Gefitinib treatment in EGFR mutated caucasian NSCLC: circulating-free tumor DNA as a surrogate for determination of EGFR status

Estimation of cell-free circulating EGFR mutation concentration predicts outcomes in NSCLC patients treated with EGFR-TKIs

Detection of circulating tumor DNA using droplet digital polymerase chain reaction (ddPCR) is a highly-sensitive, minimally invasive alternative to serial biopsies for assessment and management of cancer. We used ddPCR to assess the utility of measuring plasma concentrations of common epidermal growth factor receptor (EGFR) mutations (L858R, exon 19 deletion, and T790M) in 57 non-small cell lung cancer (NSCLC) patients treated with EGFR tyrosine kinase inhibitors (EGFR-TKIs). High baseline plasma EGFR mutation (pEGFRmut) concentrations were associated with shorter progression-free survival (8.43 months) than low baseline pEGFRmut (16.23 months; p = 0.0019). By contrast, there were no differences in tumor shrinkage or overall survival between groups. During EGFR-TKI treatment, pEGFRmut levels decreased to zero in 89.58% of patients. Twenty-five of the 27 patients who progressed had basal pEGFRmut, and 18 also had circulating T790M. All 20 patients with dramatic progression (according to a categorization system for EGFR-TKIs failure) had basal pEGFRmut, and 13 had T790M mutation at progression. These results support the use of ddPCR for analysis of plasma EGFR mutations for prediction of PFS and to monitor clinical responses to EGFR-TKIs in NSCLC patients.

The resistance mechanisms and treatment strategies for EGFR-mutant advanced non-small-cell lung cancer

Epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKI) have been established as the standard therapy for EGFR-sensitizing mutant advanced non-small-cell lung cancer (NSCLC). However, patients ultimately develop resistance to these drugs. There are several mechanisms of both primary and secondary resistance to EGFR-TKIs. The primary resistance mechanisms include point mutations in exon 18, deletions or insertions in exon 19, insertions, duplications and point mutations in exon 20 and point mutation in exon 21 of EGFR gene. Secondary resistance to EGFR-TKIs is due to emergence of T790M mutation, activation of alternative signaling pathways, bypassing downstream signaling pathways and histological transformation. Strategies to overcome these intrinsic and acquired resistance mechanisms are complex. With the development of the precision medicine for advanced NSCLC, available systemic and local treatment options have expanded, requiring new clinical algorithms that take into account resistance mechanism. Though combination therapy is emerging as the standard of to overcome resistance mechanisms. Personalized treatment modalities based on molecular diagnosis and monitoring is essential for disease management. Emerging data from the ongoing clinical trials on combination therapy of third generation TKIs and antibodies in EGFR mutant NSCLC are promising for better survival outcomes.

Intercalating and maintenance gefitinib plus chemotherapy versus chemotherapy alone in selected advanced non-small cell lung cancer with unknown EGFR status

Epidermal growth factor receptor tyrosine-kinase inhibitors (EGFR-TKIs) are standard treatment for advanced non-small cell lung cancer (NSCLC) patients with epidermal growth factor receptor (EGFR) mutation. However, EGFR mutation testing is not attainable in approximately 20% of patients. The current study examined intercalating and maintaining gefitinib treatment in stage IIIB/IV non-squamous NSCLC, never or former light smoking patients with unknown EGFR mutation status. Briefly, 219 patients who achieved stable disease (SD) with gemcitabine (1250 mg/m²) plus carboplatin (5 AUC) were randomized at 1:1 ratio to continue chemotherapy (n = 110) or intercalating gefitinib (250 mg/day on days 15–25 of each cycle until disease progress (n = 109). Progression-free survival (PFS) was 9.7 vs. 4.2 month in the gefitinib vs. control arm (HR: 0.41, 95% CI: 0.31–0.56; P < 0.001). Overall survival (OS) was also longer in the gefitinib arm (20.1 vs. 15.4 months; HR: 0.68; 95% CI 0.48–0.97; P = 0.0323). Adverse events, including diarrhea, dermal reaction and thrombocytopenia, were more common in the gefitinib arm. In conclusion, intercalating and maintenance gefitinib treatment is a viable option for advanced NSCLC patients with unknown EGFR mutation status in subpopulations with high EFGR mutation rate.

EGFR TKI as first-line treatment for patients with advanced EGFR mutation-positive non-small-cell lung cancer

After the discovery of activating mutations in EGFR, EGFR tyrosine kinase inhibitors (TKIs) have been introduced into the first-line treatment of non-small-cell lung cancer (NSCLC). A series of studies have shown that EGFR TKI monotherapy as first-line treatment can benefit NSCLC patients harbouring EGFR mutations. Besides, combination strategies based on EGFR TKIs in the first line treatment have also been proved to delay the occurrence of resistance. In this review, we summarize the scientific literature and evidence of EGFR TKIs as first-line therapy from the first-generation EGFR TKIs to conceptually proposed fourth-generation EGFR TKI, and also recommend the application of monotherapy and combination therapies of the EGFR-based targeted therapy with other agents such as chemotherapy, anti-angiogenic drugs and immunecheckpoint inhibitors.

Analyzing epidermal growth factor receptor mutation status changes in advanced non-small-cell lung cancer at different sampling time-points of blood within one day

BACKGROUND

We investigated whether different sampling time-points within one day would influence epidermal growth factor receptor mutation (EGFRm) status in plasma and evaluated the clinical outcomes according to the quantity analysis of EGFRm in circulating tumor DNA (ctDNA) in non-small-cell lung cancer (NSCLC).

METHODS

EGFR-tyrosine kinase inhibitor naïve advanced NSCLC patients who carried EGFRm in both tissues and ctDNA were enrolled in this study. Plasma samples were collected at three time-points within one day (at 8 am, 11 am and 2 pm) for EGFRm analysis by droplet digital PCR.

RESULTS

Twenty-two advanced NSCLC patients were enrolled in the study. In a total of 66 blood specimens, the median EGFRm frequency was 7.13% (range 0-35.09%), and among them six specimens had less than 1.0% EGFRm frequency. Moreover, one time-point blood specimen did not display any EGFRm, even by droplet digital PCR. The frequency of EGFRm changed dynamically across different time-points within one day, but the differences were not significant (P = 0.557). We observed that patients with a relatively high frequency of EGFRm (>6.76%) had a better response to gefitinib (P = 0.024).

CONCLUSION

The release of ctDNA maybe a temporal heterogenous process. The different sampling time-points within one day did not seem to influence EGFRm status in ctDNA. The relative EGFRm frequency in ctDNA could predict a benefit of EGFR-tyrosine kinase inhibitor treatment for advanced NSCLC patients.

Plasma genotyping in patients with non-small-cell lung cancer: simplifying or confusing the diagnosis?

