Genotyping cell-free tumor DNA in the blood to detect residual disease and drug resistance
© Siravegna and Bardelli; licensee BioMed Central 2014
Published: 30 August 2014
DNA fragments released from cancer cells into the blood can be used to generate molecular profiles of tumors. Non-invasive 'liquid biopsies' can be used to monitor minimal residual disease and detect the emergence of drug resistance.
Precision oncology relies on the availability of accurate molecular profiles of individual tumors, which are currently determined by genetic analysis of DNA extracted from neoplastic tissue. Sampling tumor tissue from surgical specimens or biopsies has significant limitations. Biopsies provide a single snapshot in time, are subject to selection bias resulting from tumor heterogeneity, can lead to severe clinical complications and can be difficult to obtain -. Tumor cells release DNA into the blood, and this offers the opportunity to determine the genetic landscapes of solid cancer from the circulation, an approach commonly called 'liquid biopsy'. Here, we summarize applications of liquid biopsies to interrogate cancer genomics in the blood of patients in different clinical scenarios.
Liquid biopsies, an evolving concept
Significantly higher cfDNA concentrations are present in serum than in plasma -. The increased level of cfDNA in serum is due to the clotting of white blood cells in the collection tube, leading to their lysis ,,. As a consequence, cfDNA in serum is 'diluted' by genomic DNA released from white blood cells. Accordingly, plasma is a better source of specific tumor cfDNA ,.
In general, concentrations of cfNAs are higher in individuals with cancer than in healthy controls, and levels are further increased in metastasis. Both tumor-derived and normal germline cfNAs are released into the blood, and the proportion of tumor-derived cfNA is broadly related to the extent of the disease . The amount of cfNA is also influenced by clearance, degradation and other physiological filtering events in the blood and lymphatic circulation -. Nucleic acids are cleared from the blood by the liver and kidneys and have a variable half-life in the circulation, ranging from 15 minutes to several hours . The release of nucleic acids into the blood is not fully understood but is probably related to the fast turnover of cancer cells and the ensuing apoptosis or necrosis ,. Numerous studies show that virtually all living cells actively release DNA fragments . The presence of DNA and RNA in exosomes, vesicles that are actively released by multiple cell types (including neoplastic cells), is also well documented -.
It has been estimated that a tumor that weighs 100 g (which corresponds to 3 × 1010 cancer cells), may release up to 3.3% of the DNA present in the cancer cells into the blood every day . The size of tumor cfDNAs detected in the blood of cancer patients is highly variable: most are 70 to 200 base pairs long but fragments of up to 21 kilobases have also been detected . In patients, the amount of cfDNA ranges between 0 and >1,000 ng/ml of blood, with an average of 180 ng/ml -. Monitoring cfDNA concentrations per se does not seem to be useful for diagnostic purpose because several physiological and pathological conditions besides cancer can lead to great changes in cfDNA levels. For instance, pro-inflammatory diseases, such as liver cirrhosis, hepatitis, systemic lupus erythematous or rheumatoid arthritis ,, all lead to the release of high levels of cfDNA.
In a recent study, levels of tumor cfDNA were evaluated in 410 patients with solid tumors . The fraction of patients with detectable levels of cfDNA varied among tumor types. Most patients with stage III ovarian or liver cancer, as well as most patients with neuroblastoma or melanoma, had measurable levels of cfDNA. In addition, most patients with metastatic cancers of the pancreas, bladder, colon, stomach, breast, liver, esophagus or head and neck had measurable levels of cfDNA. Notably, less than 50% of the patients with medulloblastomas or metastatic cancers of the kidney, prostate or thyroid, and less than 10% of patients with gliomas harbored detectable cfDNA. A likely explanation for the low amount of cfDNA in patients with tumors localized to the central nervous system is the presence of the blood-brain barrier .
Molecular profiles of solid cancer from cfDNA
Defining the tumor genotype of an individual patient is becoming part of the standard of care for a significant proportion of cancer patients. Genotyping can be used in several settings: to categorize the type and the stage of cancer, to establish the aggressiveness of the disease, to tailor treatment and to monitor evolution of the cancer during therapy.
