Sputum Cell-Free DNA: Valued Surrogate Sample for Detection of EGFR Mutation in Patients with Advanced Lung Adenocarcinoma

Liquid biopsy: Comprehensive overview of circulating tumor DNA (Review)

Traditional tumor diagnosis methods rely on tissue biopsy, which can be invasive and unsuitable for long-term monitoring of tumor dynamics. The advent of liquid biopsy has notably improved the overall management of patients with cancer. Liquid biopsy techniques primarily involve detection of circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA). The present review focuses on ctDNA because of its significance in tumor diagnosis, monitoring and treatment. The use of ctDNA-based liquid biopsy offers several advantages, including non-invasive or minimally invasive collection methods, the ability to conduct repeated assessment and comprehensive insights into tumor biology. It serves crucial roles in disease management by facilitating screening of high-risk patients, dynamically monitoring therapeutic responses and diagnosis. Furthermore, ctDNA can be used to demonstrate pseudo-progression, monitor postoperative tumor status and guide adaptive treatment plans. The present study provides a comprehensive review of ctDNA, exploring its origins, metabolism, detection methods, clinical role and the current challenges associated with its application.

Can combined non-invasive methods improve diagnosis of lung cancer?

Background

Lung cancer is the most common malignancy in both gender. Early diagnosis is needed to reduce morbidity and mortality. There is a debate about the most accurate investigating modality for the diagnosis of lung cancer.

Methods

It is a retrospective cohort analysis to determine whether an approach of combined contrast-enhanced computed tomography (CECT) thorax with bronchoscopy method has higher sensitivity and specificity than combined CECT thorax with sputum cytology method. Records of patients with lung cancer who had visited the hospital within the last 6 months were retrospectively analyzed for their diagnostic modality. SPSS version 19 software was used for statistical analysis of the data. CECT scan thorax, bronchoscopy, and sputum cytology for lung cancer patients were analyzed. The CECT thorax plus bronchoscopy method was compared with the CECT thorax plus sputum cytology method. Their sensitivity, specificity, positive predictive value, negative predictive value, and accuracy in diagnosing lung cancer were analyzed.

Results

Sixty-two patients were considered, including 62.9% males with a mean age of 55.5 years. In patients diagnosed with lung cancer, CECT thorax combined with bronchoscopy method was found to have a sensitivity of 96.67% than CECT thorax combined with sputum cytology method with a sensitivity of 90% and the difference in sensitivity between all individual approaches as well as the combined method was statistically significant with a P = 0.00001 and Chi-square value of 86.5909 owing to the low sensitivity of sputum cytology. CECT thorax combined with sputum cytology approach had a better specificity than CECT thorax combined with bronchoscopy.

Conclusion

Combined CECT thorax with sputum cytology method has a better specificity in diagnosing lung cancer than combined CECT thorax with bronchoscopy method.

Sputum cell-free DNA for detection of alterations of multiple driver genes in lung adenocarcinoma

BACKGROUND

Sputum cell-free DNA (cfDNA) has been confirmed to be a valued surrogate sample for detection of EGFR mutations in patients with lung adenocarcinoma (LAC). Whether it is suitable for detection of mutations of multiple driver genes has not been reported.

METHODS

A total of 83 patients with LAC were enrolled and their sputum and paired tumor samples were collected. A next-generation sequencing (NGS)-based 10-gene panel was used to test sputum supernatant-derived cfDNA and paired tumor DNA. The sputum sediments were used for cytological evaluation.

RESULTS

The total positive rates of hotspot mutations of the 10 driver genes in sputum cfDNA and matched tissue samples were 65.1% and 77.1%, respectively. The overall detection sensitivity of variants in sputum cfDNA was 81.3% (95% confidence interval [CI], 69.2%, 89.5%) and the specificity was 100% (95% CI, 79.1%, 100%). The sensitivities of testing sputum cfDNA from patients with stage IIIB-IV was 87.0% (95% CI, 74.5%, 94.1%); the sensitivities of testing sputum cfDNA from patients with malignant sputum was 92.3% (95% CI, 78.0%, 98.0%); and the sensitivity of testing sputum cfDNA from patients with malignant sputum in stage IIIB-IV were 94.1% (95% CI, 78.9%, 99.0%).

