Search tips
Search criteria 


Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
FEBS Lett. Author manuscript; available in PMC 2011 June 18.
Published in final edited form as:
PMCID: PMC2892754

Oncogenic mutant forms of EGFR: lessons in signal transduction and targets for cancer therapy


The EGF receptor is frequently mutated in a large variety of tumors. Here we review the most frequent mutations and conclude that they commonly enhance the intrinsic tyrosine kinase activity, or they represent loss-of-function of suppressive regulatory domains. Interestingly, the constitutive activity of mutant receptors translates to downstream pathways, which are subtly different from those stimulated by the wild type receptor. Cancer drugs intercepting EGFR signaling have already entered clinical application. Both kinase inhibitors specific to EGFR, and monoclonal antibodies to the receptor are described, along with experimental approaches targeting the HSP90 chaperone. Deeper understanding of signaling pathways downstream to mutant receptors will likely improve the outcome of current EGFR-targeted therapies, as well as help develop new drugs and combinations.


The laboratory of Stanley Cohen discovered in 1980 that addition of EGF to the culture medium of human epidermoid carcinoma (A431) cells yields massive tyrosine phosphorylation, similarly to cells infected with oncogenic viruses [1]. Although not known at the time, it was speculated by Stanley Cohen and colleagues, that the EGF-receptor (EGFR) and the observed kinase activity are present in the same molecule [2]. In the past thirty years we have learned a great deal about the structure of growth factor receptors, their intrinsic ligand recognition and kinase functions, and the cellular outcomes of their activation. Upon their ligand-induced dimerization, growth factor receptors initiate a vast array of cell signaling pathways (Fig. 1), with profound effects on cell fate decisions such as proliferation, cell lineage determination and differentiation, migration and even cell death. Due to their importance, these mechanisms evolved to be tightly regulated and robust. One of the best-studied examples for such mechanisms is the EGFR family, also called the ErbB family, which belongs to the super-family of receptor tyrosine kinases (RTKs). These plasma membrane bound receptors are mainly composed of an extracellular ligand-binding, and a single trans-membrane domain, followed by an intracellular tyrosine kinase domain and a non-catalytic carboxyl terminal tail. This configuration allows extracellular signals to be relayed into the cell, and to be interpreted in order to evoke a proper response: Activation is achieved following a series of processes starting with the interaction between the ligand and the ligand-binding domain of the receptor. This binding induces a structural change which exposes an otherwise tethered dimerization arm [3], leading to coupling of two receptor molecules. Now, closer together in the correct orientation, the two kinase domains interact asymmetrically, while one kinase acts as an activator and the second being activated [4]. The activated kinase phosphorylates tyrosine residues located at the receptor’s tail, which then act as docking sites for adaptor molecules linking the receptor to its downstream signaling pathways (Fig. 1).

Figure 1
Activation mechanisms and signaling pathways engaged by EGFR

During evolution, the single nematode ErbB receptor, Let-23, underwent two duplication events and subsequent incorporation of further mutations, resulting in a family of four members in mammals [5], which seem to be similar at the first glance, but were discovered to be profoundly different [6,7]. While ligand binding activates the kinase domain of EGFR/ErbB-1, as well as ErbB4, ErbB-2 has no compatible ligand and is kept in a constitutively active state [8]. On the other hand, ErbB-3 maintained its ligand-binding capacity, but its kinase domain was mutated in a way that it can only serve as a catalytically inactive activator of kinases in the context of ErbB receptor heterodimers [9]. Owing to their significant similarities, these receptors may form homo- as well as hetero-dimers, upon ligand binding, thus assembling a spectrum of activation options [10]. To further increase this system’s complexity, ligands have evolved as well and are composed of a family of eleven molecules, distinct with respect to their expression patterns, binding specificities and affinities to the ErbB receptors [1116]. Remarkably, each ligand is unique in multiple aspects, which determine physiological roles, as well as oncogenicity. These include cleavage of the precursor form, retention in the extracellular environment, preference for certain receptor heterodimers and intracellular trafficking.

Despite multiple regulatory mechanisms acting at the levels of receptors and their downstream signaling pathways, which increase the robustness of this system, the ErbB family represents a major player in many types of malignancies. Robust as it is, every complex system has its weaknesses, and the ErbB system is not different: cellular transformation can arise from receptor gene amplification or overexpression, which is thought to promote dimerization by their shear numbers [17], or, conversely, by self-production of ligands, which initiate signaling cascades in an autocrine manner [18]. A third option of short-circuiting this highly regulated system is to bypass some of its inherent control. In this review, we will focus on the regulatory elements imposed by the molecular structure of EGFR, along with the question how cancer mutated its way to overcome these regulatory elements. In addition, we will highlight therapeutic approaches aiming to overcome aberrant modes of EGFR activation.

EGFR mutations are not random

Mutant forms of EGFR have been found in several human tumor types. The aberrant forms characterize a limited set of tumors, but their causes and reasons for cell lineage specificity remain unknown. In addition, these alterations are not evenly dispersed along the EGFR gene, but rather cluster in specific areas, leading to the assumption that mutational “hot spots” entail elements of special functional or regulatory importance (Fig. 2).

Figure 2
Receptor aberrations cluster in functionally relevant hotspots of EGFR

The ectodomain hotspot

A primary safeguard mechanism, which prevents premature receptor dimerization and subsequent activation, is the ligand-binding domain. Formation of stable receptor dimers can only be achieved upon ligand binding, followed by a constructive dimer formation. The viral EGFR homologue, v-ErbB, which induces erythroblastosis in birds and contributed its name to the ErbB family, lacks the whole extracellular domain. With the dimerization constrains removed, this viral protein was found to exist primarily in dimers, leading to constitutive kinase activation and subsequent oncogenicity [19]. Interestingly, similar deletion mutants have been discovered in human gliomas (Table 1 and Fig. 2). One of these mutant forms, EGFR variant III (EGFRvIII), was found to lack a large part of the extracellular portion, including components of the ligand-binding domain [20]. Indeed, although ligand insensitive, this mutated form was found to be constitutively dimerized and highly tumorigenic [21], resembling the activity of its viral counterpart. Additionally, apart from deletions, this ectodomain’s hot spot attracts point mutations, most of which were reported to be oncogenic [22], presumably by promoting receptor dimerization.