The identification of driver mutations in patients with advanced non-small-cell lung cancer has changed the treatment outcomes for patients with actionable driver mutations. Lack of tissue at diagnosis, however, remains a central obstacle in making optimal treatment decisions in patients with advanced disease. Although the US FDA has approved one plasma-based test for detecting epidermal growth factor receptor mutations in patients with advanced stage disease, sensitivity of these assays remains mediocre, necessitating additional tissue testing and possible delays in patients with negative results. Serial monitoring for response and early detection of acquired resistance to targeted therapies is also possible with cell-free DNA, however the benefit of switching therapy prior to detection of changes on imaging is unknown currently.

EGFR T790M ctDNA testing platforms and their role as companion diagnostics: Correlation with clinical outcomes to EGFR-TKIs

Somatic mutation in the epidermal growth factor receptor (EGFR) predict clinical response to EGFR tyrosine kinase inhibitors in non-small cell lung cancer (NSCLC) and is a promising target for personalised medicine. EGFR mutations have prognostic value. Initially patients respond well to tyrosine kinase inhibitors but finally they would develop resistance and about 50% of this resistance can be attributed to the emergence of EGFR resistant mutation, T790M. This necessitates the need for genetic testing for clinical management of patients. Molecular testing has become the standard of care in patients with NSCLCs based on the recommendations of standard guidelines. Though there are several platforms for EGFR mutation detection, highly sensitive platforms for clinical applicability as companion diagnostics for ctDNA based testing are emerging. Due to the dynamic changes in the T790M mutation during tyrosine kinase inhibitor (TKI) treatment, real-time monitoring of these genetic alterations is mandate for planning treatment strategies. With the advent of third generation TKIs that potentially target T790M, improvement in clinical outcome is documented in patients with NSCLCs. Managing these outcomes with appropriate companion diagnostics using ctDNA in early detection of these genetic alterations will improve patient care.

Application of Plasma Genotyping Technologies in Non-Small Cell Lung Cancer: A Practical Review

The rational treatment of metastatic NSCLC hinges on the timely detection of potentially targetable genomic alterations to guide therapy. Recent advances in highly sensitive genotyping technologies have allowed for development of novel plasma genotyping assays that are capable of noninvasively detecting targetable alterations in plasma cell-free DNA without reliance on traditional tissue genotyping. The rapid development of plasma genotyping has led to an explosion in the number of assay platforms available from both commercial and laboratory sources. The sheer number of such platforms has led to confusion among oncologists as to both the test characteristics and limitations of individual plasma genotyping assays and the clinical context in which these tests may be utilized either alone or in combination with traditional tissue genotyping. Reliable data from prospective validation against a tissue genotyping reference standard are available for only a limited number of platforms. Careful retrospective validation of alternative platforms utilizing paired tissue and plasma specimens collected under the auspices of clinical trials represent an alternative but reliable validation strategy. A consistent trend among these well-validated plasma genotyping assays has been the observation of high specificity and positive predictive value and more limited sensitivity. At present, validated assays can be considered actionable in instances in which a targetable genomic alteration is detected or an alternative nontargetable driver mutation is detected and can be used to infer the absence of one of the former.

Multiplex picoliter-droplet digital PCR for quantitative assessment of EGFR mutations in circulating cell-free DNA derived from advanced non-small cell lung cancer patients

To explore the possible diagnostic value of liquid biopsy, two multiplex panels using picoliter-droplet digital polymerase chain reaction (ddPCR) were established to quantitatively assess the epidermal growth factor receptor (EGFR) mutations in cell‑free DNA (cfDNA) extracted from the plasma of advanced non‑small cell lung cancer (NSCLC) patients. Plasma samples derived from 22 patients with stage IIIB/IV NSCLC harboring EGFR mutations in matched tumor tissues confirmed by amplification refractory mutation system (ARMS) analysis were subjected to two multiplex ddPCR panels to assess the abundance of tyrosine kinase inhibitor (TKI) ‑sensitive (19DEL, L858R) and TKI‑resistant (T790 M) mutations. Fluctuations in EGFR mutant abundance were monitored by either of the multiplex ddPCR panels for three patients undergoing EGFR‑TKI treatment, with serial plasma sample collections over 2 months. The multiplex ddPCR panels applied to plasma cfDNA from advanced NSCLC patients achieved a total concordance rate of 80% with the EGFR mutation profiles obtained by ARMS from matched biopsy tumor specimens (90% for 19DEL, 95% for L858R, 95% for T790M, respectively) and revealed additional mutant alleles in two subjects. The respective sensitivity and specificity were 90.9 and 88.9% for 19DEL, 87.5 and 100% for L858R, 100 and 93.8% for T790M. The fluctuations of EGFR mutant abundance in serial plasma cfDNA were in accordance with the changes in tumor size as assessed by imaging scans. The authors demonstrated the utility of multiplex ddPCR panels with ultra‑sensitivity for quantitative analysis of EGFR mutations in plasma cfDNA and obtained promising usefulness in EGFR‑TKI decision‑making for advanced NSCLC patients.

Osimertinib in patients with advanced epidermal growth factor receptor T790M mutation-positive non-small cell lung cancer: rationale, evidence and place in therapy

The identification of epidermal growth factor receptor (EGFR) mutations represented a fundamental step forward in the treatment of advanced non-small cell lung cancer (NSCLC) as they define a subset of patients who benefit from the administration of specifically designed targeted therapies. The inhibition of mutant EGFR through EGFR-tyrosine kinase inhibitors (TKIs), either reversible, first-generation gefitinib and erlotinib, or irreversible, second-generation afatinib, has dramatically improved the prognosis of patients harboring this specific genetic alteration, leading to unexpected clinical benefit. Unfortunately, virtually all patients who initially respond to treatment develop acquired resistance to EGFR-TKIs within 9-14 months. The EGFR T790M secondary mutation has emerged as a cause of treatment failure in approximately 60% of resistant cases. To date, several compounds designed with the aim to overcome T790M-mediated resistance are under clinical investigation. The aim of this review is to discuss emerging data regarding the third-generation EGFR-TKI, osimertinib, for the treatment of EGFR T790M mutant advanced NSCLC.

EGFR Mutation Analysis for Prospective Patient Selection in Two Phase II Registration Studies of Osimertinib

INTRODUCTION

Osimertinib is an oral, central nervous system-active, EGFR tyrosine kinase inhibitor (TKI) for the treatment of EGFR T790M-positive advanced NSCLC. Here we have evaluated EGFR mutation frequencies in two phase II studies of osimertinib (AURA extension and AURA2).