CONCLUSIONS

This study demonstrated that sputum cfDNA were successfully used for the detection of multiple driver genes by NGS. Sputum cfDNA could be a valuable surrogate clinical sample for all-in-one test of mutations to guide target therapies, especially for patients with advanced LAC and malignant sputum.

Real-world analysis of the prognostic value of EGFR mutation detection in plasma ctDNA from patients with advanced non-small cell lung cancer

BACKGROUND

The plasma sample has emerged as a promising surrogate sample for EGFR mutation detection in advanced non-small cell lung cancer (NSCLC). In clinical practice, whether EGFR variants in baseline plasma ctDNA of advanced NSCLC can predict prognosis in addition to guiding targeted therapy remains to be further explored.

MATERIAL AND METHODS

In total, 315 NSCLC patients were retrospectively enrolled. EGFR mutation data from tissue detected by ARMS-PCR and paired plasma samples within 1 month of admission detected by SuperARMS or ARMS-PCR were collected. The correlation between baseline plasma ctDNA EGFR mutation status and survival was compared.

RESULTS

EGFR mutation detection rates in tumor samples and plasma samples were 65.1% (205/315) and 43.8% (138/315). Referred to tissue results, the consistent rate of test ctDNA EGFR alteration by SuperARMS was higher than that detected by ARMS (79.5% vs. 69.0%, p = 0.04), either in stage I-IIIA patients (85.7% vs. 50.0%, p = 0.4) or stage IIIB-IV patients (79.1% vs. 69.4%, p = 0.04). Patients' treatment status and pathological subtype were the two factors that affected plasma ctDNA EGFR alteration detection accuracy. The concordance in non-adenocarcinoma patients was obviously higher than that in adenocarcinoma (p = 0.02), and the concordance in treatment naïve patients was significantly higher than that in relapse patients (p = 0.047). In treatment naïve patients, the median PFS (mPFS) in plasma ctDNA EGFR-positive patients was shorter than that in plasma ctDNA EGFR negative patients (7.0 vs. 10.0 months, p = 0.01). In relapsed patients, the mPFS in plasma ctDNA EGFR-positive patients was 9.0 months versus 11.0 months in plasma ctDNA EGFR negative patients (p = 0.1).

CONCLUSIONS

A plasma sample could be an alternative for a molecular test when tissue samples was unavailable. The SuperARMS-PCR detection method has high sensitivity in real-world clinical practice. Furthermore, in patients with stage IIIB-IV, baseline plasma ctDNA EGFR mutation positivity not only guides targeted therapy but also predicts a worse prognosis.

Circulating tumor DNA in Hodgkin lymphoma

Somatic mutations of genes involved in NF-κB, PI3K/AKT, NOTCH, and JAK/STAT signaling pathways play an important role in the pathogenesis of Hodgkin lymphoma (HL). HL tumor cells form only about 5% of the tumor mass; however, it was shown that HL tumor-derived DNA could be detected in the bloodstream. This circulating tumor DNA (ctDNA) reflects the genetic profile of HL tumor cells and can be used for qualitative and quantitative analysis of tumor-specific somatic DNA mutations within the concept of liquid biopsy. Overall, the most frequently mutated gene in HL is STAT6; however, the exact spectrum of mutations differs between individual HL histological subtypes. Importantly, reduction of ctDNA plasma levels after initial treatment is highly correlated with prognosis. Therefore, ctDNA shows great promise as a novel tool for non-invasive tumor genome analysis for biomarker driven therapy as well as for superior minimal residual disease monitoring and treatment resistance detection. Here, we summarize the recent advancements of ctDNA analysis in HL with focus on ctDNA detection methodologies, genetic profiling of HL and its clonal evolution, and the emerging prognostic value of ctDNA.

Comprehensive characterization reveals sputum supernatant as a valuable alternative liquid biopsy for genome profiling in advanced non-small cell lung cancer

BACKGROUND

Sputum biopsies offer unique advantages such as non-invasiveness and convenient collection. The one investigation so far on sputum for genome profiling in advanced non-small cell lung cancer (aNSCLC) suggested promising performance. However, it remains undefined whether clinicohistologic characteristics were associated with performance and how this knowledge could help guide choice of liquid biopsy.