Currently, the genotype of a tumor is established from tumor tissue, which is obtained through surgically or radiologically guided biopsies. However, sampling tumor tissue in this way has significant, inherent limitations. Molecular profiling of tumor tissue provides a single snapshot in time, is subject to selection bias owing to tumor heterogeneity and does not capture the complexity of the disease if multiple metastatic lesions are present -,.
When a comprehensive analysis of the overall disease is required or when tissue specimens are difficult to obtain or are unavailable, liquid biopsies are an attractive alternative option. This is because circulating tumor DNA fragments contain identical genetic defects to those in the tumors themselves and virtually all cancer-related molecular alterations can be detected in cfDNA. These include somatic point mutations, loss of heterozygosity (LOH), translocations, gene copy number changes and DNA methylation changes. For example, oncogenic alterations such as mutations in KRAS (Kirsten rat sarcoma viral oncogene homolog), BRAF (B-Raf proto-oncogene, serine/threonine kinase), PIK3CA (phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha) and EGFR (epidermal growth factor receptor) can be readily detected in the blood of patients with lung, colorectal, breast or pancreatic cancer, or melanoma. Mutations that inactivate common tumor suppressor genes such as APC (adenomatous polyposis coli) and TP53 (tumor protein p53) have also been detected in the plasma of cancer patients ,. Gene copy number variations, such as amplification of EGFR, HER2 (human epidermal growth factor receptor 2) and MET (MET proto-oncogene, receptor tyrosine kinase), can also be detected in the blood -.
Clinical applications of liquid biopsies
Monitoring minimal residual disease
Surgery with curative intent is used for many cancer patients. A central question is whether further therapy is needed after surgical removal of the cancer. Currently, predicting which patients are disease-free after surgery (cured) and those who have residual disease depends largely on clinical and pathological parameters (mainly the tumor-node-metastasis staging system). There is currently no effective diagnostic means to distinguish between those patients that are disease-free and those with minimal residual disease that cannot be detected by clinical examination or imaging. Undetected, untreated minimal residual disease gives rise to recurrences. As a result, patients with high-risk clinical and pathological criteria are indiscriminately treated with adjuvant chemotherapy. Unfortunately, this therapy is frequently not needed because the patient would have been cured with surgery and/or radiotherapy alone.
Liquid biopsies have great potential in this scenario. The detection of tumor cfDNA following surgery/radiotherapy would be an indicator of residual disease, and hence liquid biopsies could be used to identify those patients who would benefit from adjuvant therapy while sparing those who would not benefit from unnecessary treatment. Detection of tumor cfDNA after completion of surgery/radiotherapy would indicate the presence of micro-metastasis and much greater risk of relapse, indicating a need for adjuvant therapy. Moreover, the detection of tumor cfDNA would indicate early relapse and could potentially be used to tailor targeted therapy to the patient  (Figure 2).
Recently, Beaver and colleagues  studied tumor cfDNA to detect PIK3CA mutations and to monitor residual disease after surgery in patients with early stage breast cancer. Primary breast tumors and matched pre- and post-surgery blood samples were collected from early-stage breast cancer patients. The study was conducted prospectively, which adds considerable relevance to the findings. Droplet digital PCR (ddPCR) was used to assess the presence of PIK3CA mutations (in exon 9 and 20) in the blood of estrogen-receptor- and progesterone-receptor-positive early-stage breast cancer patients. DNA extracted from 30 tumor samples was analyzed by Sanger sequencing for common PIK3CA mutations; 10 samples were found to carry PIK3CA mutations. The same 30 samples were analyzed by ddPCR, which identified five more patients carrying PIK3CA mutations. Plasma cfDNA was then isolated from pre- and post-operative blood samples. In 14 of the 15 samples with mutations, those mutations were detected in pre-surgery plasma samples by ddPCR, whereas no mutations were found in the pre-surgery samples in which post-surgery samples showed no mutations. The sensitivity and specificity of cfDNA analysis to detect mutations were thus remarkable (93.3% and 100%, respectively). Among 10 of the patients with mutation-positive pre-surgery tumor cfDNA, analysis of post-surgery plasma detected PIK3CA mutations in five. These patients had no other clinical evidence of disease by any radiological examination the patients were subjected to. Overall, the work of Beaver and colleagues  presents the first evidence that a 'liquid biopsy' approach can be used to identify patients with breast cancers at early stages and at risk of recurrence after surgery.
