Hindawi Publishing Corporation
Chemotherapy Research and Practice
Volume 2012, Article ID 817297, 9 pages
Mechanismsof Resistanceto EpidermalGrowthFactor
to OvercomeResistanceinNSCLC Patients
Division of Hematology/Oncology, Department of Medicine, USCF Helen Diller Family Comprehensive Cancer Center,
University of California, San Francisco, San Francisco, CA 94158, USA
Correspondence should be addressed to Trever G. Bivona, email@example.com
Received 12 April 2012; Accepted 30 July 2012
Academic Editor: Nabil F. Saba
Copyright © 2012 L. Lin and T. G. Bivona. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
The epidermal growth factor receptor (EGFR) is a well-characterized oncogene that is frequently activated by somatic kinase
domain mutations in non-small cell lung cancer (NSCLC). EGFR TKIs are effective therapies for NSCLC patients whose tumors
harbor an EGFR activating mutation. However, EGFR TKI treatment is not curative in patients because of both primary and
secondary treatment resistance. Studies over the last decade have identified mechanisms that drive primary and secondary
resistance to EGFR TKI treatment. The elucidation of mechanisms of resistance to EGFR TKI treatment provides a basis for
the development of therapeutic strategies to overcome resistance and enhance outcomes in NSCLC patients. In this paper, we
summarize the mechanisms of resistance to EGFR TKIs that have been identified to date and discusses potential therapeutic
strategies to overcome EGFR TKI resistance in NSCLC patients.
Lung cancer is the leading cause of cancer mortality in the
United States and worldwide, accounting for 28% of cancer-
related deaths in males and 26% of cancer-related deaths
in females [1, 2]. Most lung cancer patients present with
advanced stage disease, for which conventional chemother-
apies patients are only modestly effective. Thus, the 5-year-
oncogenes that encode activated signaling molecules that
drive cellular proliferation and promote tumor growth has
led to the development of more effective and less toxic
targeted drugs for lung cancer patients. Systemic therapies
that act against specific activated oncogenes in lung cancers
have the potential for improving outcomes for lung cancer
patients in an unprecedented manner. Yet, a significant
challenge that must be overcome in order to realize the full
potential of targeted cancer therapy in lung cancer patients
is resistance to treatment with an oncogene inhibitor as
The epidermal growth factor receptor (EGFR) is a well-
characterized mutated oncogene in non-small cell lung can-
cer (NSCLC) that is found in ∼10–20% of cases in western
countries and is associated predominantly with adenocar-
cinoma histology. EGFR-mutated tumors are dependent to
EGFR signaling for their proliferation and survival [4–
7]. In lung cancer patients, EGFR mutations are generally
exclusive with KRAS and BRAF mutations, and tumors
with either KRAS (15–25%) or BRAF (2-3%) mutations are
relatively insensitive to EGFR TKIs [8, 9]. The most common
activating mutations (∼90%) are in-frame deletions in exon
19 of EGFR and a missense mutation at 858 in exon 21
of EGFR resulting in an arginine to leucine substitution
(L858R) . Therapeutic agents targeting the EGFR signal-
ing pathway, including two EGFR kinase inhibitors gefitinib
and erlotinib, are clinically effective in treating lung cancer
Despite the dramatic efficacy of EGFR TKIs in NSCLC
patients with EGFR activating mutations, unfortunately, de
novo resistance to TKIs is observed and virtually all patients
who initially respond will ultimately develop acquired
2Chemotherapy Research and Practice
resistance.In this paper, we focuson the mechanisms of both
de novo resistance (lack of an initial response to therapy)
and acquired resistance (resistance that develops following
an initial response to therapy) to EGFR TKIs. We also
discuss potential strategies to overcome resistance in lung
cancer patients. It is currently not known whether acquired
resistance occurs through clonal selection of resistant tumor
Approaches such as lineage tracing or next generation deep
sequencing at the single-cell level could be used to address
this unresolved issue.
2.De Novo Resistance to EGFRTKIs
Non-small cell lung cancers harboring an EGFR activating
mutation can show primary resistance to EGFR TKI ther-
apy. Among patients with an EGFR activating mutation,
regressions when treated with an EGFR TKI [15–17]. Thus,
approximately 30% of patients with an EGFR activating
mutation experience de novo resistance to EGFR TKIs.
