD10, and anti-TRF2 antibodies. 128 MMPs and 37 control healthy individuals with benign nevi were included in this study. Results were compared to the follow-up of patients. 109/128 (85%) MMPs showed CTCs, 44/128 (34%) with 2 to 6 CTMs and 65/128 (51%) with 4 to 9 iCTCs. PS100 expression was homogeneous in iCTCs and heterogeneous in CTMs. SOX10, CD10, and TRF2 were mainly expressed in CTMs. None of the control subjects demonstrated circulating malignant tumor cells. Overall survival was significantly decreased in patients with CTMs, independently of the therapeutic strategies. In conclusion, the presence of CTMs is an independent predictor of shorter survival from the time of diagnosis of MMPs.

Possible applications of circulating tumor cells in patients with non small cell lung cancer

Recent experiences indicate that, as already reported for other types of cancer, circulating tumor cells (CTCs) may play a role also in non small cell lung cancer (NSCLC) for diagnosis, therapy monitoring and prognostic purposes. CTCs evaluation could be particularly relevant in this clinical setting not only for the objective difficulty in obtaining tumor tissue, but also because of the lack of reliable tumor markers. In the current review, we will focus on the possible applications of CTCs in NSCLC patients.

Liquid Biopsy in Lung Cancer: A Perspective From Members of the Pulmonary Pathology Society

Liquid biopsy has received extensive media coverage and has been called the holy grail of cancer detection. Attempts at circulating tumor cell and genetic material capture have been progressing for several years, and recent financially and technically feasible improvements of cell capture devices, plasma isolation techniques, and highly sensitive polymerase chain reaction- and sequencing-based methods have advanced the possibility of liquid biopsy of solid tumors. Although practical use of circulating RNA-based testing has been hindered by the need to fractionate blood to enrich for RNAs, the detection of circulating tumor cells has profited from advances in cell capture technology. In fact, the US Food and Drug Administration has approved one circulating tumor cell selection platform, the CellSearch System. Although the use of liquid biopsy in a patient population with a genomically defined solid tumor may potentially be clinically useful, it currently does not supersede conventional pretreatment tissue diagnosis of lung cancer. Liquid biopsy has not been validated for lung cancer diagnosis, and its lower sensitivity could lead to significant diagnostic delay if liquid biopsy were to be used in lieu of tissue biopsy. Ultimately, notwithstanding the enthusiasm encompassing liquid biopsy, its clinical utility remains unproven.

Using CTCs for pharmacogenomic analysis

In the era of precision medicine in oncology, pharmacogenomic assessment is a vital step in delivering personalized care. Increasing evidence points towards the importance of assessing molecular features of the advanced disease, rather than relying on the primary tumor sample, in order to appreciate the evolution of the tumor and to target relevant features. Circulating tumor cells (CTCs) represent a novel method of tumor sampling, as they offer a contemporaneous picture of the current disease state without the need for invasive needle biopsy. As they may derive from any number of metastatic sites, the potential to capture the heterogeneity of the disease is increased. Improvements in CTC capture, enrichment and isolation technology now allow sophisticated interrogation of these cells, such that pharmacogenomic assessment of CTCs is now possible, and the clinical potential is being explored. We review current and potential uses for CTCs for pharmacogenomic analysis.

Isolation and Characterization of Circulating Tumor Cells in Squamous Cell Carcinoma of the Lung Using a Non-EpCAM-Based Capture Method

INTRODUCTION

The exclusion of circulating tumor cells (CTCs) that have lost epithelial antigens during the epithelial-to-mesenchymal transition (EMT) process by using Epithelial Cell Adhesion Molecule (EpCAM) based capture methods is still a matter of debate. In this study, cells obtained after depletion procedure from blood samples of squamous cell lung cancer (SQCLC) patients were identified based on morphology and characterized with the combination of FISH assessment and immunophenotypic profile.

MATERIALS AND METHODS

Five mL blood samples, collected from 55 advanced SQCLC patients, were analyzed by a non-EpCAM-based capture method. After depletion of leukocytes and erythroid cells, the negative fraction was characterized by both FISH using a fibroblast growth factor receptor 1 (FGFR1) probe and by immunocytochemistry. Thirty healthy donors were also tested.

RESULTS

Based on morphology (nuclear dimension ≥10 μm, shape and hypercromatic aspect) suspicious circulating cells clearly distinguishable from contaminant leukocytes were observed in 49/55 (89%) SQCLC patients. Thirty-four of the 44 (77%) samples evaluable for FGFR1 FISH showed ≥ 6 FGFR1 gene copy number on average per cell. Vimentin expression involved 43% (18/42) of pooled circulating SQCLC cells, whereas only 29% (14/48) were EpCAM positive. Confocal microscopy confirmed the localization of FGFR1 probe in suspicious circulating cells. Suspicious circulating elements were also observed in healthy donors and did not show any epithelial associated antigens. A significantly lower number of suspicious circulating cells in healthy donors compared to SQCLC patients was found.

CONCLUSIONS

Among the heterogeneous cell population isolated by depletion procedure, the coexistence of cells with epithelial and/or mesenchymal phenotype suggests that EMT may participate to transendothelial invasion and migration of tumor cells in advanced SQCLC. The finding of cells with neither EpCAM or EMT phenotype, retrieved after non-EpCAM-based systems, underlines the presence of suspicious elements in the blood of both SQCLC patients and healthy donors. Further phenotyping and molecular analyses are necessary to fully characterize these circulating elements.