METHODS

After progression while receiving their latest line of therapy, patients with EGFR mutation-positive advanced NSCLC provided tumor samples for mandatory central T790M testing for the study selection criteria. Tumor tissue mutation analysis for patient selection was performed with the Roche cobas EGFR Mutation Test (European Conformity-in vitro diagnostic, labeled investigational use only) (Roche Molecular Systems, Pleasanton, CA). Patients should not have been prescreened for T790M mutation status. The cobas test results were compared with those of the MiSeq next-generation sequencing system (Illumina, San Diego, CA), which was used as a reference method.

RESULTS

Samples from 324 and 373 patients screened for AURA extension and AURA2, respectively, produced valid cobas test results. The T790M detection rates were similar between AURA extension and AURA2 (64% and 63%, respectively). The pooled T790M rate was 63%, with no difference by ethnicity (63% for Asian and non-Asian patients alike) or immediately prior treatment with an EGFR TKI (afatinib, 69%; erlotinib, 69%; and gefitinib, 63%). A higher proportion of patients had T790M detected against a background of exon 19 deletions versus L858R mutation (73% versus 58% [p = 0.0002]). In both trials the cobas test demonstrated high sensitivity (positive percent agreement) and specificity (negative percent agreement) for T790M detection when compared with the next-generation sequencing reference method: positive percent agreement of 91% versus 89% and negative percent agreement of 97% versus 98%.

CONCLUSIONS

In both trials, the rate of detection of T790M mutation in patients with advanced NSCLC was approximately 63% and was unaffected by immediately prior treatment with an EGFR TKI or ethnicity.

Quantitative cell-free circulating EGFR mutation concentration is correlated with tumor burden in advanced NSCLC patients

OBJECTIVES

Droplet digital polymerase chain reaction (ddPCR) has shown sufficient concordance in detecting plasma epidermal growth factor receptor (EGFR) status in non-small cell lung cancer (NSCLC), compared to tumor tissues. However, the clinical significance of the quantitative plasma mutated EGFR concentration remains unknown. The purpose of this study was to explore the relationship of plasma mutated EGFR concentration with tumor burden in advanced NSCLC patients.

MATERIALS AND METHODS

Using ddPCR, plasma DNA samples prior to administration of therapies from 113 consecutive NSCLC patients were analyzed for EGFR L858R substitution and deletion of exon19 (ex19del). Plasma EGFR status was compared to tumor EGFR status to determine concordance. Then, we assessed the correlation of plasma mutated EGFR concentrations with tumor burden and other tumor characteristics.

RESULTS AND CONCLUSION

Compared to tumor EGFR, the concordance rate of plasma and tissue EGFR status was 86.73%. Of the 64 patients who harbored tumor EGFR mutation, plasma mutated EGFR concentrations significantly correlated with number of metastatic sites (Spearman's r=0.4954, p<0.0001), number of lesions (Spearman's r=0.4484, p=0.0002), and sum of measurable lesions' diameters (Spearman's r=0.3539, p=0.0048). Number of metastatic sites was independently associated with mutated EGFR concentration in multiple linear regression. Besides, plasma mutated EGFR concentrations were significantly higher in those with extensive tumor burden (median concentration, 386.9 vs. 13.4copies/mL; p<0.0001) and stage IV disease (median concentration, 244.2 vs. 0copies/mL; p=0.0252). In conclusion, mutated plasma EGFR concentration determined by ddPCR analysis significantly correlated with tumor burden.

Current status of research and treatment for non-small cell lung cancer in never-smoking females

Lung cancer is the leading cause of cancer-related deaths worldwide with over 1 million deaths each year. The overall prognosis of lung cancer patients remains unsatisfactory, with a 5-year overall survival rate of less than 15%. Although most lung cancers are a result of smoking, approximately 25% of lung cancer cases worldwide are not attributable to tobacco use. Notably, more than half of the lung cancer cases in women occur in non-smokers. Among non-small-cell lung cancer (NSCLC) cases, cigarette-smokers have a greater association with squamous cell carcinoma than adenocarcinoma, which is more common in non-smokers. These findings imply that specific molecular and pathological features may associate with lung adenocarcinoma arising in non-smoker female patients. Over the past decade, whole genome sequencing and other '-omics' technologies led to the discovery of pathogenic mutations that drive tumor cell formation. These technological developments may enable tailored patient treatments throughout the course of their disease, potentially leading to improved patient outcomes. Some clinical and laboratory studies have shown success outcomes using epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK) tyrosine kinase inhibitors (TKI) in patients with EGFR mutations and ALK rearrangements, respectively. In fact, these 2 mutations are predominantly present in female non-smokers with adenocarcinoma. Immunotherapy has also recently emerged as a major therapeutic modality in NSCLC. In this review, we summarize the current understanding of NSCLC biology and new therapeutic molecular targets, focusing on the pathogenesis of non-smoker female NSCLC patients.

Detection of activating and acquired resistant mutation in plasma from EGFR-mutated NSCLC patients by peptide nucleic acid (PNA) clamping-assisted fluorescence melting curve analysis

This study was designed to prospectively examine whether peptide nucleic acid clamping-assisted fluorescence melting curve analysis (PANAMutyper™) is feasible for the detection of activating and acquired resistant epidermal growth factor receptor (EGFR) mutation in plasma. Patients with non-small cell lung cancer harboring activating EGFR mutations who were scheduled to undergo EGFR-tyrosine kinase inhibitors (EGFR-TKIs) were enrolled between September 2011 and March 2015. A total of 102 patients with EGFR-mutated lung cancer were enrolled, 53 had available plasma samples at disease progression, and 28 underwent serial plasma sampling during EGFR-TKI treatment. EGFR-TKI-sensitizing and T790M mutations were detected in the plasma of 68.6% (70/102) at baseline and 30.2% (16/53) at disease progression, respectively. The concordance rates for matched tissue and plasma samples were 80.4% and 90.2% for E19del and L858R mutations at baseline and 56.3% for T790M mutation at disease progression. The sustained presence of plasma EGFR mutations four weeks after EGFR-TKI predicted a poor objective response rate (30.0% vs. 87.5%, P = 0.025), as well as worse progression-free survival (hazard ratio [HR], 4.381) and overall survival (HR, 5.475). Longitudinal analysis could detect T790M mutations earlier than disease progression based on imaging study (median time from appearance of T790M in plasma samples to progression at imaging scan, 103 days). In conclusion, PANAMutyper™ is reliable for detecting activating and acquired resistant EGFR mutation in plasma, and predicts responses to EGFR-TKI via longitudinal monitoring of EGFR mutation during treatment.

Plasma ctDNA Analysis for Detection of the EGFR T790M Mutation in Patients with Advanced Non-Small Cell Lung Cancer

INTRODUCTION

Tumor biopsies for detecting EGFR mutations in advanced NSCLC are invasive, costly, and not always feasible for patients with late-stage disease. The clinical utility of the cobas EGFR Mutation Test v2 (Roche Molecular Systems, Inc., Pleasanton, CA) with plasma samples from patients with NSCLC at disease progression after previous EGFR tyrosine kinase inhibitor therapy was investigated to determine eligibility for osimertinib treatment.