Two general mechanisms of de novo resistance to EGFR
TKI treatment in EGFR mutant NSCLC patients have been
described to date: (1) secondary alterations in EGFR that
prevent inhibition of EGFR by an EGFR TKI (drug resistant
can co-occur with an EGFR activating mutation in EGFR
mutant NSCLC cells.
2.1. Drug Resistant EGFR Mutation. NSCLCs harboring a
small insertion or duplication in exon 20 observed in ∼5%
of NSCLCs are less sensitive to EGFR TKIs compared to the
exon 19 deletion mutants and L858R mutants in vitro ,
as well as in patients . Similarly, patients harboring an
EGFR T790M mutation in exon 20 are also resistant to EGFR
TKI treatment [20–22]. Interestingly, the EGFR T790M
mutation can also be found at low frequency (approximately
0.54% of never smokers with lung cancer) in the germ line of
patients. The presence of a germline EGFR T790M mutation
may be associated with increased risk of developing lung
cancer [23–25]. In pretreated patients harboring a T790M
a prolonged progression-free survival to erlotinib treatment.
The data suggest that low BRCA1 level may neutralize the
negative effects of the EGFR T790M mutation on erlotinib
sensitivity and that high BRCA1 expression may lead to
de novo EGFR TKI resistance potentially through increased
DNA damage repair capacity . In addition to EGFR
T790M, primary EGFR TKI resistance may also be due to
other secondary mutations in EGFR (e.g., D761Y) that occur
in cis with an activating EGFR kinase domain mutation (e.g.,
2.2. Other Genetic Alternations with EGFR Mutations. The
presence of other genetic alterations together with EGFR
activating mutations in lung cancer cells could lead to EGFR
TKI resistance by promoting cell survival in the face of
EGFR TKI resistance that have been reported to date are
summarized in the following discussion.
2.2.1. Activation of Phosphoinositide-3-Kinase(PI3K)/AKT
Signaling. Loss of PTEN expression in EGFR mutant cells
has been associated with decreased sensitivity to EGFR TKIs
by activation of PI3K-AKT signaling, the impairment of the
ligand-induced ubiquitination, and degradation of activated
EGFR [28, 29]. Moreover, PIK3CA, the p110alpha catalytic
subunit of PI3K, was found to be mutated in approximately
1.3% of Japanese lung cancer patient with EGFR mutations
versus 2.1% in patients without EGFR mutations . In
addition, the constitutively activated PI3K (E545K) has been
shown to confer resistance of EGFR TKI in vitro .
2.2.2. Involvement of IGF1R Signaling. The IGF1R signal-
ing pathway has been implicated in EGFR TKI resistance
EGFR activating mutations. For example, cotreatment of
cell cycle arrest, while single agent of either inhibitor alone
only induce cell cycle arrest in some EGFR mutant NSCLC
cells . Moreover, Sharma et al. discovered that EGFR
mutant lung cancer cell lines persisting after EGFR TKI
treatment were enriched for a drug-tolerant subpopulation
that may have existed prior to treatment. This drug-tolerant
subpopulation of cells showed a distinct chromatin state that
2.2.3. Activation of NFκB Signaling. NFκB signaling has
been broadly associated with inflammation and cancer .
as a new mechanism of de novo resistance to erlotinib
treatment. This group used a high throughput unbiased
an exon 19 deletion in EGFR and are insensitive to EGFR
TKI treatment to define genetic modifiers that contribute to
de novo EGFR TKI resistance. Of the 36 shRNAs recovered
FAS death receptor. Prior work had shown that CD95/FAS
can, in some contexts, function upstream of NFκB to
promote cell survival and tumor growth. The authors found
that genetic or pharmacologic inhibition of NFκB signaling
increased sensitivity to erlotinib but not to chemotherapy in
several models of EGFR mutant lung cancer. Intriguingly,
low expression of the NFκB inhibitor IκB was predictive of
a poor clinical outcome in patients treated with erlotinib
without a T790M mutation. Importantly, IκB status was
not predictive of outcomes in EGFR mutant lung cancer
patients treated with surgery or chemotherapy, indicating
NFκB signaling is specific biomarker of EGFR TKI response
in this patient population [35, 36] (Figure 1). These results
suggest that hyperactivation of NFκB signaling may cause
de novo resistance to EGFR TKI treatment in EGFR mutant
lung cancer patients.
