Circulating Plasma DNA Research Articles

23. Detection of somatic tumor mutations in circulating plasma DNA of patients with sellar and skull base tumors

23. Detection of somatic tumor mutations in circulating plasma DNA of patients with sellar and skull base tumors

Analysis of Septin 9 Gene Hypermethylation as Follow-Up Biomarker of Colorectal Cancer Patients after Curative Surgery.

Background: The Septin 9 test analyzes the methylation status of the SEPT9 gene, which appears to be hypermethylated in patients with colorectal cancer (CRC). This has been validated as a colorectal cancer screening test. Due to the high sensitivity and specificity found, the justification was to use it as a biomarker tool for monitoring minimal residual disease after radical surgery and recurrence. Methods: A prospective study was carried out at the Fundación Jiménez Díaz University Hospital extracting peripheral blood from 28 patients and 4 healthy donors. Free circulating DNA was obtained and subsequently a PCR reaction to quantify the number of methylated genes. Samples were obtained preoperatively and postoperatively at five to seven days, one and three months after surgery. Results: A total of 32 preoperative samples were analyzed. The sensitivity of the test to detect CRC was 55.6% and specificity was 100%. There were 22 postsurgical samples obtained at 5–7 days after surgery, the sensitivity to detect tumor recurrences was 100% and specificity was 75%. There were 21 samples analyzed 1 month after surgery exhibiting a sensitivity and specificity of 100% and 94.7%, respectively. At 3 months, 31 postsurgical samples were analyzed and the sensitivity and specificity were 66.7% and 80%. Conclusions: Detection of methylation of Septin 9 gene in circulating plasma DNA, obtained from a peripheral blood sample, may be a useful, non-invasive and effective method for detecting minimal residual disease and could therefore predict CRC tumor recurrences. The optimal time in our series to obtain the best prediction results based on Septin 9 methylation levels was one month after surgery. Despite these considerable findings, a study with more patients is necessary to obtain more robust conclusions.

Ultra-Deep Sequencing of Plasma-Circulating DNA for the Detection of Tumor- Derived Mutations in Patients with Nonmetastatic Colorectal Cancer

Identification of tumor-derived mutation (TDM) in liquid biopsies (LB), especially in early-stage patients, faces several challenges, including low variant-allele frequencies, interference by white blood cell (WBC)-derived mutations (WDM), benign somatic mutations and tumor heterogeneity. Here, we addressed the above-mentioned challenges in a cohort of 50 nonmetastatic colorectal cancer patients, via a workflow involving parallel sequencing of paired WBC- and tumor-gDNA. After excluding potential false positive mutations, we detected at least one TDM in LB of 56% (28/50) of patients, with the majority showing low-patient coverage, except for one TDM mapped to KMT2D that recurred in 30% (15/30) of patients.

Cell-Free Circulating Plasma DNA in Prostate Cancer

Cell-Free Circulating Plasma DNA in Prostate Cancer

High-accuracy liquid biopsies.

Ultra-deep sequencing of paired plasma-circulating free DNA and white blood cells allows the identification of tumor-derived somatic mutations with high accuracy by filtering out variants consistent with clonal hematopoiesis.

Detection of incipient tumours by screening of circulating plasma DNA: hype or hope?

ABSTRACTBackground: The last half-decade has been marked by a rapid expansion of research efforts in the field of so-called liquid biopsies, thereby investigating the potential of blood-derived cell-free tumour DNA (ctDNA) markers for application in clinical oncological management. The analysis of cfDNA appears to be particularly attractive for therapy monitoring purposes, while in terms of early cancer diagnosis and screening the potentials are just starting to be explored. Challenges, both of biological and technical nature, need to be addressed. One such challenge is to overcome the low levels of ctDNA in the circulation, intrinsic to many early-stage cancers. Methods: Here, we give an overview of the features of ctDNA and the approaches that are currently being applied with the ultimate aim to detect tumours in a presymptomatic stage. Conclusion: Although many studies report encouraging results, further technical development and larger studies are warranted before application of ctDNA analysis may find its place in clinic.