METHODS

Targeted sequencing with a 520-gene panel was performed on prospectively collected matched tumor tissue (TIS), plasma (PLA), and sputum supernatant (SPU) from 71 aNSCLC patients (NCT05034445). Genomic alteration detection was characterized in a series of aspects and interrogated for association with 14 clinicohistologic features. Nomograms were constructed with logistic regression for predicting the liquid biopsy type with greater sensitivity.

RESULTS

Compared with PLA, SPU showed comparable quality control metrics, mutation detection rate (SPU: 67.6%, PLA: 70.4%), concordance with tumor tissue (67.6% vs. 73.2%), and correlation with tissue-based tumor mutation burden levels (r = 0.92 vs. 0.94). For driver alterations, detection was less sensitive with SPU (50.0%) than PLA (63.5%) in the entire cohort but similarly or more sensitive in patients with centrally located lung tumors or smoking history or for altered ALK or KRAS. Two nomograms were constructed and enabled predicting the probability of superior sensitivity with SPU with moderate to borderline high accuracy.

CONCLUSION

In addition to demonstrating comparable performance in multiple aspects, this study is the first to propose nomograms for choosing liquid biopsy based on clinicohistologic characteristics. Future research is warranted to delineate the clinical utility of sputum for genome profiling.

Transcending Blood—Opportunities for Alternate Liquid Biopsies in Oncology

Simple Summary

Cell-free DNA—DNA that has been expelled from cells and can be isolated from blood plasma and other body fluids—is a useful tool in medicine, with applications as a biomarker in diagnosis, prognosis, disease profiling, and treatment selection. In oncology, the ease of access to the tumour genome is a major advantage of cell-free DNA, but while this has led to significant research in blood, other body fluids have not received equal attention. This review article summarises the current research into cell-free DNA in non-blood body fluids, highlighting its values and limitations, and suggesting the direction of future studies. We conclude that cell-free DNA from non-blood body fluids may provide additional information to supplement traditional biopsies, allowing informative and improved patient care across many cancer types.

Abstract

Cell-free DNA (cfDNA) is a useful molecular biomarker in oncology research and treatment, but while research into its properties in blood has flourished, there remains much to be discovered about cfDNA in other body fluids. The cfDNA from saliva, sputum, cerebrospinal fluid, urine, faeces, pleural effusions, and ascites has unique advantages over blood, and has potential as an alternative ‘liquid biopsy’ template. This review summarises the state of current knowledge and identifies the gaps in our understanding of non-blood liquid biopsies; where their advantages lie, where caution is needed, where they might fit clinically, and where research should focus in order to accelerate clinical implementation. An emphasis is placed on ascites and pleural effusions, being pathological fluids directly associated with cancer. We conclude that non-blood fluids are viable sources of cfDNA in situations where solid tissue biopsies are inaccessible, or only accessible from dated archived specimens. In addition, we show that due to the abundance of cfDNA in non-blood fluids, they can outperform blood in many circumstances. We demonstrate multiple instances in which DNA from various sources can provide additional information, and thus we advocate for analysing non-blood sources as a complement to blood and/or tissue. Further research into these fluids will highlight opportunities to improve patient outcomes across cancer types.

[Role and Significance of Bioactive Substances in Sputum in the Diagnosis of Lung Cancer]

肺癌是我国目前发病率最高的恶性肿瘤之一，其诊断的金标准需要进行组织活检的病理学检查或脱落细胞学检查，二者的有创性和敏感性限制了他们的使用。痰液中含有大量核酸、蛋白质，是肺功能的良好反映物，肺癌组织也会影响痰液中的生物成分，检测其中的生物活性物质可有助于肺癌的诊断。本文综合目前国内外的研究结果，对痰液中可用于肺癌诊断的生物活性物质做一综述。

Sputum cell-free DNA: Valued surrogate sample for the detection of EGFR exon 20 p.T790M mutation in patients with advanced lung adenocarcinoma and acquired resistance to EGFR-TKIs

BACKGROUND

Sputum cell-free DNA (cfDNA) is a valuable surrogate sample for assessing EGFR-sensitizing mutations in patients with advanced lung adenocarcinoma. Detecting EGFR exon 20 p.T790 M (p.T790 M) is much more challenging due to its limited availability in tumor tissues. Exploring sputum cfDNA as an alternative for liquid-based sample type in detecting p.T790 M requires potential improvement in clinical practice.