Table 1
Common EGFR mutations

The kinase hotspot

Unlike other RTKs, which must undergo phosphorylation within the activation loop of the kinase domain in order to achieve the catalytically active conformation, EGFR does not require this modification [23]. Here, the activity of the kinase domain is controlled by conformational changes induced by dimer formation and possibly by the distal carboxyl terminus. Following the rationale of regulation-bypassing, Non-Small Cell Lung Cancer (NSCLC) and other tumors harbor point mutations, small deletions or insertions of the EGFR kinase domain [2426], rendering this domain constitutively active [27] even in the absence of upstream events such as ligand binding or dimerization.

The C-tail hotspot

In addition to activation by means of kinase mutations, a deletion mutant found in gliomas, named EGFRvIV, lacks either two or three exons in its carboxyl tail, downstream to the kinase domain [20,28], while keeping most of the auto-phosphorylation tyrosine residues intact. According to structural [29,30] and computational analyses, the deleted segment likely plays an essential role in kinase auto-regulation by folding over the kinase domain, implying that its removal will result in constitutive kinase activity [31]. Additionally, the notion of a regulatory role of the carboxyl tail may explain the constitutive activation of a kinase-duplication mutant, in which only one kinase is predicted to be inhibited by the tail, while the other may represent an active form [32].

Pathologic aspects of the common oncogenic mutants of EGFR (see Table 1) EGFRvIII in brain and other tumors

Since its discovery in 1990 [33], EGFRvIII has been a subject of thorough investigation, which is justified by its relative abundance in brain tumors, and frequent detection in other malignancies, including lung, breast and ovarian cancers [20,3436]. As mentioned above, by deletion of a segment of the ligand-binding domain, EGFRvIII bypasses the need of ligand. This deletion spans exons 2–7, resulting in the introduction of a novel glycine residue at the fusion junction. Interestingly, EGFRvIII is commonly diagnosed in tumors that overexpress the wild type form of EGFR, suggesting that receptor overexpression precedes deletion of exons 2–7 [28,33]. While this mutant cannot bind ligands, it resides at the cell membrane [37], often within receptor dimers [38] that display constitutive basal activity. EGFRvIII has been shown to be transforming both in vitro and in vivo, as it confers anchorage-independent growth of cultured cells and promotes tumor formation in athymic mice [39]. Curiously, the oncogenic capacity of EGFRvIII may propagate into non-expressing cells by means of cell-to-cell transfer of membrane-derived microvesicles [40].

Kinase mutations in NSCLC

Mutations in the EGFR kinase domain are often diagnosed in NSCLC, particularly in tumors occurring in individuals of Eastern Asian origin, females, never smokers, and in adenocarcinomas with bronchioloalveolar histological features [41,42]. These mutations spread along the kinase-coding regions (exons 18–21), and they all seem to catalytically stimulate the basal kinase activity, although by different means. Exons 18 and 19 encode for the phosphate-binding loop, also termed the P-loop. While exon 18 displays point mutations, mainly G719X (X indicates A, C, S or D), which represent about 4% of EGFR mutations in NSCLC, exon 19 is usually affected by deletions, which represent 44% of kinase domain mutations. Exon 20, which encodes for the α-C helix, harbors relatively rare (4%) insertion mutations, whereas exon 21, encoding the activation loop (A loop), encompasses point mutations that account for 41% of mutations, including the prototypical L858R mutation [43]. All these mutations are believed to destabilize the inactive kinase conformation, hence driving it to a more active state [44]. Notably, in contrast to EGFRvIII, kinase-mutated EGF receptors retain their responsiveness to growth factor ligands [45], which further enhance catalytic activity, relatively to wild type EGFR [24].

Novel signal transduction features of EGFR mutants

Even though the mutated EGF-receptors that are frequently found in tumors were proven to be catalytically active and tumorigenic, their activation profile is essentially different than that of the ligand-activated wild type receptor. Usually, EGFR tyrosine phosphorylation status is significantly lower in mutated receptors compared to ligand-activated wild type receptors, yet clearly exceeds its unstimulated state. Apparently, this basal but chronic activity relays signals in a profoundly different manner than the well-characterized canonical signal-transduction machinery.

The case of EGFRvIII

An example for such discrepancy between wild type and mutant signaling potentials is EGFRvIII activation: while the wild type EGFR activates several signaling pathways upon ligand binding (Fig. 1), the constitutively-dimerized mutant preferentially activates the Phosphatidylinositol 3-Kinase (PI3K) pathway over other pathways such as the Mitogen-Activated Protein Kinase (MAPK) pathway [4648]. Indeed, EGFRvIII instigates the expression of only a subset of genes induced by the ligand-stimulated wild type EGFR [49].

Mutant EGFRs escape negative regulation

Another important feature of the relatively high basal signaling of EGFR mutants is their ability to evade negative, activation-dependent regulation. The customary EGFR signal attenuator is the ubiquitin-ligase CBL, which is recruited to a specific phosphorylated tyrosine residue located at the receptor’s tail (Y1045). When bound, CBL attaches mono-and di-ubiquitin moieties to multiple lysine residues of EGFR, thus tagging the receptor for lysosomal degradation, and thereby defining the temporal window of signaling of activated EGFR. Apparently, in some cases, including the NSCLC single (L858R) and double mutant (L858R/T790M), basal EGFR activation results in differential phosphorylation of tail tyrosine residues [22,5052], allowing uncontrolled downstream signaling. This aberrant activation pattern is achieved by phosphorylation of tyrosine residues responsible for propagating the signal downstream, while Y1045 is kept at a weakly phosphorylated state, thus allowing the mutated receptors to signal “under the radar” of receptor attenuating mechanisms.