METHODS

Matched tumor tissue and plasma samples from patients screened for the AURA extension and AURA2 phase II studies were tested for EGFR mutations by using tissue- and plasma-based cobas EGFR mutation tests. Plasma test performance was assessed by using the cobas tissue test and a next-generation sequencing method (MiSeq [Illumina Inc., San Diego, CA]) as references. The objective response rate, measured by blinded independent central review, was assessed in patients receiving osimertinib with a plasma T790M mutation-positive status.

RESULTS

During screening, 551 patients provided matched tumor tissue and plasma samples. Pooled analysis of the positive and negative percent agreements between the cobas plasma and tissue tests for detection of T790M mutation were 61% and 79%, respectively. Comparing cobas plasma test with next-generation sequencing demonstrated positive and negative percent agreements of 90% or higher. The objective response rate was 64% (95% confidence interval: 57-70) in T790M mutation-positive patients by both cobas tissue and plasma tests (evaluable for response).

CONCLUSIONS

The cobas plasma test detected the T790M mutation in 61% of tumor tissue T790M mutation-positive patients. To mitigate the risk of false-negative plasma results, patients with a negative plasma result should undergo a tissue test where feasible.

Post surgery circulating free tumor DNA is a predictive biomarker for relapse of lung cancer

Cancer cells release DNA fragments into plasma as circulating free DNA (cfDNA). However, quantitative measurement of tumor-derived DNA in cfDNA remains challenge. The purpose of this study was to quantitatively assess tumor-derived DNA in lung cancer patients. By optimizing competitive allele-specific TaqMan PCR (CAST-PCR), we assessed the copy number of mutated Kirsten rat sarcoma viral oncogene homolog (KRAS) and epidermal growth factor receptor (EGFR) alleles in the pre/post surgery plasma of 168 lung cancer patients. An absolute quantitative PCR method was developed to assess the number of total cfDNA. All mutations detected in tumors were also found in the plasma after surgery. At the time of 30 days after surgery, EGFR mutation of circulating cell-free DNA was detected only in two patients who recurred in 4 months after surgery. Compared to that of normal control at 30 days after surgery, five patients who recurred in 4 months had significantly higher circulating cell-free DNA (P < 0.001), whereas six patients who recurred after 4 months (P = 0.207) and five patients without recurrence (P = 0.901) demonstrated significantly lower circulating cell-free DNA. Our findings suggest that cfDNA analysis in plasma is an alternative and supplement to tissue analysis and hold promise for clinical application. Stratification of patients according to cfDNA levels at 30 days after surgery might be helpful in selecting lung cancer patients for adjuvant therapy after surgery.

Liquid biopsies come of age: towards implementation of circulating tumour DNA

Improvements in genomic and molecular methods are expanding the range of potential applications for circulating tumour DNA (ctDNA), both in a research setting and as a 'liquid biopsy' for cancer management. Proof-of-principle studies have demonstrated the translational potential of ctDNA for prognostication, molecular profiling and monitoring. The field is now in an exciting transitional period in which ctDNA analysis is beginning to be applied clinically, although there is still much to learn about the biology of cell-free DNA. This is an opportune time to appraise potential approaches to ctDNA analysis, and to consider their applications in personalized oncology and in cancer research.

Guide to detecting epidermal growth factor receptor (EGFR) mutations in ctDNA of patients with advanced non-small-cell lung cancer

Cancer treatment is evolving towards therapies targeted at specific molecular abnormalities that drive tumor growth. Consequently, to determine which patients are eligible, accurate assessment of molecular aberrations within tumors is required. Obtaining sufficient tumor tissue for molecular testing can present challenges; therefore, circulating free tumor-derived DNA (ctDNA) found in blood plasma has been proposed as an alternative source of tumor DNA. The diagnostic utility of ctDNA for the detection of epidermal growth factor receptor (EGFR) mutations harbored in tumors of patients with advanced non-small-cell lung cancer (NSCLC) is supported by the results of several large studies/meta-analyses. However, recent real-world studies suggest that the performance of ctDNA testing varies between geographic regions/laboratories, demonstrating the need for standardized guidance. In this review, we outline recommendations for obtaining an accurate result using ctDNA, relating to pre-analytical plasma processing, ctDNA extraction, and appropriate EGFR mutation detection methods, based on clinical trial results. We conclude that there are several advantages associated with ctDNA, including the potential for repeated sampling - particularly following progression after first-line tyrosine kinase inhibitor (TKI) therapy, as TKIs targeting resistance mutations (eg T790M) are now approved for use in the USA/EU/Japan (at time of writing). However, evidence suggests that ctDNA does not allow detection of EGFR mutations in all patients with known mutation-positive NSCLC. Therefore, although tumor tissue should be the first sample choice for EGFR testing at diagnosis, ctDNA is a promising alternative diagnostic approach.

Plasma epidermal growth factor receptor mutation testing with a chip-based digital PCR system in patients with advanced non-small cell lung cancer

OBJECTIVES

Epidermal growth factor receptor (EGFR) mutation testing is a companion diagnostic to determine eligibility for treatment with EGFR tyrosine kinase inhibitors (EGFR-TKIs) in non-small cell lung cancer (NSCLC). Recently, plasma-based EGFR testing by digital polymerase chain reaction (dPCR), which enables accurate quantification of target DNA, has shown promise as a minimally invasive diagnostic. Here, we aimed to evaluate the accuracy of a plasma-based EGFR mutation test developed using chip-based dPCR-based detection of 3 EGFR mutations (exon 19 deletions, L858R in exon 21, and T790M in exon 20).

MATERIALS AND METHODS

Forty-nine patients with NSCLC harboring EGFR-activating mutations were enrolled, and circulating free DNAs (cfDNAs) were extracted from the plasma of 21 and 28 patients before treatment and after progression following EGFR-TKI treatment, respectively.

RESULTS

Using reference genomic DNA containing each mutation, the detection limit of each assay was determined to be 0.1%. The sensitivity and specificity of detecting exon 19 deletions and L858R mutations, calculated by comparing the mutation status in the corresponding tumors, were 70.6% and 93.3%, and 66.7% and 100%, respectively, showing similar results compared with previous studies. T790M was detected in 43% of 28 cfDNAs after progression with EGFR-TKI treatment, but in no cfDNAs before the start of the treatment.

CONCLUSION

This chip-based dPCR assay can facilitate detection of EGFR mutations in cfDNA as a minimally invasive method in clinical settings.

The first liquid biopsy test approved. Is it a new era of mutation testing for non-small cell lung cancer?