Abstract 2213: Investigation of treatment resistance with DNA-damage agents in patients with triple negative breast cancer by ctDNA

Abstract Loss of function (LOF) germline mutation in BRCA1 increases the risk of breast cancer, especially the triple-negative breast cancer (TNBC) subtype, a very aggressive tumor. TNBC exhibits high variability at both molecular and clinical aspects. BRCA impairment is associated to deficiency in homologous recombination repair (HRD) and tumor with HRD has benefit from treatment with drugs that induces DNA damage and also with PARP inhibitor. We previously detected that a significant fraction of TNBC diagnosed in young Brazilian exhibits BRCA1 impairment by both mechanisms - germline pathogenic mutation and promoter hypermethylation - and that this group of tumor presented better overall survival (Brianese et al 2018). In the current study our aim is to comprehensively characterize the resistance to DNA-damage agents in patients with TNBC associated or not with HRD by investigating somatic mutations in circulating plasma DNA (cDNA). Thus, are also investigating 6 serial cDNA samples of patients during neoadjuvant and adjuvant chemotherapy treatment. Patients are subjected to genetic testing using a 26-gene panel including the homologous recombination (HR) predisposing genes for classifying the TNBC in hereditary or sporadic. The somatic mutations identified in the tumor biopsy by using a gene panel containing frequently mutated genes in breast tumor cancer have been screened in serial plasma samples to check allele frequency of the somatic mutation in circulating DNA and to correlate to therapy response. Results: We have enrolled 32 TNBC patients of which 28 were tested by germline variants. Based on 18 samples we had 50% of pathological complete response. Pathogenic mutations were identified only in BRCA1 in 5 out of 28 (17.8%) patients. Additionally, variants of uncertain significance (VUS) were identified in 18 out of the 26 genes (64.2% - 18/28) patients, being ATM the most affected gene by VUS. In terms of somatic variants, tumor mutation burden (TMB) analysis showed that 25% has high and 75% low TMB, with no association with BRCA1 germline status. Also, we found an average three somatic variants per tumor (range 1-7) and used as tumor marks in the screening of circulating DNA in plasma (cDNA). Somatic mutations in TP53 were identified in all tumor biopsy samples. In cDNA in plasma before treatment, confident detection of at least one tumor mutation was observed in 6 out of 8 patients (75%), including somatic mutations in TP53 and SAMD9 genes. Serial plasma cDNA samples were completely investigated for two patients until now and the results showed great association with the clinical response data suggesting that the chemotherapy-resistance mechanisms can be investigated by ctDNA in TNBC. Supported by FAPESP, CNPq and Capes. Citation Format: Rafael R. Brianese, Giovana T. Torrezan, Marina De Brot, Maria Nirvana Formiga, Vladmir de Lima, Fabiana B. Makdissi, Dirce Maria Carraro. Investigation of treatment resistance with DNA-damage agents in patients with triple negative breast cancer by ctDNA [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2213.

Activity of osimetrinib/AZD9291 in pretreated patients (pts) with epidermal growth factor receptor mutant (EGFRmt) non-small cell lung cancer (NSCLC), according to EGFR mutations detected in circulating plasma DNA (ctDNA).

e20608 Background: Osimertinib is an irreversible EGFR tyrosine kinase inhibitor (TKI), selective for EGFR TKI-sensitizing mutations and the T790M resistance mutation. We sought to determine the activity of osimertinib after progression on EGFR TKIs in pts with T790-negative ctDNA. Methods: A multicenter phase II study ( clinicaltrials.gov NCT02771314) of osimertinib (80 mg daily) was conducted in pts with metastatic EGFRmt NSCLC, who had progressed after previous treatment with EGFR TKIs. Serial serum and/or plasma samples were drawn for ctDNA analysis at enrollment, 1 month and every 3 months of treatment, until disease progression. Efficacy outcomes in pts without the T790M mutation in ctDNA at baseline are reported. Results: Thirty-seven NSCLC patients with undetectable baseline T790M in the plasma have been enrolled. Median age was 67 years, 21.6% were male, and histology was adenocarcinoma in 100%. More frequent adverse events (grade 1/2) included diarrhea (12.5%), fatigue (12.5%), anorexia (12.5%) and acneiform rash (10.4%). The overall response rate (ORR) was 40.5% (95% CI, 24.7-56.4%) and the disease stabilization rate 37.8%; the median progression-free survival (PFS) was 8.9 months (range, 1.6-30), and the estimated median overall survival (OS) 26 months (range, 2.2-30). At enrollment, EGFR mutations del19 and L858R were detected in ctDNA in 9 and 3 pts, respectively. After one month of treatment with osimertinib, EGFR mutations in ctDNA were not detectable in 4/9 and 2/3 of pts with del19 and L858R at baseline, respectively. Pts without detectable EGFRm ctDNA at baseline remained negative throughout the study. Efficacy according to baseline ctDNA status was as follows: Clinical trial information: NCT02771314. Conclusions: Osimertinib was effective in EGFR TKI pretreated pts without EGFR T790M mutation in plasma. Pts with detectable del19 or L858R mutations in ctDNA before treatment had worse clinical outcomes, despite the elimination of EGFRmt ctDNA.[Table: see text]