Cancer therapies targeting aberrant forms of EGFR

Due to the frequent involvement of the ErbB family in cancer, intercepting its members became a natural goal of the targeted therapy approach. In contrast to chemotherapy, which is highly toxic and often results in adverse clinical effects, targeted therapy aims specifically at the relevant renegade protein. Although tumors harbor multiple genetic abnormalities, according to the “oncogene addiction” theory, their tumorigenic drive may be attributed to a single pathway, to which the tumor became “addicted” [53]. Indeed, in many cases, when this pathway is pharmacologically blocked, cancer cells die, leading to tumor regression. A related theory, termed the “oncogenic shock”, proposes that short-lived pro-survival signals are depleted due to treatment, leaving the cell with long-lived pro-apoptotic elements that drive cell death [54]. Regardless of the mechanism, RTK targeting has been proven beneficial across a wide spectrum of malignancies. Accordingly, ErbB proteins and other RTKs are currently directly targeted using two distinct strategies (Fig. 3):

Figure 3
Therapies targeting EGFR signaling

Tyrosine kinase inhibitors

One of the outcomes of the pursuit for EGFR inhibiting agents was the development of small molecules that bind to the ATP-binding pocket of the kinase domain, thereby inhibiting its enzymatic activity. These Tyrosine Kinase Inhibitors (TKIs) mimic ATP, which serves as phosphate source for the phosphorylation process [55]. TKIs may bind either reversibly or irreversibly, and their specificity can be designed to target EGFR alone, several ErbB family members, or even other tyrosine kinases as well. Two such molecules, Erlotinib (OSI-774, Tarceva®) and Gefitinib (ZD 1839, Iressa®) are reversible EGFR-specific TKIs, which are already in clinical use for treatment of NSCLC and pancreatic adenocarcinomas [5659]. A third approved compound, lapatinib/Tykerb® inhibits both EGFR and its closest kin, HER2/ErbB-2, and is successfully used in patients with HER2-overexpressing metastatic breast cancer [60,61].

Monoclonal anti-receptor antibodies

The first broadly successful monoclonal antibody (mAb) to target the ErbB system in human malignancies was trastuzumab, a humanized mAb targeting ErbB-2/HER2, a receptor frequently over expressed in breast cancer [62]. Trastuzumab (Herceptin®), is widely used now as a common treatment for patients with ErbB-2 overexpressing breast cancer [6365]. EGFR’s extracellular domain is similarly targeted using specific antibodies, with the aim of inhibiting ligand binding and accelerating receptor down-regulation, following antibody-directed clustering and aggregation [66]. In addition, recruitment of the patient’s immune system to the cancer cells, via the antibody’s Fc region, to promote antibody-dependent cell-mediated cytotoxicity, is considered another advantage of this approach [67]. Cetuximab (C225, Erbitux®) is a humanized mouse antibody that is approved for treatment of two clinical indications: patients with metastatic colorectal cancer (harboring wild-type KRAS, see below), or patients with advanced or recurrent head and neck cancer. The antibody has also shown some activity in NSCLC [68]. Panitumumab (Vectibix®) is a fully human EGFR antibody approved for treatment of advanced colorectal cancers that express wild-type KRAS and progressed during or after previous lines of therapy [69,70].

Because EGFRvIII exhibits a novel epitope at its extracellular domain, which is exclusive to cancer cells, antibodies specifically targeting this mutated form were generated and showed encouraging initial results in clinical trials [71]. Other therapies also utilize the epitope differences between EGFRvIII and its wild type counterpart. Active immunization with peptides based on the fusion junction of EGFRvIII was proven effective in animal models [72]. Additionally, a re-targeted oncolytic measles strain, that specifically identifies EGFRvIII, exhibited host cell specificity both in vitro and in animals, adding virus targeted therapy to the battery of future potential therapies [73].

Games of cat and mouse - EGFR secondary mutations

A unique opportunity to grasp the mutational micro-evolution of cancer progression has arisen through the treatment of NSCLC patients with gefitinib or erlotinib. Clinical trials have shown that only a relatively small portion of patients responded to the TKI treatment, but with impressive clinical improvement [24]. Further studies discovered that TKI responsiveness was dependent on point mutations or small deletions within the kinase domain. These mutations, while activating the kinase, also conferred sensitivity to treatment [52,74]. However, soon afterward, many of the responsive tumors relapsed under ongoing TKI treatment. Sequencing of the kinase domain from these tumors revealed a secondary mutation (T790M) that not only increases kinase activity, but grants TKI resistance as well [75,76]. Later, this phenomenon was repeated in mouse models establishing it as a secondary, resistance providing mutation [76], although it has been identified as a germ-line mutation in families with inherited cancer susceptibility as well [77]. This is an outstanding demonstration of cancer mechanisms relentlessly seeking for active signaling despite external perturbations.