Liquid biopsy can also be used to monitor tumor dynamics in a cancer patient. For example, assessing the fluctuations of an APC mutation, which is known to be the initiating lesion in colorectal cancer tumorigenesis, during the follow-up of a patient provides a measure of the systemic tumor burden, because levels of the mutation in circulating DNA decrease following surgery and increase as new lesions appear (as detected by radiological examination) .
Tracking emergence of drug resistance
In the past decade, drugs that target genetically defined tumor vulnerabilities (such as EGFR or BRAF mutations) have shown remarkable effectiveness . Acquired resistance, which is observed in virtually all patients following treatment with anticancer drugs, limits the utility of these drugs and is a substantial challenge to the clinical management of cancer patients. Accordingly, understanding the molecular basis and development of acquired resistance is key to trying to overcome it. Analysis of tumor cfDNA provides a valuable opportunity to repeatedly monitor molecular response during targeted treatment and detect early evidence of emerging resistance (such as specific mutations) and tumor recurrence, as described below ,,-.
Tracking the genomic evolution of cancer during therapy is an unmet clinical need. As discussed above, tissue biopsies reveal only a fraction of the overall disease heterogeneity, especially in patients with metastatic disease. It is fair to say that no effective means currently exists to assess the molecular evolution of the overall disease during the course of therapy in patients with multiple metastatic lesions in distinct organs.
In contrast, tumor cfDNA analysis enables early identification of molecular changes associated with drug resistance and can be easily repeated multiple times in one patient.
Conclusions and future directions
Liquid biopsies can improve the effectiveness of precision oncology, with potential benefits to patients and healthcare systems. Research on liquid biopsies has seen enormous development in the past 5 years; this has led to a proliferation of publications, most of which involve very small numbers of patients. None of these studies presented definitive evidence as to how the analysis of tumor cfDNA may be clinically relevant or applicable ,,-,,-. What the field needs are well-controlled clinical studies, involving extensive cohorts of patients, in which liquid biopsies are used to address clinically relevant questions. We propose that these studies should focus on two questions: the development of non-invasive tests to detect minimal residual disease in patients affected by solid cancers; and the use of liquid biopsies to monitor the emergence of molecular resistance to anticancer therapies before relapse is clinically manifest. This could lead to the early adoption of further lines of therapy.
Adenomatous polyposis coli
B-Raf proto-oncogene, serine/threonine kinase
cell-free nucleic acid
droplet digital PCR
Human epidermal growth factor receptor 2
Kirsten rat sarcoma viral oncogene homolog
loss of heterozygosity
MET proto-oncogene, receptor tyrosine kinase
Phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha
Tumor protein p53
European Community's Seventh Framework Programme under grant agreement n. 259015 COLTHERES; AIRC 2010 Special Program Molecular Clinical Oncology 5 per mille, project n. 9970; AIRC IG n. 12812; Fondazione Piemontese per la Ricerca sul Cancro-ONLUS 5 per mille 2010 Ministero della Salute; Ministero dell'Istruzione, dell'Università e della Ricerca (progetto PRIN).