Specific mutations in epidermal growth factor receptor (EGFR) gene are predictive for response to the EGFR tyrosine kinase inhibitors (TKIs) in non-small cell lung cancer patients (NSCLC). According to international guidelines, the molecular testing in patients with advanced NSCLC of a non-squamous subtype is recommended. However, obtain a tissue sample could be challenging. Liquid biopsy allows to determine patients suitable for EGFR-targeted therapy by analysis of circulating-free tumor DNA (cfDNA) in peripheral blood samples and might replace tissue biopsy. It allows to acquire a material in convenient minimally invasive manner, is easily repeatable, could be used for molecular identification and molecular changes monitoring. Many studies show a high concordance rate between tissue and plasma samples testing. When U.S. Food and Drug Administration (FDA) approved the first liquid biopsy test, analysis of driver gene mutation from cfDNA becomes a reality in clinical practice for patients with NSCLC.

Prospective Validation of Rapid Plasma Genotyping for the Detection of EGFR and KRAS Mutations in Advanced Lung Cancer

IMPORTANCE

Plasma genotyping of cell-free DNA has the potential to allow for rapid noninvasive genotyping while avoiding the inherent shortcomings of tissue genotyping and repeat biopsies.

OBJECTIVE

To prospectively validate plasma droplet digital PCR (ddPCR) for the rapid detection of common epidermal growth factor receptor (EGFR) and KRAS mutations, as well as the EGFR T790M acquired resistance mutation.

DESIGN, SETTING, AND PARTICIPANTS

Patients with advanced nonsquamous non-small-cell lung cancer (NSCLC) who either (1) had a new diagnosis and were planned for initial therapy or (2) had developed acquired resistance to an EGFR kinase inhibitor and were planned for rebiopsy underwent initial blood sampling and immediate plasma ddPCR for EGFR exon 19 del, L858R, T790M, and/or KRAS G12X between July 3, 2014, and June 30, 2015, at a National Cancer Institute-designated comprehensive cancer center. All patients underwent biopsy for tissue genotyping, which was used as the reference standard for comparison; rebiopsy was required for patients with acquired resistance to EGFR kinase inhibitors. Test turnaround time (TAT) was measured in business days from blood sampling until test reporting.

MAIN OUTCOMES AND MEASURES

Plasma ddPCR assay sensitivity, specificity, and TAT.

RESULTS

Of 180 patients with advanced NSCLC (62% female; median [range] age, 62 [37-93] years), 120 cases were newly diagnosed; 60 had acquired resistance. Tumor genotype included 80 EGFR exon 19/L858R mutants, 35 EGFR T790M, and 25 KRAS G12X mutants. Median (range) TAT for plasma ddPCR was 3 (1-7) days. Tissue genotyping median (range) TAT was 12 (1-54) days for patients with newly diagnosed NSCLC and 27 (1-146) days for patients with acquired resistance. Plasma ddPCR exhibited a positive predictive value of 100% (95% CI, 91%-100%) for EGFR 19 del, 100% (95% CI, 85%-100%) for L858R, and 100% (95% CI, 79%-100%) for KRAS, but lower for T790M at 79% (95% CI, 62%-91%). The sensitivity of plasma ddPCR was 82% (95% CI, 69%-91%) for EGFR 19 del, 74% (95% CI, 55%-88%) for L858R, and 77% (95% CI, 60%-90%) for T790M, but lower for KRAS at 64% (95% CI, 43%-82%). Sensitivity for EGFR or KRAS was higher in patients with multiple metastatic sites and those with hepatic or bone metastases, specifically.

CONCLUSIONS AND RELEVANCE

Plasma ddPCR detected EGFR and KRAS mutations rapidly with the high specificity needed to select therapy and avoid repeat biopsies. This assay may also detect EGFR T790M missed by tissue genotyping due to tumor heterogeneity in resistant disease.

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.

Circulating tumor cells and DNA for real-time EGFR detection and monitoring of non-small-cell lung cancer

AIM

We investigate the suitability of circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) in non-small-cell lung cancer management, which is challenging in conventional biopsies.

MATERIALS & METHODS

We performed serial blood extraction from 120 patients of varying EGFR status. Molecular profiling was performed using droplet digital PCR and correlated to survival outcome.

RESULTS

Overall, we observed 95% agreement using CTCs and ctDNA with conventional tissue biopsies, which indicated the disease's close correlation. The mutant signature was stable and captured the dynamic changes during treatment. It aided to stratify patients with worse survival outcome.

CONCLUSION

CTCs and ctDNA can complement current disease management. We demonstrated its effectiveness in continuous disease profiling, which is critical for clinical decision-making.

Treatment in EGFR-mutated Non-small Cell Lung Cancer: How to Block the Receptor and overcome Resistance Mechanisms

In non-small cell lung cancer (NSCLC), the identification of epidermal growth factor receptor (EGFR) mutations and the parallel development of EGFR tyrosine kinase inhibitors (TKIs) have radically changed the therapeutic management strategies. Currently, erlotinib, gefitinib, and afatinib are all approved as standard first-line treatment in EGFR-mutated NSCLC. However, despite the proven efficacy, some EGFR-mutated NSCLCs do not respond to EGFR TKIs, while some patients, after a favorable and prolonged response to EGFR TKIs, inevitably progress within about 10-14 months. Epidermal growth factor receptor-dependent mechanisms, activation of alternative pathways, or phenotypic transformation can cause the resistance to EGFR TKIs. The exon 20 p.Thr790Met point mutation (T790M) is responsible for about 60% of cases of resistance when progression occurs. A third-generation TKI, osimertinib, improved outcome in patients harboring T790M after first- and second-generation TKI treatment. However, resistance develops even after treatment with third-generation drugs. To date, the Cys797Ser (C797S) mutation in exon 20 of EGFR is the most well-known resistance mutation after osimertinib. Fourth-generation TKIs are already under development. Nevertheless, additional information is needed to better understand and effectively overcome resistance. The aim of this review is to report recent advances and future perspectives in the treatment of EGFR-mutated NSCLC, highlighting the resistance mechanisms that underlie disease progression.

Advances in Circulating Tumor DNA Analysis

The analysis of cell-free circulating tumor DNA (ctDNA) is a very promising tool and might revolutionize cancer care with respect to early detection, identification of minimal residual disease, assessment of treatment response, and monitoring tumor evolution. ctDNA analysis, often referred to as "liquid biopsy" offers what tissue biopsies cannot-a continuous monitoring of tumor-specific changes during the entire course of the disease. Owing to technological improvements, efforts for the establishment of preanalytical and analytical benchmark, and the inclusion of ctDNA analyses in clinical trial, an actual clinical implementation has come within easy reach. In this chapter, recent advances of the analysis of ctDNA are summarized starting from the discovery of cell-free DNA, to methodological approaches and the clinical applicability.