Mutations downstream to EGFR

Apart from additional mutations that evolve to rescue EGFR activity and tumor progression, as seen in NSCLC, further mutations may preexist or appear in other components of signaling pathways, thus shifting the oncogenic addiction downstream, and rendering EGFR targeting insufficient. In glioblastomas, only a fraction of patients respond to EGFR TKI treatment. Thorough analysis revealed that some non-responsive tumors, although expressing the mutated EGFRvIII, displayed decreased expression of PTEN (phosphatase and tensin homolog) [78]. PTEN is a tumor suppressor (Fig. 1) that reverses the action of PI3K, transforming the second messenger PIP3, which is responsible for AKT activation, back to PIP2, therefore attenuating this signaling cascade. Tumors that lost PTEN expression often exhibit a constitutively active PI3K pathway, regardless of the status of EGFR. Indeed, reintroduction of PTEN into glioblastoma cells in vitro re-sensitized them to TKI treatment [78]. The PI3K pathway is mutationally altered in colorectal cancer (CRC) as well, in which additionally to PTEN deletion, PI3K activating mutations have been reported [79]. Additional downstream mutated proteins that confer resistance to EGFR-targeted therapy in colorectal cancer are KRAS and BRAF (see Fig. 1). Although EGFR is ubiquitously expressed in CRC, tests have shown that only patients expressing the wild type KRAS and BRAF, which are major mediators of the MAPK pathway, will benefit from anti-EGFR treatment [80,81]. Moreover, several reports concluded that occurrence of either EGFR or KRAS mutations are mutually exclusive in NSCLC [82], highlighting the apparent functional redundancy of these mutations.

The least explored route - recruitment of Heat Shock Protein (HSP) 90

HSP90 is a molecular chaperone that facilitates proper folding of specific client proteins in an ATP-dependent manner [83], and has a significant role in buffering genetic variation, contributing to evolutionary processes [84]. However, HSP90 also stabilizes viral kinases and mutated oncoproteins, such as v-SRC [85] and Bcr-Abl [86], revealing an inevitable darker side. While the constitutively active ErbB-2/HER2 is yet another HSP90 client [87], mutant forms of EGFR, probably due to their constitutively-active kinases, are dependent on the chaperoning function of HSP90 through direct interaction, which warrants their stability [8891]. Indeed HSP90 inhibition, using benzoquinoid ansamycins such as geldanamycin, reduces mutant EGFR levels and activity, suggesting an alternative EGFR inhibition strategy [92].

Concluding remarks

Evolution is usually referred to natural selection of species, with survival of the fittest to a changing environment. However, the same concept applies to cancer progression [93,94]: A tumor is composed of heterogeneous sub-clones, with each harboring slightly different sets of mutations [95]. Environmental stress, such as hypoxia, immune mediators and therapeutic interventions, selects the fittest clones for survival, thus pushing the tumor further to aggressiveness, and to finding new solutions for new pressures, such as in the case of secondary NSCLC mutations. Recently, a new generations of irreversible TKIs have been shown to exhibit activity against the secondary T790M mutation [96], thus raising the “arms race” to a new level. Time will tell whether new, tertiary resistant mutations will emerge, or whether this will drive tumors into switching to other kinases in their thrive for growth signals, such as ErbB-3 and MET, the receptor for the hepatocyte growth factor [97,98].

The discovery of the first oncogenes and tumor-suppressors helped in understanding the nature of cancer [99]. The acquisition of gain-of-function and loss-of-function mutations seems to similarly apply to the smaller scale of single proteins, such as EGFR: gain-of-function mutations affect the kinase domain, whereas regulatory safe-guards embedded within the EGFR, such as the ligand binding domain and the carboxyl tail, are the targets of loss-of-function mutations. Interestingly, specific cancer types choose different strategies.

Drug development, in its constant pursuit for maximizing clinical efficacy, while minimizing toxicity, led to a major effort concentrating on EGFR-targeted therapies. However, according to the lessons learnt from RAS mutations and PTEN deletions, in order to predict which patient will benefit from such treatments, the whole genomic and proteomic status of a tumor should be mapped and analyzed. With deep sequencing, microarray technology and high throughput proteomics, such an ambitious task may be plausible sooner than expected. Patient-specific drug combinations will have to consider not only the aberrant gene itself, but also common compensatory pathways to be simultaneously targeted, such as MET, AKT and ErbB-3, in the case of EGFR. Moreover, a third circle of inhibitors may be required, such as modifiers of the tumor’s stroma [100], blockers of angiogenesis [101], and HSP90 inhibitors. In lung tumors harboring mutant forms of EGFR, specific TKIs have already demonstrated superior efficacy and tolerability compared to conventional cytotoxic agents [102,103]. In the foreseeable future, similar approaches along with rationally designed combinations of targeted therapies, will hopefully achieve the goal also in brain and other tumors expressing mutant forms of EGFR.


Grant Support: Our laboratory is supported by research grants from the Goldhirsh Foundation, the National Cancer Institute (NIH), the Israel Science Foundation, the Israel Cancer Research Fund, the Prostate Cancer Research Foundation, the Dr. Miriam and Sheldon G. Adelson Medical Research Foundation and the German Research Foundation. Y.Y. is the incumbent of the Harold and Zelda Goldenberg Professorial Chair


Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.