- Diaz LA, Bardelli A: Liquid biopsies: genotyping circulating tumor DNA. J Clin Oncol. 2014, 32: 579-586. 10.1200/JCO.2012.45.2011.PubMedView ArticleGoogle Scholar
- Pantel K, Alix-Panabières C: Real-time liquid biopsy in cancer patients: fact or fiction?. Cancer Res. 2013, 73: 6384-6388. 10.1158/0008-5472.CAN-13-2030.PubMedView ArticleGoogle Scholar
- Pantel K, Diaz LA, Polyak K: Tracking tumor resistance using 'liquid biopsies'. Nat Med. 2013, 19: 676-677. 10.1038/nm.3233.PubMedView ArticleGoogle Scholar
- Mandel P, Metais P: Les acides nucleiques du plasma sanguin chez l'homme. C R Seances Soc Biol Fil. 1948, 142: 241-243.PubMedGoogle Scholar
- Leon SA, Shapiro B, Sklaroff DM, Yaros MJ: Free DNA in the serum of cancer patients and the effect of therapy. Cancer Res. 1977, 37: 646-650.PubMedGoogle Scholar
- Stroun M, Anker P, Maurice P, Lyautey J, Lederrey C, Beljanski M: Neoplastic characteristics of the DNA found in the plasma of cancer patients. Oncology. 1989, 46: 318-322. 10.1159/000226740.PubMedView ArticleGoogle Scholar
- Vasioukhin V, Anker P, Maurice P, Lyautey J, Lederrey C, Stroun M: Point mutations of the N-ras gene in the blood plasma DNA of patients with myelodysplastic syndrome or acute myelogenous leukaemia. Br J Haematol. 1994, 86: 774-779. 10.1111/j.1365-2141.1994.tb04828.x.PubMedView ArticleGoogle Scholar
- Sorenson GD, Pribish DM, Valone FH, Memoli VA, Bzik DJ, Yao SL: Soluble normal and mutated DNA sequences from single-copy genes in human blood. Cancer Epidemiol Biomarkers Prev. 1994, 3: 67-71.PubMedGoogle Scholar
- Nawroz H, Koch W, Anker P, Stroun M, Sidransky D: Microsatellite alterations in serum DNA of head and neck cancer patients. Nat Med. 1996, 2: 1035-1037. 10.1038/nm0996-1035.PubMedView ArticleGoogle Scholar
- Chen XQ, Stroun M, Magnenat JL, Nicod LP, Kurt AM, Lyautey J, Lederrey C, Anker P: Microsatellite alterations in plasma DNA of small cell lung cancer patients. Nat Med. 1996, 2: 1033-1035. 10.1038/nm0996-1033.PubMedView ArticleGoogle Scholar
- Anker P, Lefort F, Vasioukhin V, Lyautey J, Lederrey C, Chen XQ, Stroun M, Mulcahy HE, Farthing MJ: K-ras mutations are found in DNA extracted from the plasma of patients with colorectal cancer. Gastroenterology. 1997, 112: 1114-1120. 10.1016/S0016-5085(97)70121-5.PubMedView ArticleGoogle Scholar
- Silva JM, Dominguez G, Villanueva MJ, Gonzalez R, Garcia JM, Corbacho C, Provencio M, España P, Bonilla F: Aberrant DNA methylation of the p16INK4a gene in plasma DNA of breast cancer patients. Br J Cancer. 1999, 80: 1262-1264. 10.1038/sj.bjc.6690495.PubMedPubMed CentralView ArticleGoogle Scholar
- Silva JM, Gonzalez R, Dominguez G, Garcia JM, España P, Bonilla F: TP53 gene mutations in plasma DNA of cancer patients. Genes Chromosomes Cancer. 1999, 24: 160-161. 10.1002/(SICI)1098-2264(199902)24:2<160::AID-GCC10>3.0.CO;2-C.PubMedView ArticleGoogle Scholar
- Murtaza M, Dawson SJ, Tsui DW, Gale D, Forshew T, Piskorz AM, Parkinson C, Chin SF, Kingsbury Z, Wong AS, Marass F, Humphray S, Hadfield J, Bentley D, Chin TM, Brenton JD, Caldas C, Rosenfeld N: Non-invasive analysis of acquired resistance to cancer therapy by sequencing of plasma DNA. Nature. 2013, 497: 108-112. 10.1038/nature12065.PubMedView ArticleGoogle Scholar
- Jen J, Wu L, Sidransky D: An overview on the isolation and analysis of circulating tumor DNA in plasma and serum. Ann N Y Acad Sci. 2000, 906: 8-12. 10.1111/j.1749-6632.2000.tb06581.x.PubMedView ArticleGoogle Scholar