Mechanisms of Resistance to Target Therapies in Non-small Cell Lung Cancer

Targeted therapies are revolutionizing the treatment of advanced non-small cell lung cancer (NSCLC). The discovery of key oncogenic events mainly in lung adenocarcinoma, like EGFR mutations or ALK rearrangements, has changed the treatment landscape while improving the prognosis of lung cancer patients. Inevitably, virtually all patients initially treated with targeted therapies develop resistance because of the emergence of an insensitive cellular population, selected by pharmacologic pressure. Diverse mechanisms of resistance, in particular to EGFR, ALK and ROS1 tyrosine-kinase inhibitors (TKIs), have now been discovered and may be classified in three different groups: (1) alterations in the target (such as EGFR T790M and ALK or ROS1 mutations); (2) activation of alternative pathways (i.e. MET amplification, KRAS mutations); (3) phenotype transformation (to small cell lung cancer, epithelial-mesenchymal transition). These basic mechanisms are informing the development of novel therapeutic strategies to overcome resistance in the clinic. Novel-generation molecules include osimertinib, for EGFR-T790M-positive patients, and new ALK-TKIs. Nevertheless, the possible concomitant presence of multiple resistance mechanisms, as well as their heterogeneity among cells and disease localizations, makes research in this field particularly arduous. In this chapter, available evidence and perspectives concerning precise mechanisms of escape to pharmacological inhibition in oncogene-addicted NSCLC are reported for single targets, including but not limited to EGFR and ALK.

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.

EGFR mutation detection in circulating cell-free DNA of lung adenocarcinoma patients: analysis of LUX-Lung 3 and 6

BACKGROUND

In the Phase III LUX-Lung 3/6 (LL3/LL6) trials in epidermal growth factor receptor (EGFR) mutation-positive lung adenocarcinoma patients, we evaluated feasibility of EGFR mutation detection using circulating cell-free DNA (cfDNA) and prognostic and predictive utility of cfDNA positivity (cfDNA+).

METHODS

Paired tumour and blood samples were prospectively collected from randomised patients. Mutations were detected using cfDNA from serum (LL3) or plasma (LL6) by a validated allele-specific quantitative real-time PCR kit.

RESULTS

EGFR mutation detection rates in cfDNA were 28.6% (serum) and 60.5% (plasma). Mutation detection in blood was associated with advanced disease characteristics, including higher performance score, number of metastatic sites and bone/liver metastases, and poorer prognosis. In patients with common EGFR mutations, afatinib improved progression-free survival vs chemotherapy in cfDNA+ (LL3: HR, 0.35; P=0.0009; LL6: HR, 0.25; P<0.0001) and cfDNA- (LL3: HR, 0.46; P<0.0001; LL6: HR, 0.12; P<0.0001) cohorts. A trend towards overall survival benefit with afatinib was observed in cfDNA+ patients.

CONCLUSIONS

Plasma cfDNA is a promising alternative to biopsy for EGFR testing. Detectable mutation in blood was associated with more advanced disease and poorer prognosis. Afatinib improved outcomes in EGFR mutation-positive patients regardless of blood mutation status.

Molecular pathology in real time

With the development of sophisticated individualized therapeutic approaches, the role of pathology in classification of tumors is enormously increasing. The solely morphological characterization of neoplastic process is no more sufficient for qualified decision on optimal therapeutic approach. Thus, morphologic diagnosis must be supplemented by molecular analysis of the lesion with emphasis on the detection of status of certain markers used as predictive factors for targeted therapy. Both intrinsic and acquired types of intratumor heterogeneity have an impact at various moments of cancer diagnostics and therapy. The primary heterogeneity of neoplastic tissue represents a significant problem in patients, where only limited biopsy samples from the primary tumor are available for diagnosis, such as core needle biopsy specimens in breast cancer, transthoracic or endobronchial biopsies in lung cancer, or endoscopic biopsies in gastric cancer. Detection of predictive markers may be influenced by this heterogeneity, and the marker detection may be falsely negative or (less probably) falsely positive. In addition, as these markers are often detected in the tissue samples from primary tumor, the differences between molecular features of the primary lesion and its metastases may be responsible for failure of systemic therapy in patients with discordant phenotype between primary and metastatic disease. The fact of tumor heterogeneity must be taken into consideration already in establishing pathological diagnosis. One has to be aware that limited biopsy specimen must not always be fully representative of the entire tumor volume. To overcome these limitations, there does not exist one single simple solution. Examination of more tissue (preference of surgical resection specimens over biopsies, whenever possible), use of ultra-sensitive methods able to identify the minute subclones as a source of possible resistance to treatment, and detection of secondary molecular events from the circulating tumor cells or circulating cell-free DNA are potential solutions how to handle this issue.

Transient appearance of circulating tumor DNA associated with de novo treatment

The limitation of circulating tumor DNA (ctDNA) is its inability to detect cancer cell subpopulations with few or no dying cells. Lung cancer patients subjected to the EGFR tyrosine kinase inhibitor (EGFR-TKI) treatment were prospectively collected, and ctDNA levels represented by the activating and T790M mutations were measured. The first data set (21 patients) consisting of samples collected in the period from before initiation of EGFR-TKI to at least 2 weeks after initiation: the ctDNA dynamics generally exhibited a rapid decrease and/or a transient increase. In 4 patients, we detected a transient increase of ctDNA bearing activating mutations not identified in biopsy samples. ctDNA with the same genotypical pattern was identified in 7 out of the 39 patients of the second data set intended to include samples until the onset of disease progression. In 6 of the 7 patients, this unique ctDNA appeared in the early period after treatment initiation, and did not reappear even after disease progression or chemotherapy. In another patient, similar ctDNA appeared upon radiation therapy. The identification of ctDNA with a unique genotype indicates the presence of cancer cell subpopulations that normally contain few or no dying cells, but generate dead cells because of the treatment.

Base-Position Error Rate Analysis of Next-Generation Sequencing Applied to Circulating Tumor DNA in Non-Small Cell Lung Cancer: A Prospective Study

BACKGROUND

Circulating tumor DNA (ctDNA) is an approved noninvasive biomarker to test for the presence of EGFR mutations at diagnosis or recurrence of lung cancer. However, studies evaluating ctDNA as a noninvasive "real-time" biomarker to provide prognostic and predictive information in treatment monitoring have given inconsistent results, mainly due to methodological differences. We have recently validated a next-generation sequencing (NGS) approach to detect ctDNA. Using this new approach, we evaluated the clinical usefulness of ctDNA monitoring in a prospective observational series of patients with non-small cell lung cancer (NSCLC).