Chemotherapy Research and Practice3
Proliferation and survival
increase IκB level
Figure 1: Mechanisms of resistance to EGFR TKIs and multiple strategies to overcome resistance in EGFR mutant lung cancer. EGFR
signals through the RAS/RAF/MEK/ERK and PI3K/AKT pathways to promote cellular proliferation and survival. Crosstalk of other receptor
tyrosine kinase confers resistance to EGFR TKIs by activation of both MAPK and AKT signaling. The FAS/NFκB signaling arm downstream
of FAS death receptor also contributes to resistance to EGFR TKIs. Available targeted agents that act against pathways that drive EGFR TKI
resistance and that may overcome resistance to EGFR TKIs in appropriately selected lung cancer patients are shown.
3.AcquiredResistance to EGFRTKIs
Among NSCLC patients with activating EGFR mutation,
approximately 70% will experience significant tumor regres-
sions when treated with an EGFR TKI [15–17]. However,
the vast majority of patients that initially respond to
EGFR TKI treatment develop acquired EGFR TKI resistance
after a median of 10–14 months on EGFR-TKI treatment
[11, 14, 37].
3.1. Second-Site Mutations. Approximately 50% of patients
with EGFR mutant lung cancers who develop acquired
resistance to EGFR TKIs have a second-site mutation T790M
in the threonine gatekeeper residue that coexists with a
primary EGFR activating mutation [38, 39]. The T790M
mutation occurs at a conserved threonine residue located
near the kinase active site that is found in many kinases
and is often referred to as the “gatekeeper mutation”.
Gatekeeper mutations have been found in many kinase-
driven tumors that develop resistance to kinase inhibitor
treatment (e.g., CML patients treated with imatinib that
develop the T315I resistance mutation in BCR-ABL). Two
potential mechanisms could explain how the EGFR T790M
mutation confers EGFR TKI resistance. One possibility is
that the T790M mutation could lead to altered drug binding
in the ATP pocket of EGFR in a manner analogous to the
effects of the T315I mutation in the ABL kinase in the
context of imatinib resistance . The other possibility
is that the presence of the EGFR T790M mutation could
increase the affinity of the EGFR-L858R for ATP and thus
4 Chemotherapy Research and Practice
reduce the potency of an ATP-competitive kinase inhibitor
. Alternative pharmacological strategies targeting EGFR
T790M may be therapeutically efficacious to treat patients
with acquired resistance to EGFR TKIs and an EGFR T790M
The EGFR T790M mutant exhibits synergistic kinase
activity and transformation potential when coexisting with
an EGFR activating mutation in preclinical models [42, 43].
Interestingly, the subclonal populations of EGFR mutant
tumor cells with and without the EGFR T790M allele may
coexist in an EGFR mutant lung cancer with acquired
EGFR TKI resistance. This clonal heterogeneity may explain
both the “flare” phenomenon (rapid tumor regrowth upon
withdrawal of an EGFR TKI) observed in EGFR mutant lung
cancer patients upon discontinuation of an EGFR TKI and
also the finding that patients may respond to subsequent
EGFR TKI treatment after initial discontinuation of therapy.
[44–47]. The detailed biological mechanisms underlying
these clinical phenomena are unknown.
In addition to the EGFR T790M mutation, there are
three other second-site mutations in EGFR that have been
associated with acquired EGFR TKI resistance: T854A in
exon21 , L747S , and D761Y , both in the
exon19. Similar to the EGFR T790M mutation, alteration
of the drug contact residue T854 to a smaller hydrophobic
alanine may increase the size of the selectivity pocket and
negatively impact erlotinib binding. L747S is thought to
shift the equilibrium towards the active conformation of the
receptor, while D761Y may affect the catalytic cleft of the
receptor. Both T854 and D761 were identified in laboratory
models of erlotinib resistance in addition to clinical samples
3.2. MET Amplification. Amplification of MET, a receptor
tyrosine kinase, was detected in up to 20% of lung cancer
specimens that developed acquired resistance to gefitinib
or erlotinib. Although MET amplification can coexist with
the EGFR T790M mutation, approximately 60% of MET
amplification is independent of T790M mutation [51, 52].