- Thijssen MA, Swinkels DW, Ruers TJ, de Kok JB: Difference between free circulating plasma and serum DNA in patients with colorectal liver metastases. Anticancer Res. 2002, 22: 421-425.PubMedGoogle Scholar
- Lee TH, Montalvo L, Chrebtow V, Busch MP: Quantitation of genomic DNA in plasma and serum samples: higher concentrations of genomic DNA found in serum than in plasma. Transfusion. 2001, 41: 276-282. 10.1046/j.1537-2995.2001.41020276.x.PubMedView ArticleGoogle Scholar
- Steinman CR: Free DNA in serum and plasma from normal adults. J Clin Invest. 1975, 56: 512-515. 10.1172/JCI108118.PubMedPubMed CentralView ArticleGoogle Scholar
- Chan KC, Yeung SW, Lui WB, Rainer TH, Lo YM: Effects of preanalytical factors on the molecular size of cell-free DNA in blood. Clin Chem. 2005, 51: 781-784. 10.1373/clinchem.2004.046219.PubMedView ArticleGoogle Scholar
- Jung M, Klotzek S, Lewandowski M, Fleischhacker M, Jung K: Changes in concentration of DNA in serum and plasma during storage of blood samples. Clin Chem. 2003, 49: 1028-1029. 10.1373/49.6.1028.PubMedView ArticleGoogle Scholar
- Thierry AR, Mouliere F, Gongora C, Ollier J, Robert B, Ychou M, Del Rio M, Molina F: Origin and quantification of circulating DNA in mice with human colorectal cancer xenografts. Nucleic Acids Res. 2010, 38: 6159-6175. 10.1093/nar/gkq421.PubMedPubMed CentralView ArticleGoogle Scholar
- El Messaoudi S, Rolet F, Mouliere F, Thierry AR: Circulating cell free DNA: Preanalytical considerations. Clin Chim Acta. 2013, 424: 222-230. 10.1016/j.cca.2013.05.022.PubMedView ArticleGoogle Scholar
- Fleischhacker M, Schmidt B: Circulating nucleic acids (CNAs) and cancer–a survey. Biochim Biophys Acta. 2007, 1775: 181-232.PubMedGoogle Scholar
- Stroun M, Maurice P, Vasioukhin V, Lyautey J, Lederrey C, Lefort F, Rossier A, Chen XQ, Anker P: The origin and mechanism of circulating DNA. Ann N Y Acad Sci. 2000, 906: 161-168. 10.1111/j.1749-6632.2000.tb06608.x.PubMedView ArticleGoogle Scholar
- Gahan PB, Swaminathan R: Circulating nucleic acids in plasma and serum. Recent developments. Ann N Y Acad Sci. 2008, 1137: 1-6. 10.1196/annals.1448.050.PubMedView ArticleGoogle Scholar
- Stroun M, Lyautey J, Lederrey C, Olson-Sand A, Anker P: About the possible origin and mechanism of circulating DNA apoptosis and active DNA release. Clin Chim Acta. 2001, 313: 139-142. 10.1016/S0009-8981(01)00665-9.PubMedView ArticleGoogle Scholar
- Properzi F, Logozzi M, Fais S: Exosomes: the future of biomarkers in medicine. Biomark Med. 2013, 7: 769-778. 10.2217/bmm.13.63.PubMedView ArticleGoogle Scholar
- Muller L, Hong CS, Stolz DB, Watkins SC, Whiteside TL: Isolation of biologically-active exosomes from human plasma. J Immunol Methods. 2014Google Scholar
- Thakur BK, Zhang H, Becker A, Matei I, Huang Y, Costa-Silva B, Zheng Y, Hoshino A, Brazier H, Xiang J, Williams C, Rodriguez-Barrueco R, Silva JM, Zhang W, Hearn S, Elemento O, Paknejad N, Manova-Todorova K, Welte K, Bromberg J, Peinado H, Lyden D: Double-stranded DNA in exosomes: a novel biomarker in cancer detection. Cell Res. 2014, 24: 766-769. 10.1038/cr.2014.44.PubMedPubMed CentralView ArticleGoogle Scholar
- Diehl F, Li M, Dressman D, He Y, Shen D, Szabo S, Diaz LA, Goodman SN, David KA, Juhl H, Kinzler KW, Vogelstein B: Detection and quantification of mutations in the plasma of patients with colorectal tumors. Proc Natl Acad Sci U S A. 2005, 102: 16368-16373. 10.1073/pnas.0507904102.PubMedPubMed CentralView ArticleGoogle Scholar