The potential diagnostic power of circulating tumor cell analysis for non-small-cell lung cancer

In non-small-cell lung cancer (NSCLC), genotyping tumor biopsies for targetable somatic alterations has become routine practice. However, serial biopsies have limitations: they may be technically difficult or impossible and could incur serious risks to patients. Circulating tumor cells (CTCs) offer an alternative source for tumor analysis that is easily accessible and presents the potential to identify predictive biomarkers to tailor therapies on a personalized basis. Examined here is our current knowledge of CTC detection and characterization in NSCLC and their potential role in EGFR-mutant, ALK-rearranged and ROS1-rearranged patients. This is followed by discussion of the ongoing issues such as the question of CTC partnership as diagnostic tools in NSCLC.

Circulating tumor cell isolation: the assets of filtration methods with polycarbonate track-etched filters

Circulating tumor cells (CTCs) arise from primary or secondary tumors and enter the bloodstream by active or passive intravasation. Given the low number of CTCs, enrichment is necessary for detection. Filtration methods are based on selection of CTCs by size using a filter with 6.5 to 8 µm pores. After coloration, collected CTCs are evaluated according to morphological criteria. Immunophenotyping and fluorescence in situ hybridization techniques may be used. Selected CTCs can also be cultivated in vitro to provide more material. Analysis of genomic mutations is difficult because it requires adapted techniques due to limited DNA materials. Filtration-selected CTCs have shown prognostic value in many studies but multicentric validating trials are mandatory to strengthen this assessment. Other clinical applications are promising such as follow-up, therapy response prediction and diagnosis. Microfluidic emerging systems could optimize filtration-selected CTCs by increasing selection accuracy.

Detection of Circulating Tumor Cells in Non-Small Cell Lung Cancer

Lung cancer is the most common cause of cancer-related deaths that frequently metastasizes prior to disease diagnosis. Circulating tumor cells (CTCs) are found in many different types of epithelial tumors and are of great clinical interest in terms of prognosis and therapy intervention. Here, we present and discuss epithelial cell adhesion molecule-dependent and -independent capture of CTCs in non-small cell lung cancer (NSCLC) and the clinical relevance of CTC detection and characterization. Taking blood samples and analyzing CTCs as "liquid biopsy" might be a far less invasive diagnostic strategy than biopsies of lung tumors or metastases. Moreover, sequential blood sampling allows to study the dynamic changes of tumor cells during therapy, in particular the development of resistant tumor cell clones.

Non-invasive approaches to monitor EGFR-TKI treatment in non-small-cell lung cancer

Tyrosine kinase inhibitors of epidermal growth factor receptor (EGFR-TKIs) are standard treatments for advanced non-small-cell lung cancer (NSCLC) patients harboring activating epidermal growth factor receptor (EGFR) mutations. Nowadays, tumor tissues acquired by surgery or biopsy are the routine materials for EGFR mutation analysis. However, the accessibility of tumor tissues is not always satisfactory in advanced NSCLC. Moreover, a high proportion of NSCLC patients will eventually develop resistance to EGFR-TKIs. Invasive procedures, such as surgery or biopsy, are impractical to be performed repeatedly to assess the evolution of EGFR-TKI resistance. Thus, exploring some convenient and less invasive techniques to monitor EGFR-TKI treatment is urgently needed. Circulating cell-free tumor DNA (ctDNA) has a high degree of specificity to detect EGFR mutations in NSCLC. Besides, ctDNA is capable of monitoring the disease progression during EGFR-TKI treatment. Certain serum microRNAs that correlate with EGFR signaling pathway, such as miR-21 and miR-10b, have been demonstrated to be helpful in evaluating the efficiency of EGFR-TKI therapeutics. A commercialized serum-based proteomic test, named VeriStrat test, has shown an outstanding ability to predict the clinical outcome of NSCLC patients receiving EGFR-TKIs. Analysis of EGFR mutations in circulating tumor cells (CTCs) is feasible, and CTCs represent a promising material to predict EGFR-TKI-treatment efficacy and resistance. These evidences suggested that non-invasive techniques based on serum or plasma samples had a great potential for monitoring EGFR-TKI treatment in NSCLC. In this review, we summarized these non-invasive approaches and considered their possible applications in EGFR-TKI-treatment monitoring.

Using circulating tumor cells to inform on prostate cancer biology and clinical utility

Substantial advances in the molecular biology of prostate cancer have led to the approval of multiple new systemic agents to treat men with metastatic castration-resistant prostate cancer (mCRPC). These treatments encompass androgen receptor directed therapies, immunotherapies, bone targeting radiopharmaceuticals and cytotoxic chemotherapies. There is, however, great heterogeneity in the degree of patient benefit with these agents, thus fueling the need to develop predictive biomarkers that are able to rationally guide therapy. Circulating tumor cells (CTCs) have the potential to provide an assessment of tumor-specific biomarkers through a non-invasive, repeatable "liquid biopsy" of a patient's cancer at a given point in time. CTCs have been extensively studied in men with mCRPC, where CTC enumeration using the Cellsearch® method has been validated and FDA approved to be used in conjunction with other clinical parameters as a prognostic biomarker in metastatic prostate cancer. In addition to enumeration, more sophisticated molecular profiling of CTCs is now feasible and may provide more clinical utility as it may reflect tumor evolution within an individual particularly under the pressure of systemic therapies. Here, we review technologies used to detect and characterize CTCs, and the potential biological and clinical utility of CTC molecular profiling in men with metastatic prostate cancer.