MET amplification was originally identified in a laboratory-
model of gefitinib resistance using HCC827 human EGFR
mutant NSCLC cells. In this model, cells with EGFR TKI
resistance relied on MET signaling to activate AKT through
ERBB3-mediated activation of PI3K in the presence of EGFR
TKIs . In addition, the MET ligand hepatocyte growth
factor (HGF) induced gefitinib resistance through activation
of MET-PI3K signaling . MET amplification was also
observed at a low frequency in EGFR mutant lung cancers
in patients prior to treatment and was associated with the
development of acquired resistance to EGFR TKIs .
Together the data suggest that EGFR TKI treatment may
acquisition of EGFR TKI resistance (Figure 1).
3.3. Other Potential Mechanisms. EGFR T790M and MET
amplification account for ∼60% of acquired resistance
to EGFR TKIs. Other mechanisms of resistance that are
operative in the remaining ∼40% of tumors with acquired
resistance to EGFR TKIs are under active investigation.
3.3.1. PI3KCA Mutation. Recently, mutations in PIK3CA
were identified in ∼5% of EGFR mutant lung cancers that
developed acquired EGFR TKI resistance. These clinical
data were consistent with earlier data demonstrating that
introduction of an activated PIK3CA mutant into the EGFR
mutant cell line HCC827 confers resistance to gefitinib [31,
55]. These findings suggest that lung cancer patients with
both EGFR and PIK3CA mutations could be considered
for combination therapy with an EGFR TKI and a PI3K
3.3.2. EMT and Histological Transformation. The epithelial
to mesenchymal transition (EMT) has been considered as
a general biological switch rendering NSCLC sensitive or
insensitive to EGFR inhibition [56, 57]. Increased expression
of E-cadherin, an epithelial marker, has been associated with
clinical activity of EGFR inhibitors in NSCLC patients [58,
59]. EMT has been also associated with acquired resistance
It is not known if mesenchymal-like cells in the acquired
resistant tumors are exist prior to therapy or are induced
upon drug treatment.
Sequist et al. unexpectedly found a histological transfor-
mation from NSCLC into small cell lung cancer (SCLC) in
14% of EGFR mutant lung cancer patients (5 of 37) with
acquired EGFR TKI resistance. Importantly, transformation
to SCLC was associated with a response to treatment with
standard SCLC chemotherapy. Three independent studies
have identified three cases of SCLC harboring an EGFR
mutation [62–64]. Further investigation is necessary to clar-
ify the role and genesis of these histological transformations
in EGFR inhibitor resistance in lung cancer patients.
3.3.3. Activation of AXL. Recently, three groups indepen-
kinase confers acquired resistance to erlotinib in both cell
culture and tumor xenograft models of EGFR mutant lung
cancer. Activation of AXL occurred through overexpression
as well as through upregulation of its ligand GAS6 in the
setting of EGFR TKI resistance in EGFR-mutant NSCLCs.
Genetically or pharmacologically inhibiting AXL restored
erlotinib sensitivity both in vitro and in vivo. Moreover,
forced expression of AXL in EGFR mutant lung cancer
cell lines that are sensitive to erlotinib induced erlotinib
resistance through the kinase activity of AXL. Interestingly,
upregulation of AXL was associated with the development
of an epithelial to mesenchymal transition (EMT) in EGFR
mutant tumors with acquired erlotinib resistance. By com-
patients, approximately 20% of the EGFR TKI resistance
cases showed increased AXL expression. This observation
provides strong rationale for the development and testing
of AXL kinase inhibitors for clinical use in EGFR-mutant
Chemotherapy Research and Practice5
NSCLC patients to either prevent or overcome acquired
EGFR TKI resistance  (Figure 1).