1. Ushiro H, Cohen S. Identification of phosphotyrosine as a product of epidermal growth factor-activated protein kinase in A-431 cell membranes. J Biol Chem. 1980;255:8363–5. [PubMed]
2. Cohen S, Carpenter G, King L., Jr Epidermal growth factor-receptor-protein kinase interactions. Co-purification of receptor and epidermal growth factor-enhanced phosphorylation activity. J Biol Chem. 1980;255:4834–42. [PubMed]
3. Ogiso H, et al. Crystal structure of the complex of human epidermal growth factor and receptor extracellular domains. Cell. 2002;110:775–87. [PubMed]
4. Zhang X, Gureasko J, Shen K, Cole PA, Kuriyan J. An allosteric mechanism for activation of the kinase domain of epidermal growth factor receptor. Cell. 2006;125:1137–49. [PubMed]
5. Citri A, Yarden Y. EGF-ERBB signalling: towards the systems level. Nat Rev Mol Cell Biol. 2006;7:505–16. [PubMed]
6. Yarden Y. The EGFR family and its ligands in human cancer. signalling mechanisms and therapeutic opportunities. Eur J Cancer. 2001;37(Suppl 4):S3–8. [PubMed]
7. Casalini P, Iorio MV, Galmozzi E, Menard S. Role of HER receptors family in development and differentiation. J Cell Physiol. 2004;200:343–50. [PubMed]
8. Klapper LN, Glathe S, Vaisman N, Hynes NE, Andrews GC, Sela M, Yarden Y. The ErbB-2/HER2 oncoprotein of human carcinomas may function solely as a shared coreceptor for multiple stroma-derived growth factors. Proc Natl Acad Sci U S A. 1999;96:4995–5000. [PubMed]
9. Guy PM, Platko JV, Cantley LC, Cerione RA, Carraway KL., 3rd Insect cell-expressed p180erbB3 possesses an impaired tyrosine kinase activity. Proc Natl Acad Sci U S A. 1994;91:8132–6. [PubMed]
10. Yarden Y, Sliwkowski MX. Untangling the ErbB signalling network. Nat Rev Mol Cell Biol. 2001;2:127–37. [PubMed]
11. Ebner R, Derynck R. Epidermal growth factor and transforming growth factor-alpha: differential intracellular routing and processing of ligand-receptor complexes. Cell Regul. 1991;2:599–612. [PMC free article] [PubMed]
12. Sliwkowski MX, et al. Coexpression of erbB2 and erbB3 proteins reconstitutes a high affinity receptor for heregulin. J Biol Chem. 1994;269:14661–5. [PubMed]
13. Carraway KL, 3rd, Weber JL, Unger MJ, Ledesma J, Yu N, Gassmann M, Lai C. Neuregulin-2, a new ligand of ErbB3/ErbB4-receptor tyrosine kinases. Nature. 1997;387:512–6. [PubMed]
14. Harari D, Tzahar E, Romano J, Shelly M, Pierce JH, Andrews GC, Yarden Y. Neuregulin-4: a novel growth factor that acts through the ErbB-4 receptor tyrosine kinase. Oncogene. 1999;18:2681–9. [PubMed]
15. Kochupurakkal BS, et al. Epigen, the last ligand of ErbB receptors, reveals intricate relationships between affinity and mitogenicity. J Biol Chem. 2005;280:8503–12. [PubMed]
16. Normanno N, et al. Epidermal growth factor receptor (EGFR) signaling in cancer. Gene. 2006;366:2–16. [PubMed]
17. Barnes CJ, Kumar R. Epidermal growth factor receptor family tyrosine kinases as signal integrators and therapeutic targets. Cancer Metastasis Rev. 2003;22:301–7. [PubMed]
18. Tang P, Steck PA, Yung WK. The autocrine loop of TGF-alpha/EGFR and brain tumors. J Neurooncol. 1997;35:303–14. [PubMed]
19. Downward J, et al. Close similarity of epidermal growth factor receptor and v-erb-B oncogene protein sequences. Nature. 1984;307:521–7. [PubMed]
20. Ekstrand AJ, Sugawa N, James CD, Collins VP. Amplified and rearranged epidermal growth factor receptor genes in human glioblastomas reveal deletions of sequences encoding portions of the N- and/or C-terminal tails. Proc Natl Acad Sci U S A. 1992;89:4309–13. [PubMed]
21. Nagane M, Coufal F, Lin H, Bogler O, Cavenee WK, Huang HJ. A common mutant epidermal growth factor receptor confers enhanced tumorigenicity on human glioblastoma cells by increasing proliferation and reducing apoptosis. Cancer Res. 1996;56:5079–86. [PubMed]
22. Lee JC, et al. Epidermal growth factor receptor activation in glioblastoma through novel missense mutations in the extracellular domain. PLoS Med. 2006;3:e485. [PubMed]
23. Gotoh N, Tojo A, Hino M, Yazaki Y, Shibuya M. A highly conserved tyrosine residue at codon 845 within the kinase domain is not required for the transforming activity of human epidermal growth factor receptor. Biochem Biophys Res Commun. 1992;186:768–74. [PubMed]
24. Lynch TJ, et al. Activating mutations in the epidermal growth factor receptor underlying responsiveness of non-small-cell lung cancer to gefitinib. N Engl J Med. 2004;350:2129–39. [PubMed]
25. Nagahara H, et al. Somatic mutations of epidermal growth factor receptor in colorectal carcinoma. Clin Cancer Res. 2005;11:1368–71. [PubMed]
26. Douglas DA, et al. Novel mutations of epidermal growth factor receptor in localized prostate cancer. Front Biosci. 2006;11:2518–25. [PubMed]
27. Choi SH, Mendrola JM, Lemmon MA. EGF-independent activation of cell-surface EGF receptors harboring mutations found in gefitinib-sensitive lung cancer. Oncogene. 2007;26:1567–76. [PubMed]
28. Frederick L, Wang XY, Eley G, James CD. Diversity and frequency of epidermal growth factor receptor mutations in human glioblastomas. Cancer Res. 2000;60:1383–7. [PubMed]