METHODS AND FINDINGS

We recruited 124 patients with newly diagnosed advanced NSCLC for ctDNA monitoring. The primary objective was to analyze the prognostic value of baseline ctDNA on overall survival. ctDNA was assessed by ultra-deep targeted NGS using our dedicated variant caller algorithm. Common mutations were validated by digital PCR. Out of the 109 patients with at least one follow-up marker mutation, plasma samples were contributive at baseline (n = 105), at first evaluation (n = 85), and at tumor progression (n = 66). We found that the presence of ctDNA at baseline was an independent marker of poor prognosis, with a median overall survival of 13.6 versus 21.5 mo (adjusted hazard ratio [HR] 1.82, 95% CI 1.01-3.55, p = 0.045) and a median progression-free survival of 4.9 versus 10.4 mo (adjusted HR 2.14, 95% CI 1.30-3.67, p = 0.002). It was also related to the presence of bone and liver metastasis. At first evaluation (E1) after treatment initiation, residual ctDNA was an early predictor of treatment benefit as judged by best radiological response and progression-free survival. Finally, negative ctDNA at E1 was associated with overall survival independently of Response Evaluation Criteria in Solid Tumors (RECIST) (HR 3.27, 95% CI 1.66-6.40, p < 0.001). Study population heterogeneity, over-representation of EGFR-mutated patients, and heterogeneous treatment types might limit the conclusions of this study, which require future validation in independent populations.

CONCLUSIONS

In this study of patients with newly diagnosed NSCLC, we found that ctDNA detection using targeted NGS was associated with poor prognosis. The heterogeneity of lung cancer molecular alterations, particularly at time of progression, impairs the ability of individual gene testing to accurately detect ctDNA in unselected patients. Further investigations are needed to evaluate the clinical impact of earlier evaluation times at 1 or 2 wk. Supporting clinical decisions, such as early treatment switching based on ctDNA positivity at first evaluation, will require dedicated interventional studies.

[Research Advancement on EGFR Mutation Detection of Cell-free DNA and Tumor Cell in Peripheral Blood of Patients with Non-small Cell Lung Cancer]

非小细胞肺癌（non-small cell lung cancer, NSCLC）是肺癌中最常见的类型。表皮生长因子受体（epidermal growth factor receptor, EGFR）酪氨酸激酶受体抑制剂（tyrosine kinases inhibitors, TKIs）是目前最重要的靶向治疗药物，对于有EGFR敏感突变的NSCLC，采用EGFR-TKIs治疗能取得明显的临床疗效；T790M突变是最常见的EGFR-TKIs耐药机制，通过对外周血进行EGFR基因突变检测，可以筛选出EGFR-TKIs治疗有效或治疗过程中对其产生耐药的患者。其定量分析不仅在肿瘤的早期诊断中具有重要意义，而且是疗效评价及随访的重要生物学指标。目前，用于检测外周血EGFR突变的方法有很多，其中以在数字PCR基础上建立起来的ddPCR灵敏度最高，实现了对样本的高通量检测，定量程度较其他方法更为精确，在临床基因诊断中具有广阔的应用前景。

Understanding Mechanisms of Resistance in the Epithelial Growth Factor Receptor in Non-Small Cell Lung Cancer and the Role of Biopsy at Progression

Molecular profiling and the discovery of drugs that target specific activating mutations have allowed the personalization of treatment for non-small cell lung cancer (NSCLC). The epithelial growth factor receptor (EGFR) is frequently over-expressed and/or aberrantly activated in different cancers, including NSCLC. The most common activating mutations of EGFR in NSCLC fall within the tyrosine kinase-binding domain. Three oral EGFR tyrosine kinase inhibitors (TKIs) have been approved by the U.S. Food and Drug Administration (FDA) for first-line use in patients with EGFR mutation-positive NSCLC (exon 19 deletions or exon 21 [L858R] substitution mutations), as detected by an FDA-approved test. However, disease progression is common and is often the result of secondary mutations, of which the EGFR T790M mutation is the most prevalent. Few options were available upon progression until the introduction of osimertinib, a kinase inhibitor that targets the T790M mutation, which was recently approved for use in patients with metastatic EGFR T790M mutation-positive NSCLC, as detected by an FDA-approved test, who progressed on or after EGFR TKI therapy. With the introduction of osimertinib, outcomes can now be improved in select patients. Therefore, performing a biopsy at progression to determine the underlying molecular cause of the acquired resistance is important for the enabling of individualized options that may provide the greatest opportunity for improved outcomes. This review discusses the latest updates in molecular testing at progression and outlines treatment options for this difficult-to-treat population.

THE ONCOLOGIST

2017;22:3-11 IMPLICATIONS FOR PRACTICE: Although the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs)-gefitinib, erlotinib, and afatinib-have changed the treatment paradigm for non-small cell lung cancer among those with EGFR mutation positive disease, most patients experience progression after approximately 12 months of treatment. Until recently, options were limited for patients who progressed, but improvements in molecular profiling and the approval of osimertinib, which targets the resistance mutation T790M, afford the opportunity for improved outcomes in many patients with this mutation. This article explains the options available after progression on initial EGFR TKI therapy and the importance of molecular testing at progression in making treatment decisions.

Three-color crystal digital PCR

Digital PCR is an exciting new field for molecular analysis, allowing unprecedented precision in the quantification of nucleic acids, as well as the fine discrimination of rare molecular events in complex samples. We here present a novel technology for digital PCR, Crystal Digital PCR™, which relies on the use of a single chip to partition samples into 2D droplet arrays, which are then subjected to thermal cycling and finally read using a three-color fluorescence scanning device. This novel technology thus allows three-color multiplexing, which entails a different approach to data analysis. In the present publication, we present this innovative workflow, which is both fast and user-friendly, and discuss associated data analysis issue, such as fluorescence spillover compensation and data representation. Lastly, we also present proof-of-concept of this three-color detection system, using a quadriplex assay for the detection of EGFR mutations L858R, L861Q and T790M.

Analysis of Base-Position Error Rate of Next-Generation Sequencing to Detect Tumor Mutations in Circulating DNA

BACKGROUND

Detecting single-nucleotide variations and insertions/deletions in circulating tumor DNA is challenging because of their low allele frequency. The clinical use of circulating tumor DNA to characterize tumor genetic alterations requires new methods based on next-generation sequencing.

METHODS

We developed a method based on quantification of error rate of each base position [position error rate (PER)]. To identify mutations, a binomial test was used to compare the minor-allele frequency to the measured PER at each base position. This process was validated in control samples and in 373 plasma samples from patients with lung or pancreatic cancer.

RESULTS

Minimal mutated allele frequencies were 0.003 for single-nucleotide variations and 0.001 for insertions/deletions. Independent testing performed by droplet digital PCR (n = 231 plasma samples) showed strong agreement with the base-PER method (κ = 0.90).