3.3.4. Other Mechanisms: IGF1R and PTEN Pathways.
Increased IGF1R signaling through the loss of inhibitory
IGF-binding proteins has also been associated with acquired
EGFR TKI resistance in a laboratory model using a lung
squamous cell line expressing high-level of wild-type EGFR
. Loss or reduction of the tumor suppressor PTEN
has been associated with acquired EGFR TKI resistance in
PTEN loss have not been yet validated as mechanisms of
acquired EGFR TKI resistance in clinical specimens.
the EGFR-directed antibody cetuximab is also an effective
clinical therapy for patients with NSCLC, colorectal, and
head and neck cancers. Some NSCLC cells that are sensitive
to EGFR TKIs are sensitive to cetuximab as well. EGFR
mutant HCC827 cells with acquired resistance to cetuximab
were generated and shown to harbor amplification of ERBB2
or disruption of ERBB2/ERBB3 heterodimerization restored
cetuximab sensitivity in vitro and in vivo in these models
To date, the biological basis underlying acquired EGFR
TKI resistance is unknown in ∼30% of patients. Some
mechanisms of resistance that have been identified using
laboratory models have not been validated in patients with
acquired resistance, indicating the limitation of these labo-
ratory models of acquired EGFR TKI resistance. Integrated
approaches to study acquired EGFR TKI resistance using
genetically engineered mouse models (GEMMs) of EGFR
mutant lung cancer combined with patient derived cell lines
and the analysis of clinical specimens hold promise for
deciphering the remaining unknown mechanisms of EGFR
TKI resistance .
4.Overcoming Resistance to EGFRTKIs
4.1. De Novo Resistance
4.1.1. Novel EGFR TKIs. For lung cancer patients harboring
a secondary mutation in EGFR that abrogates EGFR TKI
affinity or binding, such as exon 20 insertion, duplication
TKIs are needed to more effectively target mutant EGFR.
The second-generation EGFR TKI PF00299804 (Pfizer) has
been shown to induce partial response in one patient with
an EGFR exon 20 insertion . Moreover, the second-
generation irreversible EGFR inhibitors were shown in
preclinical models to be more potent targeting T790M
mutation than gefitinib or erlotinib . Emerging EGFR
TKIs that exhibit increased potency against an activated
EGFR mutant oncoprotein may open a therapeutic window
for patient with rare mutations of EGFR.
4.1.2. Polytherapies. For patients harboring other genetic
alterations along with an EGFR activating mutation, poly-
therapies could be pursued. For example, NFκB signaling
can decrease erlotinib sensitivity in NSCLC cells with EGFR
activating mutation, leading to de novo resistance to EGFR
TKI treatment . Compounds such as MLN0415 and
BMS345541 that target IKK and IKK-related kinases (e.g.,
IKKβ) that activate NFκB  may overcome de novo resis-
tance to EGFR TKI treatment. Similarly, compounds such as
Nedd8 activating enzyme (NAE) inhibitor MLN4924 or the
of the NFκB inhibitor IκB [74, 75] may increase responses to
EGFR TKI treatment.
EGFR mutant lung cancers with genetic alterations that
activate the PI3K-AKT signaling pathway or IGF1R signaling
may benefit from treatment with PI3K or AKT inhibitors
or an IGF1R antibody, respectively, in combination with an
that induction of the proapoptotic protein Bim is essential
for apoptosis triggered by EGFR TKI treatment. Moreover,
a polymorphism in BIM that generates a dysfunctional
form of the protein that leads to intrinsic EGFR TKI
resistance in EGFR mutant NSCLC cell lines was recently
described. Together, the data suggest that adding a BCL-2
inhibitor (ABT-737) to EGFR TKI therapy could enhance
responses in patients, particularly those patients with a BIM
4.2. Acquired Resistance
4.2.1. Irreversible EGFR TKIs. Approximately 50% of
patients with acquired EGFR TKI resistance harbor a
secondary T790M mutation in EGFR. Second-generation
irreversible EGFR inhibitors, which bind irreversibly in
the ATP-binding pocket of EGFR through a covalent bond
at C797, were shown to be more potent inhibitors of the
second-site T790M mutation than erlotinib or gefitinib in
pre-clinical models [72, 80] (Figure 1). These inhibitors
are currently under clinical trials in patients with acquired
resistance. One of these agents, BIBW2992 (afatinib),
is able to target both EGFR and ERBB2 and overcome
T790M-driven acquired resistance . However, in clinical
studies, BIBW2992 did not prolong survival compared to
placebo in NSCLC patients who have developed acquired
resistance to gefitinib or erlotinib . Another agent in
this class of next generation EGFR TKIs, PF-002999804,
inhibits all ERBB family members and has been shown
to be effective against tumors harboring T790M [83, 84].