- Jahr S, Hentze H, Englisch S, Hardt D, Fackelmayer FO, Hesch RD, Knippers R: DNA fragments in the blood plasma of cancer patients: quantitations and evidence for their origin from apoptotic and necrotic cells. Cancer Res. 2001, 61: 1659-1665.PubMedGoogle Scholar
- Chun FK, Müller I, Lange I, Friedrich MG, Erbersdobler A, Karakiewicz PI, Graefen M, Pantel K, Huland H, Schwarzenbach H: Circulating tumour-associated plasma DNA represents an independent and informative predictor of prostate cancer. BJU Int. 2006, 98: 544-548. 10.1111/j.1464-410X.2006.06352.x.PubMedView ArticleGoogle Scholar
- Allen D, Butt A, Cahill D, Wheeler M, Popert R, Swaminathan R: Role of cell-free plasma DNA as a diagnostic marker for prostate cancer. Ann N Y Acad Sci. 2004, 1022: 76-80. 10.1196/annals.1318.013.PubMedView ArticleGoogle Scholar
- Schwarzenbach H, Stoehlmacher J, Pantel K, Goekkurt E: Detection and monitoring of cell-free DNA in blood of patients with colorectal cancer. Ann N Y Acad Sci. 2008, 1137: 190-196. 10.1196/annals.1448.025.PubMedView ArticleGoogle Scholar
- Sunami E, Vu AT, Nguyen SL, Giuliano AE, Hoon DS: Quantification of LINE1 in circulating DNA as a molecular biomarker of breast cancer. Ann N Y Acad Sci. 2008, 1137: 171-174. 10.1196/annals.1448.011.PubMedView ArticleGoogle Scholar
- Raptis L, Menard HA: Quantitation and characterization of plasma DNA in normals and patients with systemic lupus erythematosus. J Clin Invest. 1980, 66: 1391-1399. 10.1172/JCI109992.PubMedPubMed CentralView ArticleGoogle Scholar
- Shapiro B, Chakrabarty M, Cohn EM, Leon SA: Determination of circulating DNA levels in patients with benign or malignant gastrointestinal disease. Cancer. 1983, 51: 2116-2120. 10.1002/1097-0142(19830601)51:11<2116::AID-CNCR2820511127>3.0.CO;2-S.PubMedView ArticleGoogle Scholar
- Bettegowda C, Sausen M, Leary RJ, Kinde I, Wang Y, Agrawal N, Bartlett BR, Wang H, Luber B, Alani RM, Antonarakis ES, Azad NS, Bardelli A, Brem H, Cameron JL, Lee CC, Fecher LA, Gallia GL, Gibbs P, Le D, Giuntoli RL, Goggins M, Hogarty MD, Holdhoff M, Hong SM, Jiao Y, Juhl HH, Kim JJ, Siravegna G, Laheru DA, et al: Detection of circulating tumor DNA in early- and late-stage human malignancies. Sci Transl Med. 2014, 6: 224ra224-10.1126/scitranslmed.3007094.View ArticleGoogle Scholar
- Holdhoff M, Schmidt K, Donehower R, Diaz LA: Analysis of circulating tumor DNA to confirm somatic KRAS mutations. J Natl Cancer Inst. 2009, 101: 1284-1285. 10.1093/jnci/djp240.PubMedView ArticleGoogle Scholar
- Diehl F, Schmidt K, Choti MA, Romans K, Goodman S, Li M, Thornton K, Agrawal N, Sokoll L, Szabo SA, Kinzler KW, Vogelstein B, Diaz LA: Circulating mutant DNA to assess tumor dynamics. Nat Med. 2008, 14: 985-990. 10.1038/nm.1789.PubMedPubMed CentralView ArticleGoogle Scholar
- Bardelli A, Corso S, Bertotti A, Hobor S, Valtorta E, Siravegna G, Sartore-Bianchi A, Scala E, Cassingena A, Zecchin D, Apicella M, Migliardi G, Galimi F, Lauricella C, Zanon C, Perera T, Veronese S, Corti G, Amatu A, Gambacorta M, Diaz LA, Sausen M, Velculescu VE, Comoglio P, Trusolino L, Di Nicolantonio F, Giordano S, Siena S: Amplification of the MET receptor drives resistance to anti-EGFR therapies in colorectal cancer. Cancer Discov. 2013, 3: 658-673. 10.1158/2159-8290.CD-12-0558.PubMedPubMed CentralView ArticleGoogle Scholar
- Leary RJ, Sausen M, Diaz LA, Velculescu VE: Cancer detection using whole-genome sequencing of cell free DNA. Oncotarget. 2013, 4: 1119-1120.PubMedPubMed CentralView ArticleGoogle Scholar