29. Wood ER, et al. A unique structure for epidermal growth factor receptor bound to GW572016 (Lapatinib): relationships among protein conformation, inhibitor off-rate, and receptor activity in tumor cells. Cancer Res. 2004;64:6652–9. [PubMed]
30. Jura N, et al. Mechanism for activation of the EGF receptor catalytic domain by the juxtamembrane segment. Cell. 2009;137:1293–307. [PMC free article] [PubMed]
31. Landau M, Fleishman SJ, Ben-Tal N. A putative mechanism for downregulation of the catalytic activity of the EGF receptor via direct contact between its kinase and C-terminal domains. Structure. 2004;12:2265–75. [PubMed]
32. Ozer BH, Wiepz GJ, Bertics PJ. Activity and cellular localization of an oncogenic glioblastoma multiforme-associated EGF receptor mutant possessing a duplicated kinase domain. Oncogene. 2010;29:855–64. [PMC free article] [PubMed]
33. Sugawa N, Ekstrand AJ, James CD, Collins VP. Identical splicing of aberrant epidermal growth factor receptor transcripts from amplified rearranged genes in human glioblastomas. Proc Natl Acad Sci U S A. 1990;87:8602–6. [PubMed]
34. Wong AJ, Ruppert JM, Bigner SH, Grzeschik CH, Humphrey PA, Bigner DS, Vogelstein B. Structural alterations of the epidermal growth factor receptor gene in human gliomas. Proc Natl Acad Sci U S A. 1992;89:2965–9. [PubMed]
35. Moscatello DK, et al. Frequent expression of a mutant epidermal growth factor receptor in multiple human tumors. Cancer Res. 1995;55:5536–9. [PubMed]
36. Ji H, et al. Epidermal growth factor receptor variant III mutations in lung tumorigenesis and sensitivity to tyrosine kinase inhibitors. Proc Natl Acad Sci U S A. 2006;103:7817–22. [PubMed]
37. Wikstrand CJ, McLendon RE, Friedman AH, Bigner DD. Cell surface localization and density of the tumor-associated variant of the epidermal growth factor receptor, EGFRvIII. Cancer Res. 1997;57:4130–40. [PubMed]
38. Moscatello DK, Montgomery RB, Sundareshan P, McDanel H, Wong MY, Wong AJ. Transformational and altered signal transduction by a naturally occurring mutant EGF receptor. Oncogene. 1996;13:85–96. [PubMed]
39. Batra SK, Castelino-Prabhu S, Wikstrand CJ, Zhu X, Humphrey PA, Friedman HS, Bigner DD. Epidermal growth factor ligand-independent, unregulated, cell-transforming potential of a naturally occurring human mutant EGFRvIII gene. Cell Growth Differ. 1995;6:1251–9. [PubMed]
40. Al-Nedawi K, Meehan B, Micallef J, Lhotak V, May L, Guha A, Rak J. Intercellular transfer of the oncogenic receptor EGFRvIII by microvesicles derived from tumour cells. Nat Cell Biol. 2008;10:619–24. [PubMed]
41. Sonobe M, Manabe T, Wada H, Tanaka F. Mutations in the epidermal growth factor receptor gene are linked to smoking-independent, lung adenocarcinoma. Br J Cancer. 2005;93:355–63. [PMC free article] [PubMed]
42. Shigematsu H, et al. Clinical and biological features associated with epidermal growth factor receptor gene mutations in lung cancers. J Natl Cancer Inst. 2005;97:339–46. [PubMed]
43. Shigematsu H, Gazdar AF. Somatic mutations of epidermal growth factor receptor signaling pathway in lung cancers. Int J Cancer. 2006;118:257–62. [PubMed]
44. Landau M, Ben-Tal N. Dynamic equilibrium between multiple active and inactive conformations explains regulation and oncogenic mutations in ErbB receptors. Biochim Biophys Acta. 2008;1785:12–31. [PubMed]
45. Chen YR, Fu YN, Lin CH, Yang ST, Hu SF, Chen YT, Tsai SF, Huang SF. Distinctive activation patterns in constitutively active and gefitinib-sensitive EGFR mutants. Oncogene. 2006;25:1205–15. [PubMed]
46. Moscatello DK, Holgado-Madruga M, Emlet DR, Montgomery RB, Wong AJ. Constitutive activation of phosphatidylinositol 3-kinase by a naturally occurring mutant epidermal growth factor receptor. J Biol Chem. 1998;273:200–6. [PubMed]
47. Li B, Yuan M, Kim IA, Chang CM, Bernhard EJ, Shu HK. Mutant epidermal growth factor receptor displays increased signaling through the phosphatidylinositol-3 kinase/AKT pathway and promotes radioresistance in cells of astrocytic origin. Oncogene. 2004;23:4594–602. [PubMed]
48. Huang PH, Mukasa A, Bonavia R, Flynn RA, Brewer ZE, Cavenee WK, Furnari FB, White FM. Quantitative analysis of EGFRvIII cellular signaling networks reveals a combinatorial therapeutic strategy for glioblastoma. Proc Natl Acad Sci U S A. 2007;104:12867–72. [PubMed]
49. Pedersen MW, et al. Analysis of the epidermal growth factor receptor specific transcriptome: effect of receptor expression level and an activating mutation. J Cell Biochem. 2005;96:412–27. [PubMed]
50. Shtiegman K, et al. Defective ubiquitinylation of EGFR mutants of lung cancer confers prolonged signaling. Oncogene. 2007;26:6968–78. [PubMed]
51. Cai CQ, et al. Epidermal growth factor receptor activation in prostate cancer by three novel missense mutations. Oncogene. 2008;27:3201–10. [PubMed]
52. Carey KD, et al. Kinetic analysis of epidermal growth factor receptor somatic mutant proteins shows increased sensitivity to the epidermal growth factor receptor tyrosine kinase inhibitor, erlotinib. Cancer Res. 2006;66:8163–71. [PubMed]