Tu1165 – Circulating Plasma Dna Methylation Status of Tumor Suppressor Genes May Be a Predictive Factor of Lung Metastasis in Colorectal Cancer

Tu1165 – Circulating Plasma Dna Methylation Status of Tumor Suppressor Genes May Be a Predictive Factor of Lung Metastasis in Colorectal Cancer

Genomewide copy number alteration screening of circulating plasma DNA: potential for the detection of incipient tumors.

Early cancer diagnosis might improve survival rates. As circulating tumor DNA (ctDNA) carries cancer-specific modifications, it has great potential as a noninvasive biomarker for detection of incipient tumors. We collected cell-free DNA (cfDNA) samples of 1002 elderly without a prior malignancy, carried out whole-genome massive parallel sequencing and scrutinized the mapped sequences for the presence of (sub)chromosomal copy number alterations (CNAs) predictive for a malignancy. When imbalances were detected, 6-monthly clinical follow-up was carried out. In 3% of participants chromosomal imbalances were detected. Follow-up analyses, including whole-body MRI screening, confirmed the presence of five hematologic malignancies: one Hodgkin lymphoma (HL), stage II; three non-HL (type chronic lymphocytic leukemia, Rai I-Binet A; type SLL, stage III; type mucosa-associated lymphoid tissue, stage I) and one myelodysplastic syndrome with excess blasts, stage II. The CNAs detected in cfDNA were tumor-specific. Furthermore, one case was identified with monoclonal B-cell lymphocytosis, a potential precursor of B-cell malignancy. In 24 additional individuals, CNAs were identified but no cancer diagnosis was made. For 9 of them, the aberrant cfDNA profile originated from peripheral blood cells. For 15 others the origin of aberrations in cfDNA remains undetermined. Genomewide profiling of cfDNA in apparently healthy individuals enables the detection of incipient hematologic malignancies as well as clonal mosaicism with unknown clinical significance. CNA screening of cellular DNA of peripheral blood in elderly has established that clonal mosaicism for these chromosomal anomalies predicts a 5- to 10-fold enhanced risk of a subsequent cancer. We demonstrate that cfDNA screening detects CNAs, which are not only derived from peripheral blood, but even more from other tissues. Since the clinical relevance of clonal mosaics in other tissues remains unknown, long-term follow-up is warranted. Taken together, this study demonstrates that genomewide cfDNA analysis has potential as an unbiased screening approach for hematological malignancies and premalignant conditions.

Dnase1l3 deletion causes aberrations in length and end-motif frequencies in plasma DNA

Circulating DNA in plasma consists of short DNA fragments. The biological processes generating such fragments are not well understood. DNASE1L3 is a secreted DNASE1-like nuclease capable of digesting DNA in chromatin, and its absence causes anti-DNA responses and autoimmunity in humans and mice. We found that the deletion of Dnase1l3 in mice resulted in aberrations in the fragmentation of plasma DNA. Such aberrations included an increase in short DNA molecules below 120 bp, which was positively correlated with anti-DNA antibody levels. We also observed an increase in long, multinucleosomal DNA molecules and decreased frequencies of the most common end motifs found in plasma DNA. These aberrations were independent of anti-DNA response, suggesting that they represented a primary effect of DNASE1L3 loss. Pregnant Dnase1l3-/- mice carrying Dnase1l3+/- fetuses showed a partial restoration of normal frequencies of plasma DNA end motifs, suggesting that DNASE1L3 from Dnase1l3-proficient fetuses could enter maternal systemic circulation and affect both fetal and maternal DNA fragmentation in a systemic as well as local manner. However, the observed shortening of circulating fetal DNA relative to maternal DNA was not affected by the deletion of Dnase1l3 Collectively, our findings demonstrate that DNASE1L3 plays a role in circulating plasma DNA homeostasis by enhancing fragmentation and influencing end-motif frequencies. These results support a distinct role of DNASE1L3 as a regulator of the physical form and availability of cell-free DNA and may have important implications for the mechanism whereby this enzyme prevents autoimmunity.