CONCLUSIONS

Targeted next-generation sequencing analyzed with the base-PER method represents a robust and low cost method to detect circulating tumor DNA in patients with cancer.

EGFR as a Pharmacological Target in EGFR-Mutant Non-Small-Cell Lung Cancer: Where Do We Stand Now?

Targeting the epidermal growth factor receptor (EGFR) using tyrosine kinase inhibitors (TKIs) is highly effective in terms of tumor response rate, survival, and quality of life. However, acquired resistance to EGFR-TKIs is inevitable. Ongoing clinical trials will provide evidence for optimal strategies for patients with EGFR mutant non-small-cell lung cancer (NSCLC) in the near future. Numerous new agents are specifically addressing resistance mechanisms; mature data are related to the T790M mutation and MET pathway activation. Here, we provide a comprehensive review of new perspectives on how to optimize the management of this molecular disease.

Noninvasive genotyping and monitoring of anaplastic lymphoma kinase (ALK) rearranged non-small cell lung cancer by capture-based next-generation sequencing

Noninvasive genotyping of driver genes and monitoring of tumor dynamics help make better personalized therapeutic decisions. However, neither PCR-based assays nor amplicon-based targeted sequencing can detect fusion genes like anaplastic lymphoma kinase (ALK) rearrangements in blood samples. To investigate the feasibility and performance of capture-based sequencing on ALK fusion detection, we developed a capture-based targeted sequencing panel to detect and quantify rearrangement events, along with other driver mutation variants in plasma. In this perspective study, we screened 364 patients with advanced non-small cell lung cancer (NSCLC) for ALK rearrangements, and collected blood samples from 24 of them with confirmed ALK rearrangements based on their tissue biopsies. ALK rearrangements were successfully detected in 19 of 24 patients at baseline with 79.2% (95% CI 57.9%, 92.9%) sensitivity and 100% (36/36) specificity. Among the 24 patients, we obtained longitudinal blood samples from 7 of them after either chemotherapy and/or Crizotinib treatment for disease monitoring. The by-sample detection rate of ALK rearrangements after treatment drops to 69.2% (9 of 13). In addition to detecting ALK rearrangements, we also detected 3 Crizotinib resistant mutations, ALK L1152R, ALK I1171T and ALK L1196M from patient P4. ctDNA concentration correlates with responses and disease progression, reflecting its ability as a biomarker. Our findings suggest capture-based sequencing can detect and quantify ALK rearrangements as well as other somatic mutations, including mutations mediated drug resistance, in plasma with high sensitivity, paving the way for its application in identifying driver fusion genes and monitoring tumor dynamics in the clinic.

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.

KRAS mutations in the circulating free DNA (cfDNA) of non-small cell lung cancer (NSCLC) patients

Circulating free DNA (cfDNA) is obtained from serum or plasma by non-invasive methods such as a simple blood draw, a technique known as "liquid biopsy". Genetic analyses of driver alterations in cfDNA have proved very effective to predict survival and treatment response of cancer patients according to tumoral cfDNA burden in blood. Non-small cell lung cancer (NSCLC) patients with higher concentration of tumoral cfDNA in blood have, on average, shorter progression-free survival (PFS) and overall survival (OS). Regarding specific genetic alterations, KRAS proto-oncogene, GTPase (KRAS) is one of the main genes involved in NSCLC and several studies have been performed to determine its value as a predictive and prognostic biomarker in liquid biopsy. Unfortunately, to date no strong conclusions can be drawn since they have yielded contradictory results. Therefore, further investigations are necessary to establish the value of KRAS testing in liquid biopsy as prognostic or predictive factor in NSCLC. Herein, we review the current knowledge on the importance of KRAS as prognostic and predictive biomarker using non-invasive approaches and the scientific data available regarding its application in clinical practice for treatment of NSCLC.

Circulating tumor DNA detection in lung cancer patients before and after surgery

Circulating tumor DNA (ctDNA) in peripheral blood is a "liquid biopsy" that contains representative tumor information including gene mutations. Additionally, repeated ctDNA samples can be easily obtained to monitor response to treatment and disease progression, which may be especially valuable to lung cancer patients with tumors that cannot be easily biopsied or removed. To investigate the changes in ctDNA after surgical tumor resection, tumor and blood samples obtained before and after surgery were collected prospectively from 41 non-small lung cancer (NSCLC) patients. Somatic driver mutations in tumor DNA (tDNA) and pre- and post-op plasma ctDNA sample pairs were identified by targeted sequencing in several genes including EGFR, KRAS, and TP53 with an overall study concordance of 78.1% and sensitivity and specificity of 69.2% and 93.3%, respectively. Importantly, the frequency of 91.7% of ctDNA mutations decreased after surgery and these changes were observed as little as 2 days post-op. Moreover, the presence of ctDNA had a higher positive predictive value than that of six tumor biomarkers in current clinical use. This study demonstrates the use of targeted sequencing to reliably identify ctDNA changes in response to treatment, indicating a potential utility of this approach in the clinical management of NSCLC.

Early Prediction of Response to Tyrosine Kinase Inhibitors by Quantification of EGFR Mutations in Plasma of NSCLC Patients

INTRODUCTION

The potential to accurately quantify epidermal growth factor receptor (EGFR) mutations in plasma from non-small-cell lung cancer patients would enable more rapid and more frequent analyses to assess disease status; however, the utility of such analyses for clinical purposes has only recently started to explore.

METHODS

Plasma samples were obtained from 69 patients with EGFR-mutated tumors and 21 negative control cases. EGFR mutations in plasma were analyzed by a standardized allele-specific polymerase chain reaction (PCR) test and ultra-deep next-generation sequencing (NGS). A semiquantitative index (SQI) was derived from dilutions of known EGFR mutation copy numbers. Clinical responses were evaluated by Response Evaluation Criteria in Solid Tumors 1.1 criteria and expressed as percent tumor shrinkage.

RESULTS

The sensitivity and specificity of the PCR test and NGS assay in plasma versus tissue were 72% versus 100% and 74% versus 100%, respectively. Quantitative indices by the PCR test and NGS were significantly correlated (p < 0.001). EGFR testing at baseline and serially at 4 to 60 days during tyrosine kinase inhibitor therapy revealed a progressive decrease in SQI, starting from day 4, in 95% of cases. The rate of SQI decrease correlated with percent tumor shrinkage at 2 months (p < 0.0001); at 14 days, it was more than 50% in 70% of patients (rapid responders). In two patients with slow response, an early increase in the circulating levels of the T790M mutation was observed. No early T790M mutations were seen in plasma samples of rapid responders.

CONCLUSIONS

Quantification of EGFR mutations from plasma with a standardized PCR test is feasible. To our knowledge, this is the first study showing a strong correlation between the EGFR SQI in the first days of treatment and clinical response with relevant implications for patient management.