53. Weinstein IB. Disorders in cell circuitry during multistage carcinogenesis: the role of homeostasis. Carcinogenesis. 2000;21:857–64. [PubMed]
54. Sharma SV, Fischbach MA, Haber DA, Settleman J. “Oncogenic shock”: explaining oncogene addiction through differential signal attenuation. Clin Cancer Res. 2006;12:4392s–4395s. [PubMed]
55. Levitzki A, Mishani E. Tyrphostins and other tyrosine kinase inhibitors. Annu Rev Biochem. 2006;75:93–109. [PubMed]
56. Perez-Soler R. The role of erlotinib (Tarceva, OSI 774) in the treatment of non-small cell lung cancer. Clin Cancer Res. 2004;10:4238s–4240s. [PubMed]
57. Fukuoka M, et al. Multi-institutional randomized phase II trial of gefitinib for previously treated patients with advanced non-small-cell lung cancer (The IDEAL 1 Trial) [corrected] J Clin Oncol. 2003;21:2237–46. [PubMed]
58. Moore MJ, et al. Erlotinib plus gemcitabine compared with gemcitabine alone in patients with advanced pancreatic cancer: a phase III trial of the National Cancer Institute of Canada Clinical Trials Group. J Clin Oncol. 2007;25:1960–6. [PubMed]
59. Fountzilas G, et al. Gemcitabine combined with gefitinib in patients with inoperable or metastatic pancreatic cancer: a phase II Study of the Hellenic Cooperative Oncology Group with biomarker evaluation. Cancer Invest. 2008;26:784–93. [PubMed]
60. Geyer CE, et al. Lapatinib plus capecitabine for HER2-positive advanced breast cancer. N Engl J Med. 2006;355:2733–43. [PubMed]
61. Blackwell KL, et al. Randomized study of Lapatinib alone or in combination with trastuzumab in women with ErbB2-positive, trastuzumab-refractory metastatic breast cancer. J Clin Oncol. 2010;28:1124–30. [PubMed]
62. Cobleigh MA, et al. Multinational study of the efficacy and safety of humanized anti-HER2 monoclonal antibody in women who have HER2-overexpressing metastatic breast cancer that has progressed after chemotherapy for metastatic disease. J Clin Oncol. 1999;17:2639–48. [PubMed]
63. Slamon DJ, et al. Use of chemotherapy plus a monoclonal antibody against HER2 for metastatic breast cancer that overexpresses HER2. N Engl J Med. 2001;344:783–92. [PubMed]
64. Romond EH, et al. Trastuzumab plus adjuvant chemotherapy for operable HER2-positive breast cancer. N Engl J Med. 2005;353:1673–84. [PubMed]
65. Piccart-Gebhart MJ, et al. Trastuzumab after adjuvant chemotherapy in HER2-positive breast cancer. N Engl J Med. 2005;353:1659–72. [PubMed]
66. Ben-Kasus T, Schechter B, Sela M, Yarden Y. Cancer therapeutic antibodies come of age: targeting minimal residual disease. Mol Oncol. 2007;1:42–54. [PubMed]
67. Clynes RA, Towers TL, Presta LG, Ravetch JV. Inhibitory Fc receptors modulate in vivo cytoxicity against tumor targets. Nat Med. 2000;6:443–6. [PubMed]
68. Pirker R, et al. Cetuximab plus chemotherapy in patients with advanced non-small-cell lung cancer (FLEX): an open-label randomised phase III trial. Lancet. 2009;373:1525–31. [PubMed]
69. Amado RG, et al. Wild-type KRAS is required for panitumumab efficacy in patients with metastatic colorectal cancer. J Clin Oncol. 2008;26:1626–34. [PubMed]
70. Peeters M, Balfour J, Arnold D. Review article: panitumumab - a fully human anti-EGFR monoclonal antibody for treatment of metastatic colorectal cancer. Aliment Pharmacol Ther 2008 [PubMed]
71. Scott AM, et al. A phase I clinical trial with monoclonal antibody ch806 targeting transitional state and mutant epidermal growth factor receptors. Proc Natl Acad Sci U S A. 2007;104:4071–6. [PubMed]
72. Heimberger AB, et al. Epidermal growth factor receptor VIII peptide vaccination is efficacious against established intracerebral tumors. Clin Cancer Res. 2003;9:4247–54. [PubMed]
73. Allen C, et al. Retargeted oncolytic measles strains entering via the EGFRvIII receptor maintain significant antitumor activity against gliomas with increased tumor specificity. Cancer Res. 2006;66:11840–50. [PubMed]
74. Yun CH, Boggon TJ, Li Y, Woo MS, Greulich H, Meyerson M, Eck MJ. Structures of lung cancer-derived EGFR mutants and inhibitor complexes: mechanism of activation and insights into differential inhibitor sensitivity. Cancer Cell. 2007;11:217–27. [PMC free article] [PubMed]
75. Kobayashi S, et al. EGFR mutation and resistance of non-small-cell lung cancer to gefitinib. N Engl J Med. 2005;352:786–92. [PubMed]
76. Pao W, Miller VA, Politi KA, Riely GJ, Somwar R, Zakowski MF, Kris MG, Varmus H. Acquired resistance of lung adenocarcinomas to gefitinib or erlotinib is associated with a second mutation in the EGFR kinase domain. PLoS Med. 2005;2:e73. [PubMed]
77. Bell DW, et al. Inherited susceptibility to lung cancer may be associated with the T790M drug resistance mutation in EGFR. Nat Genet. 2005;37:1315–6. [PubMed]
78. Mellinghoff IK, et al. Molecular determinants of the response of glioblastomas to EGFR kinase inhibitors. N Engl J Med. 2005;353:2012–24. [PubMed]