A14264 Circulating Plasma DNA as Potential Markers for Pregnancy Associated Metabolic Complications

Objectives: To assess circulating plasma DNA (pDNA) as a possible predictive factor for pregnancy associated metabolic complications. Methods: Blood samples were collected from 200 subjects, in the second trimester of pregnancy from Obstetrics and Gynecology Clinic, KGMU, Lucknow, India. pDNA from all samples was quantified spectrophotometrically and in real-time quantitative PCR (qPCR), using β-actin and GAPDH housekeeping gene primers. Statistics was applied using SPSS (ver. 21.0). Results: The qPCR analysis for β-actin and GAPDH at II trimester of pregnancy demonstrated a significant increase (P = 0.001) in concentration of pDNA in pre-eclamptic cases as compared with normal healthy pregnant subjects. Similarly, significant increase (P = 0.003 and 0.002) was observed in gestational diabetes (GDM) cases for β-actin and GAPDH gene primers respectively. Conclusion: Our results confirmed that concentrations of circulating plasma DNA may be used as a possible early predictive marker for pregnancy associated metabolic complications.

1336O - Unbiased genomewide screening of circulating plasma DNA for cancer detection

1336O - Unbiased genomewide screening of circulating plasma DNA for cancer detection

Evaluation of cell free circulating plasma DNA in prostate cancer

Background: Prostate cancer (PC) is the most common cancer affecting men, it accounts for 29% of all male cancer and 11% of all male cancer related deaths. DNA is normally released from an apoptotic source which generates small fragments of cell-free DNA, whereas cancer patients have cell-free circulating DNA that originated from necrosis, autophagy, or mitotic catastrophe, which produce large fragments. Aim of work: Differentiate the cell free DNA levels (CFDNA) and its integrity in prostate cancer patients and control group composed of benign prostate hyperplasia (BPH) and healthy persons. Methodology: cf-DNA levels were quantified by real-time PCR amplification in prostate cancer patients (n = 50), (BPH) benign prostate hyperplasia (n = 25) and healthy controls (n = 30) using two sets of ALU gene (product size of 115 bp and 247-bp) and its integrity was calculated as a ratio of qPCR results of 247 bp ALU over 115 bp ALU. Results: Highly significant levels of cf-DNA and its integrity in PC patients compared to BPH. Twenty-eight (56%) patients with prostate cancer had bone metastasis. ALU115 q PCR is superior to the other markers in discriminating metastatic patients with a sensitivity of 96.4% and a specificity of 86.4% (AUC = 0.981) Conclusion: ALU115 q PCR could be used as a valuable biomarker helping in identifying high risk patients, indicating early spread of tumor cells as a potential seed for future metastases.

Enhanced detection of microsatellite instability using pre-PCR elimination of wild-type DNA homo-polymers in tissue and liquid biopsies.

Detection of microsatellite-instability in colonoscopy-obtained polyps, as well as in plasma-circulating DNA, is frequently confounded by sensitivity issues due to co-existing excessive amounts of wild-type DNA. While also an issue for point mutations, this is particularly problematic for microsatellite changes, due to the high false-positive artifacts generated by polymerase slippage (stutter-bands). Here, we describe a nuclease-based approach, NaME-PrO, that uses overlapping oligonucleotides to eliminate unaltered micro-satellites at the genomic DNA level, prior to PCR. By appropriate design of the overlapping oligonucleotides, NaME-PrO eliminates WT alleles in long single-base homopolymers ranging from 10 to 27 nucleotides in length, while sparing targets containing variable-length indels at any position within the homopolymer. We evaluated 5 MSI targets individually or simultaneously, NR27, NR21, NR24, BAT25 and BAT26 using DNA from cell-lines, biopsies and circulating-DNA from colorectal cancer patients. NaME-PrO enriched altered microsatellites and detected alterations down to 0.01% allelic-frequency using high-resolution-melting, improving detection sensitivity by 500–1000-fold relative to current HRM approaches. Capillary-electrophoresis also demonstrated enhanced sensitivity and enrichment of indels 1–16 bases long. We anticipate application of this highly-multiplex-able method either with standard 5-plex reactions in conjunction with HRM/capillary electrophoresis or massively-parallel-sequencing-based detection of MSI on numerous targets for sensitive MSI-detection.