METHODS

A total of 34 patients with EGFR-sensitive mutation-positive lung adenocarcinoma and acquired resistance to the first generation of epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) were enrolled. The sputum samples, and paired tumors and/or plasma samples were tested for p.T790 M mutation and concordance of p.T790 M status among the three sample types was analyzed.

RESULTS

The overall concordance rate of p.T790 M mutation between sputum cfDNA and tumor tissue samples was 85.7%, with a sensitivity of 66.7% and a specificity of 100%. The sensitivity for detecting p.T790 M in sputum cfDNA was 100%, 66.7%, and 0% in the three sputum groups of malignant, satisfactory but no malignant cells, and unsatisfactory, respectively. The combined results of plasma cfDNA testing and sputum cfDNA testing further increased the sensitivity to 100% for p.T790 M detection in satisfactory but no malignant cells sputum group.

CONCLUSION

These findings revealed that cfDNA from malignant or satisfied but no malignant cells sputum is considered suitable for detecting p.T790 M mutation in patients with acquired resistance to first or second-generation EGFR-TKIs. The sputum cytological pathological evaluation-guided sputum cfDNA testing assists in significantly improving the sensitivity of p.T790 M detection, bringing significant value for the maximal application of third-generation EGFR-TKIs in second-line treatment.

Future Perspectives in Detecting EGFR and ALK Gene Alterations in Liquid Biopsies of Patients with NSCLC

Non-small-cell lung cancer (NSCLC) is a major cause of death worldwide. Alterations in such genes as EGFR and ALK are considered important biomarkers in NSCLC due to the existence of targeted therapies with specific tyrosine kinase inhibitors (TKIs). However, specific resistance-related mutations can occur during TKI treatment, which often result in therapy inefficacy. Liquid biopsies arise as a reliable tool for the early detection of these types of alterations, allowing a non-invasive follow-up of the patients. Furthermore, they can be essential for cancer screening, initial diagnosis and to check surgery success. Despite the great advantages of liquid biopsies in NSCLC and the high input that next-generation sequencing (NGS) approaches can provide in this field, its use in oncology is still limited. With improvement of assay sensitivity and the establishment of clinical guidelines for liquid biopsy analysis, it is expected that they will be used in routine procedures. This review focuses on the usefulness of liquid biopsies of NSCLC patients as a means to detect alterations in EGFR and ALK genes and in disease management, highlighting the impact of NGS methods.

Detection of EGFR mutation of pulmonary adenocarcinoma in sputum using droplet digital PCR

Background

It is still unclear whether epidermal growth factor receptor (EGFR) mutation of primary lung adenocarcinoma can be detected on sputum samples. This study aimed to examine EGFR mutations of primary lung adenocarcinoma in sputum samples using droplet digital polymerase chain reaction (ddPCR) and compare it with an EGFR mutation in surgically resected lung cancer.

Methods

Sputum was prospectively collected from the patients before complete resection of the primary lung cancer at Kanagawa Cancer Center from September 2014 to May 2016. ddPCR was performed to detect EGFR exon 21 L858R point mutation (Ex21) and EGFR exon 19 deletion mutation (Ex19) in sputum samples from patients with lung adenocarcinoma. The concordance of EGFR mutation status in sputum samples and tumors in surgically resected specimen was evaluated for each positive and negative cytology group.

Results

One hundred and eighteen patients with primary lung adenocarcinoma provided sputum samples. Sputum cytology was positive in 13 patients (11.0%). ddPCR detected two cases of Ex21 and two cases of Ex19 in sputum cytology positive cases. Compared to surgically resected specimens, the sensitivity, specificity, and positive predictive value of EGFR mutation (Ex19 and Ex21) detection were 80.0%, 100%, and 100%, respectively, in sputum cytology positive cases. In contrast, the sensitivity, specificity, and positive predictive value of EGFR mutation (Ex19 and Ex21) detection were 3.1%, 100%, and 100%, respectively, in sputum cytology negative cases.

Conclusions

EGFR mutations in primary lung adenocarcinoma can be detected with high sensitivity in sputum samples if sputum cytology is positive.

Multigene PCR using both cfDNA and cfRNA in the supernatant of pleural effusion achieves accurate and rapid detection of mutations and fusions of driver genes in patients with advanced NSCLC

Background

Pleural effusion from patients with advanced non‐small cell lung cancer (NSCLC) has been proved valuable for molecular analysis, especially when the tissue sample not available. However, simultaneous detection of multiple driver gene alterations especially the fusions is still challenging.