79. Jhawer M, et al. PIK3CA mutation/PTEN expression status predicts response of colon cancer cells to the epidermal growth factor receptor inhibitor cetuximab. Cancer Res. 2008;68:1953–61. [PMC free article] [PubMed]
80. Lievre A, et al. KRAS mutation status is predictive of response to cetuximab therapy in colorectal cancer. Cancer Res. 2006;66:3992–5. [PubMed]
81. Laurent-Puig P, et al. Analysis of PTEN, BRAF, and EGFR status in determining benefit from cetuximab therapy in wild-type KRAS metastatic colon cancer. J Clin Oncol. 2009;27:5924–30. [PubMed]
82. Kosaka T, Yatabe Y, Endoh H, Kuwano H, Takahashi T, Mitsudomi T. Mutations of the epidermal growth factor receptor gene in lung cancer: biological and clinical implications. Cancer Res. 2004;64:8919–23. [PubMed]
83. Pearl LH, Prodromou C. Structure and mechanism of the Hsp90 molecular chaperone machinery. Annu Rev Biochem. 2006;75:271–94. [PubMed]
84. Sangster TA, Lindquist S, Queitsch C. Under cover: causes, effects and implications of Hsp90-mediated genetic capacitance. Bioessays. 2004;26:348–62. [PubMed]
85. Whitesell L, Mimnaugh EG, De Costa B, Myers CE, Neckers LM. Inhibition of heat shock protein HSP90-pp60v-src heteroprotein complex formation by benzoquinone ansamycins: essential role for stress proteins in oncogenic transformation. Proc Natl Acad Sci U S A. 1994;91:8324–8. [PubMed]
86. An WG, Schulte TW, Neckers LM. The heat shock protein 90 antagonist geldanamycin alters chaperone association with p210bcr-abl and v-src proteins before their degradation by the proteasome. Cell Growth Differ. 2000;11:355–60. [PubMed]
87. Zsebik B, Citri A, Isola J, Yarden Y, Szollosi J, Vereb G. Hsp90 inhibitor 17-AAG reduces ErbB2 levels and inhibits proliferation of the trastuzumab resistant breast tumor cell line JIMT-1. Immunol Lett. 2006;104:146–55. [PubMed]
88. Shimamura T, Lowell AM, Engelman JA, Shapiro GI. Epidermal growth factor receptors harboring kinase domain mutations associate with the heat shock protein 90 chaperone and are destabilized following exposure to geldanamycins. Cancer Res. 2005;65:6401–8. [PubMed]
89. Shimamura T, et al. Hsp90 inhibition suppresses mutant EGFR-T790M signaling and overcomes kinase inhibitor resistance. Cancer Res. 2008;68:5827–38. [PMC free article] [PubMed]
90. Lavictoire SJ, Parolin DA, Klimowicz AC, Kelly JF, Lorimer IA. Interaction of Hsp90 with the nascent form of the mutant epidermal growth factor receptor EGFRvIII. J Biol Chem. 2003;278:5292–9. [PubMed]
91. Yang S, Qu S, Perez-Tores M, Sawai A, Rosen N, Solit DB, Arteaga CL. Association with HSP90 inhibits Cbl-mediated down-regulation of mutant epidermal growth factor receptors. Cancer Res. 2006;66:6990–7. [PubMed]
92. Biamonte MA, Van de Water R, Arndt JW, Scannevin RH, Perret D, Lee WC. Heat shock protein 90: inhibitors in clinical trials. J Med Chem. 2010;53:3–17. [PubMed]
93. Nowell PC. The clonal evolution of tumor cell populations. Science. 1976;194:23–8. [PubMed]
94. Merlo LM, Pepper JW, Reid BJ, Maley CC. Cancer as an evolutionary and ecological process. Nat Rev Cancer. 2006;6:924–35. [PubMed]
95. Braakhuis BJ, Leemans CR, Brakenhoff RH. Expanding fields of genetically altered cells in head and neck squamous carcinogenesis. Semin Cancer Biol. 2005;15:113–20. [PubMed]
96. Zhou W, et al. Novel mutant-selective EGFR kinase inhibitors against EGFR T790M. Nature. 2009;462:1070–4. [PMC free article] [PubMed]
97. Sergina NV, Rausch M, Wang D, Blair J, Hann B, Shokat KM, Moasser MM. Escape from HER-family tyrosine kinase inhibitor therapy by the kinase-inactive HER3. Nature. 2007;445:437–41. [PMC free article] [PubMed]
98. Engelman JA, et al. MET amplification leads to gefitinib resistance in lung cancer by activating ERBB3 signaling. Science. 2007;316:1039–43. [PubMed]
99. Murphree AL, Benedict WF. Retinoblastoma: clues to human oncogenesis. Science. 1984;223:1028–33. [PubMed]
100. Sheffer Y, et al. Inhibition of fibroblast to myofibroblast transition by halofuginone contributes to the chemotherapy-mediated antitumoral effect. Mol Cancer Ther. 2007;6:570–7. [PubMed]
101. Folkman J. Angiogenesis: an organizing principle for drug discovery? Nat Rev Drug Discov. 2007;6:273–86. [PubMed]
102. Sekine I, et al. Quality of life and disease-related symptoms in previously treated Japanese patients with non-small-cell lung cancer: results of a randomized phase III study (V-15-32) of gefitinib versus docetaxel. Ann Oncol. 2009;20:1483–8. [PubMed]
103. Mok TS, et al. Gefitinib or carboplatin-paclitaxel in pulmonary adenocarcinoma. N Engl J Med. 2009;361:947–57. [PubMed]
104. Humphrey PA, et al. Deletion-mutant epidermal growth factor receptor in human gliomas: effects of type II mutation on receptor function. Biochem Biophys Res Commun. 1991;178:1413–20. [PubMed]
105. Paez JG, et al. EGFR mutations in lung cancer: correlation with clinical response to gefitinib therapy. Science. 2004;304:1497–500. [PubMed]
106. Greulich H, et al. Oncogenic transformation by inhibitor-sensitive and -resistant EGFR mutants. PLoS Med. 2005;2:e313. [PubMed]