Prognostic value of various subtypes of circulating DNA in ovarian cancer patients.

e17092 Background: Patients with ovarian cancer represent a heterogeneous population with a variable prognosis and response to chemotherapy. Circulating tumor DNA has been shown to have a prognostic value in different types of cancer including ovarian carcinoma. Whether total circulating DNA, which can be assessed much easier without knowing the tumor-specific mutations, has similar informative value is currently unknown. The aim of this study was to evaluate the prognostic value of circulating DNA in advanced ovarian cancer. Methods: This prospective study included 67 patients (pts) with ovarian cancer treated with 1st line paclitaxel and carboplatin (25 pts) and bevacizumab (42 pts). Thirty-five patients had optimal debulking before chemotherapy. Circulating plasma DNA was quantified using real time PCR before administration of chemotherapy (67 pts) and after 6 cycles of chemotherapy (44 pts). Results: Total extracellular DNA (ecDNA), as well as extracellular DNA of nuclear (nDNA) and mitochondrial origin (mtDNA) significantly (p < 0.05) decreased after 6 cycles of chemotherapy (by 54%, 63% and 52%, respectively. Patients with stage I disease had significantly lower mtDNA compared to patients with stage II-IV (8604 vs. 16984 ge/mL, p = 0.03). Patients with lower baseline nDNA had superior progression-free (HR=0.35 (0.14-0.86)) and overall survival (HR=0.18 (0.04-0.77). The prognostic value of nDNA was confirmed independent of tumor stage and confirmed in multivariate analysis. Conclusions: Our data suggest that ecDNA of both, nuclear and mitochondrial origin, could be added to prognostic markers in ovarian cancer. This is of importance as this analysis does not require the knowledge of tumor-specific mutations in contrast to the quantification of tumor-derived ecDNA. Analysis of the dynamics and cell type-specific source of the ecDNA could shed light on its biology in cancer and might help to direct the treatment of ovarian cancer.

Evaluation of clinical outcomes by analysis of mutations in tumor tissue and circulating plasma DNA using next-generation sequencing (NGS) from STEAM, a prospective, randomized, multicenter study in metastatic colorectal cancer (mCRC).

11510 Background: STEAM (NCT01765582) assessed the efficacy and safety of concurrent (c) and sequential (s) FOLFOXIRI-bevacizumab (BEV) vs FOLFOX-BEV for first-line treatment of mCRC. Methods: The AVENIO ctDNA Expanded Kit (Research Use Only) was used to assess somatic mutations in 77 cancer-related genes by NGS in tissue, and both pre- and post-induction plasma samples (n = 182, 150 and 118 respectively) from STEAM. Four mutation classes including single-nucleotide variants (SNVs), indels, copy number amplifications (CNAs) and fusions were identified. SNVs and indels were called in tissue and plasma at allele frequencies of 5% and 0.25% respectively. Results: Overall concordance of mutations in pre-induction plasma with tissue was 83%. Concordance for the seven most mutated genes ranged from 91.5%-100%. In pts with matched samples (n = 118), RAS WT pts showed significantly longer progression-free survival (PFS) in both cFOLFOXIRI-BEV (A) and sFOLFOXIRI-BEV (B) arms versus FOLFOX-BEV (C), using genotyping of either tissue or plasma. This was not seen in RAS MUT pts. In contrast, TP53 WT showed no significant treatment differences while TP53 MUT showed longer PFS for cFOLFOXIRI-BEV versus FOLFOX-BEV. A list of mutation frequencies for all samples, as well as hierarchical clustering analysis of tissue mutations will be presented. Conclusions: The AVENIO ctDNA Expanded Kit identified mutations in 77 cancer-related genes, in both plasma and tissue, with high overall concordance. Compared to FOLFOX-BEV, longer PFS was observed for c- or s- FOLFOXIRI-BEV in RAS WT pts and for cFOLFOXIRI-BEV in TP53 MUT pts, irrespective of sample type. These results are hypothesis generating and require further clinical validation. Clinical trial information: NCT01765582. [Table: see text]

Methylation-sensitive enrichment of minor DNA alleles using a double-strand DNA-specific nuclease.