Methods

In this study, 77 patients with advanced NSCLC and pleural effusion were enrolled, 49 of whom had matched tumor tissues. Supernatants, cell sediments, and cell blocks were prepared from pleural effusion samples for detection of driver alterations by a PCR‐based 9‐gene mutation detection kit.

Results

Mutations in EGFR, KRAS, and HER2 were detected in DNA and cfDNA, fusions in ALK was detected in RNA and cfRNA. Compared with matched tumor tissue, the supernatant showed the highest overall sensitivity (81.3%), with 81.5% for SNV/Indels by cfDNA and 80% for fusions by cfRNA, followed by cell blocks (71.0%) and the cell sediments (66.7%). Within the group of treatment‐naïve patients or malignant cells observed in the cell sediments, supernatant showed higher overall sensitivity (89.5% and 92.3%) with both 100% for fusions.

Conclusions

CfDNA and cfRNA derived from pleural effusion supernatant have been successfully tested with a PCR‐based multigene detection kit. Pleural effusion supernatant seems a preferred material for detection of multigene alterations to guide treatment decision of advanced NSCLC.

Detection of EGFR Activating and Resistance Mutations by Droplet Digital PCR in Sputum of EGFR-Mutated NSCLC Patients

Background

Proof of the T790M resistance mutation is mandatory if patients with EGFR-mutated non-small cell lung cancer (NSCLC) progress under first- or second-generation tyrosine kinase inhibitor therapy. In addition to rebiopsy, analysis of plasma circulating tumor DNA is used to detect T790M resistance mutation. We studied whether sputum is another feasible specimen for detection of EGFR mutations.

Methods

Twenty-eight patients with advanced EGFR-mutated NSCLC were included during stable and/or progressive disease. The initial activating EGFR mutations (exon 19 deletions or L858R mutations) at stable disease and at progressive disease (together with T790M) were assessed in simultaneously collected plasma and sputum samples and detected by droplet digital polymerase chain reaction (ddPCR).

Results

Activating EGFR mutations were detected in 47% of the plasma samples and 41% of sputum samples during stable disease, and in 57% of plasma samples and 64% of sputum samples during progressive disease. T790M was detected in 44% of the plasma samples and 66% of the sputum samples at progressive disease. In ddPCR T790M-negative results for both specimens (plasma and sputum), negativity was confirmed by rebiopsy in 5 samples. Concordance rate of plasma and sputum for T790M was 0.86, with a positive percent agreement of 1.0 and a negative percent agreement of 0.80.

Conclusions

We demonstrated that EGFR mutation analysis with ddPCR is feasible in sputum samples. Combination of plasma and sputum analyses for detection of T790M in NSCLC patients with progressive disease increases the diagnostic yield compared with molecular plasma analysis alone.

Distinct profile of cell-free DNA in malignant pleural effusion of non-small cell lung cancer and its impact on clinical genetic testing

Cell-free DNA (cfDNA) in supernatant of pleural effusion from advanced NSCLC patients has been proved as surrogate sample detecting therapeutic targets as well as tumor mutation burden (TMB). As recently reported, cfDNA in pleural effusion supernatant is superior to plasma in TMB evaluation. It is reasonable to hypothesize that cfDNA profile in pleural effusion (PE) and plasma might be different. It remains to be elucidated why cfDNA in PE supernatant impacts on genetic analysis. Consequently, the approach dealing with cfDNA from PE supernatant might need to be different from that for plasma cfDNA in order to obtain accurate clinical genetic testing result. Methods: Pleural effusion samples from 32 patients with stage IV lung adenocarcinoma were collected. Supernatant and sediment were processed separately to extract Cell-free DNA as well as sediment DNA (PE-S). cfDNA from pleural effusion was analyzed by Agilent 2100 bioanalyzer. Libraries were prepared by 1) direct use of the total cfDNA without fragmentation step (PE-FL) or 2) use of full-length cfDNA fragmented to 150-250bp (PE-F), 3) use of cfDNA fragments enriched to ~167bp (PE-E167) as well as 4) use of cfDNA fragments larger than 500bp enriched (PE-E500). All samples were subjected to targeted next-generation sequencing (NGS) with a panel of 448 cancer-related genes as well as a panel of 10 NSCLC driver genes. Results: cfDNA were successfully extracted from 30 MPE samples. cfDNA displayed distinct profile in supernatant of malignant pleural effusion from that of plasma cfDNA. No statistical difference in detection of hotspot variations between PE-E167 and PE-F by 448-gene or 10-gene panel. While TMB from PE-F samples was significantly higher than that from PE-E167 and PE-FL. Higher TMB from PE-F was resulted from cancer-unspecific variants with low allele frequency (0.1%-1%) which were mainly introduced by long-fragment cfDNA. Similar genetic profile was observed between paired cfDNA of PE-FL and cfDNA of PE-E167. Conclusion: Long-fragment cfDNA in the PE supernatant will introduce low abundant cancer unrelated variants which leads overestimation of TMB. Paired PE-FL and PE-E167 gave comparable outcomes. Direct use of the total cfDNA without fragmentation step (PE-FL) is recommended for library preparation of NGS testing in clinical practice to exclude interference from long fragments of the cfDNA.