- Diaz LA, Sausen M, Fisher GA, Velculescu VE: Insights into therapeutic resistance from whole-genome analyses of circulating tumor DNA. Oncotarget. 2013, 4: 1856-1857.PubMedPubMed CentralView ArticleGoogle Scholar
- Mohan S, Heitzer E, Ulz P, Lafer I, Lax S, Auer M, Pichler M, Gerger A, Eisner F, Hoefler G, Bauernhofer T, Geigl JB, Speicher MR: Changes in colorectal carcinoma genomes under anti-EGFR therapy identified by whole-genome plasma DNA sequencing. PLoS Genet. 2014, 10: e1004271-10.1371/journal.pgen.1004271.PubMedPubMed CentralView ArticleGoogle Scholar
- Wimberger P, Roth C, Pantel K, Kasimir-Bauer S, Kimmig R, Schwarzenbach H: Impact of platinum-based chemotherapy on circulating nucleic acid levels, protease activities in blood and disseminated tumor cells in bone marrow of ovarian cancer patients. Int J Cancer. 2011, 128: 2572-2580. 10.1002/ijc.25602.PubMedView ArticleGoogle Scholar
- Beaver JA, Jelovac D, Balukrishna S, Cochran RL, Croessmann S, Zabransky DJ, Wong HY, Valda Toro P, Cidado J, Blair BG, Chu D, Burns T, Higgins MJ, Stearns V, Jacobs L, Habibi M, Lange J, Hurley PJ, Lauring J, VanDenBerg DA, Kessler J, Jeter S, Samuels ML, Maar D, Cope L, Cimino-Mathews A, Argani P, Wolff AC, Park BH: Detection of cancer DNA in plasma of early stage breast cancer patients. Clin Cancer Res. 2014, 20: 2643-2650. 10.1158/1078-0432.CCR-13-2933.PubMedPubMed CentralView ArticleGoogle Scholar
- Martini M, Vecchione L, Siena S, Tejpar S, Bardelli A: Targeted therapies: how personal should we go?. Nat Rev Clin Oncol. 2012, 9: 87-97. 10.1038/nrclinonc.2011.164.View ArticleGoogle Scholar
- Dawson SJ, Tsui DW, Murtaza M, Biggs H, Rueda OM, Chin SF, Dunning MJ, Gale D, Forshew T, Mahler-Araujo B, Rajan S, Humphray S, Becq J, Halsall D, Wallis M, Bentley D, Caldas C, Rosenfeld N: Analysis of circulating tumor DNA to monitor metastatic breast cancer. N Engl J Med. 2013, 368: 1199-1209. 10.1056/NEJMoa1213261.PubMedView ArticleGoogle Scholar
- Dawson SJ, Rosenfeld N, Caldas C: Circulating tumor DNA to monitor metastatic breast cancer. N Engl J Med. 2013, 369: 93-94. 10.1056/NEJMc1306040.PubMedView ArticleGoogle Scholar
- Diaz LA, Williams RT, Wu J, Kinde I, Hecht JR, Berlin J, Allen B, Bozic I, Reiter JG, Nowak MA, Kinzler KW, Oliner KS, Vogelstein B: The molecular evolution of acquired resistance to targeted EGFR blockade in colorectal cancers. Nature. 2012, 486: 537-540.PubMedPubMed CentralGoogle Scholar
- Kuang Y, Rogers A, Yeap BY, Wang L, Makrigiorgos M, Vetrand K, Thiede S, Distel RJ, Jänne PA: Noninvasive detection of EGFR T790M in gefitinib or erlotinib resistant non-small cell lung cancer. Clin Cancer Res. 2009, 15: 2630-2636. 10.1158/1078-0432.CCR-08-2592.PubMedPubMed CentralView ArticleGoogle Scholar
- Misale S, Yaeger R, Hobor S, Scala E, Janakiraman M, Liska D, Valtorta E, Schiavo R, Buscarino M, Siravegna G, Bencardino K, Cercek A, Chen CT, Veronese S, Zanon C, Sartore-Bianchi A, Gambacorta M, Gallicchio M, Vakiani E, Boscaro V, Medico E, Weiser M, Siena S, Di Nicolantonio F, Solit D, Bardelli A: Emergence of KRAS mutations and acquired resistance to anti-EGFR therapy in colorectal cancer. Nature. 2012, 486: 532-536.PubMedPubMed CentralGoogle Scholar
This article is published under license to BioMed Central Ltd. The licensee has exclusive rights to distribute this article, in any medium, for 12 months following its publication. After this time, the article is available under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.