Aberrant methylation changes, often present in a minor allelic fraction in clinical samples such as plasma-circulating DNA (cfDNA), are potentially powerful prognostic and predictive biomarkers in human disease including cancer. We report on a novel, highly-multiplexed approach to facilitate analysis of clinically useful methylation changes in minor DNA populations. Methylation Specific Nuclease-assisted Minor-allele Enrichment (MS-NaME) employs a double-strand-specific DNA nuclease (DSN) to remove excess DNA with normal methylation patterns. The technique utilizes oligonucleotide-probes that direct DSN activity to multiple targets in bisulfite-treated DNA, simultaneously. Oligonucleotide probes targeting unmethylated sequences generate local double stranded regions resulting to digestion of unmethylated targets, and leaving methylated targets intact; and vice versa. Subsequent amplification of the targeted regions results in enrichment of the targeted methylated or unmethylated minority-epigenetic-alleles. We validate MS-NaME by demonstrating enrichment of RARb2, ATM, MGMT and GSTP1 promoters in multiplexed MS-NaME reactions (177-plex) using dilutions of methylated/unmethylated DNA and in DNA from clinical lung cancer samples and matched normal tissue. MS-NaME is a highly scalable single-step approach performed at the genomic DNA level in solution that combines with most downstream detection technologies including Sanger sequencing, methylation-sensitive-high-resolution melting (MS-HRM) and methylation-specific-Taqman-based-digital-PCR (digital Methylight) to boost detection of low-level aberrant methylation-changes.

Detection of KRAS Mutations in Circulating Tumor DNA by Digital PCR in Early Stages of Pancreatic Cancer.

Since surgical removal remains the only cure for pancreatic cancer, early detection is of utmost importance. Circulating biomarkers have potential as diagnostic tool for pancreatic cancer, which typically causes clinical symptoms only in advanced stage. Because of their high prevalence in pancreatic cancer, KRAS proto-oncogene, GTPase [KRAS (previous name: Kirsten rat sarcoma viral oncogene homolog)] mutations may be used to identify tumor-derived circulating plasma DNA. Here we tested the diagnostic sensitivity of chip based digital PCR for the detection of KRAS mutations in circulating tumor DNA (ctDNA) in early stage pancreatic cancer. We analyzed matched plasma (2 mL) and tumor samples from 50 patients with pancreatic cancer. Early stages (I and II) were predominant (41/50) in this cohort. DNA was extracted from tumor and plasma samples and tested for the common codon 12 mutations G12D, G12V, and G12C by chip-based digital PCR. We identified KRAS mutations in 72% of the tumors. 44% of the tumors were positive for G12D, 20% for G12V, and 10% for G12C. One tumor was positive for G12D and G12V. Analysis of the mutations in matched plasma samples revealed detection rates of 36% for G12D, 50% for G12V, and 0% for G12C. The detection appeared to be correlated with total number of tumor cells in the primary tumor. No KRAS mutations were detected in 20 samples of healthy control plasma. Our results support further evaluation of tumor specific mutations as early diagnostic biomarkers using plasma samples as liquid biopsy.

Mutation analysis of circulating plasma DNA to determine response to EGFR tyrosine kinase inhibitor therapy of lung adenocarcinoma patients.

Long-lasting success in lung cancer therapy using tyrosine kinase inhibitors (TKIs) is rare since the tumors develop resistance due to the occurrence of molecularly altered subclones. The aim of this study was to monitor tumors over time based on the quantity of mutant plasma DNA and to identify early indications for therapy response and tumor progression. Serial plasma samples from lung adenocarcinoma patients treated with TKIs were used to quantify EGFR and KRAS mutations in circulating DNA by digital PCR. Mutant DNA levels were compared with the courses of responses to treatment with TKIs, conventional chemotherapy, radiotherapy, or combinations thereof. Variations in plasma DNA mutation levels over time were found in 15 patients. We categorize three major courses: First, signs of therapy response are associated with a fast clearing of plasma DNA mutations within a few days. Second, periods of stable disease are accompanied by either absence of mutations or fluctuation at low levels. Finally, dramatic increase of mutational load is followed by rapid tumor progression and poor patient survival. In summary, the serial assessment of EGFR mutations in the plasma of NSCLC patients allows conclusions about controlled disease and tumor progression earlier than currently available methods.