Donor-Derived Cell-Free DNA in Kidney Transplantation as a Potential Rejection Biomarker: A Systematic Literature Review

Kidney transplantation (KTx) is the best treatment method for end-stage kidney disease. KTx improves the patient's quality of life and prolongs their survival time; however, not all patients benefit fully from the transplantation procedure. For some patients, a problem is the premature loss of graft function due to immunological or non-immunological factors. Circulating cell-free DNA (cfDNA) is degraded deoxyribonucleic acid fragments that are released into the blood and other body fluids. Donor-derived cell-free DNA (dd-cfDNA) is cfDNA that is exogenous to the patient and comes from a transplanted organ. As opposed to an invasive biopsy, dd-cfDNA can be detected by a non-invasive analysis of a sample. The increase in dd-cfDNA concentration occurs even before the creatinine level starts rising, which may enable early diagnosis of transplant injury and adequate treatment to avoid premature graft loss. In this paper, we summarise the latest promising results related to cfDNA in transplant patients.

Technical and Methodological Aspects of Cell-Free Nucleic Acids Analyzes

Analyzes of cell-free nucleic acids (cfNAs) have shown huge potential in many biomedical applications, gradually entering several fields of research and everyday clinical care. Many biological properties of cfNAs can be informative to gain deeper insights into the function of the organism, such as their different types (DNA, RNAs) and subtypes (gDNA, mtDNA, bacterial DNA, miRNAs, etc.), forms (naked or vesicle bound NAs), fragmentation profiles, sequence composition, epigenetic modifications, and many others. On the other hand, the workflows of their analyzes comprise many important steps, from sample collection, storage and transportation, through extraction and laboratory analysis, up to bioinformatic analyzes and statistical evaluations, where each of these steps has the potential to affect the outcome and informational value of the performed analyzes. There are, however, no universal or standard protocols on how to exactly proceed when analyzing different cfNAs for different applications, at least according to our best knowledge. We decided therefore to prepare an overview of the available literature and products commercialized for cfNAs processing, in an attempt to summarize the benefits and limitations of the currently available approaches, devices, consumables, and protocols, together with various factors influencing the workflow, its processes, and outcomes.

Liquid Biopsy of Non-Plasma Body Fluids in Non-Small Cell Lung Cancer: Look Closer to the Tumor!

Liquid biopsy is a rapidly emerging field due to an increasing number of oncogenic drivers and a better understanding of resistance mechanisms to targeted therapies in non-small cell lung cancer (NSCLC). The sensitivity of the most widely used blood-based assays is, however, limited in particular in cases of low tumor volume where shed of tumor-derived material can be limited. A negative result thus requires biopsy confirmation using minimally invasive sampling procedures that can result in small specimens, which are often not suitable for genotyping. Liquid biopsy is not limited to plasma, and tumor DNA circulating in other body fluids such as urine, pleural fluid, cerebrospinal fluid, or cytology specimen-derived supernatant can be exploited. In comparison to cell blocks, these fluids in close contact to the tumor may contain a more abundant and less analytically demanding tumor DNA. In this review, we discuss the potential applications of circulating tumor DNA derived from cytology samples in NSCLC, from early stage (screening, nodule characterization) to metastatic disease.