Unfortunately, resistance of EGFR T790M positive tumors
to PF00299804 was developed rapidly through amplification
of the EGFR T790M containing allele. This observation
has hampered further clinical development of this agent.
Chemical-genomic profiling studies indicate that the clinical
utility of these irreversible EGFR TKIs is likely to be limited
by the increased potency of these agents against both WT
and mutant EGFR and, thus, the narrow therapeutic window
of these irreversible inhibitors in the clinic .
6Chemotherapy Research and Practice
4.2.2. T790M Specific Inhibitors. Recently WZ4002, a new
inhibitor specifically targeting T790M gatekeeper mutation
in vitro and in vivo against T790M than against wild-
type EGFR  (Figure 1). These findings indicate that
the specificity of this class of inhibitors against the EGFR
T790M oncoprotein may provide the ability to achieve
clinical concentrations sufficient to effectively target tumor
cells that express EGFR T790M and spare cells that express
WT EGFR. Several agents in this promising class of EGFR
TKIs are currently under clinical development.
compensatory pathways that lead to acquired EGFR TKI
resistance may overcome resistance. For example, adding
a MET inhibitor may be beneficial to EGFR mutant lung
cancer patients whose tumors harbor MET amplification as
a mechanism of EGFR TKI resistance. Antibodies targeting
the MET ligand HGF (AMG102), MET itself (MetMAb),
and small molecule inhibitors against MET are currently
in clinical development (Figure 1). Moreover, due to the
importance of AXL signaling in acquired resistance to EGFR
TKI, the combination of small molecule kinase inhibitors
targeting AXL (XL880 or MP-470) or an AXL neutralizing
antibody with an EGFR TKI is also a potential approach to
of the PI3K/AKT and also MAPK signaling pathways. These
observations provide rational to combine EGFR inhibitors
with inhibitors of these pathways. For example, combination
therapy with an irreversible EGFR inhibitor and an inhibitor
of mTOR (rapamycin) lead to significant regression of
EGFR T790M/L858R mutant oncoprotein . Moreover,
dual inhibition of EGFR with an irreversible EGFR inhibitor
(afatinib) and the EGFR neutralizing antibody cetuximab
has recently shown promising activity in EGFR mutant lung
cancers with acquired EGFR TKI resistance that harbor an
EGFR T790M mutation .
Recently, a clinical trial was conducted to investigate
whether there would be any additional clinical benefit with
the addition of systemic chemotherapy to an EGFR TKI
in lung cancer patients. In the subgroup of 66 patients
with an EGFR mutation who received either single-agent
erlotinib or concurrent combination of chemotherapy and
respectively, in this trial. The data indicate that the addition
of chemotherapy to erlotinib did not appear to improve
treatment outcomes in patients with EGFR mutation .
4.2.4. Alternative EGFR TKI Dosing and Continuation Ther-
apy. A recent study incorporating mathematical modeling
significantly prolong the time to relapse without compro-
mising efficacy . Furthermore, continuation therapy that
incorporates cycling EGFR TKI treatment may suppress the
outgrowth of aggressive drug resistant clones that can be
discontinuation of EGFR TKI therapy . Based in part on
these data, there is biological rationale for the continuation
of EGFR TKI treatment upon tumor progression in patients.
ules and rational combination therapies are under active
investigation to determine if different dosing regiments can
significantly prolong the duration of response to EGFR TKI
treatment in patients.
The ultimate goal of investigations that aim to understand
the mechanisms of de novo and acquired EGFR TKI
resistance is to allow us to design rational strategies to
overcome resistance or to prevent resistance from developing
altogether in patients. The characterization of the biological
basis of EGFR TKI resistance will hopefully pave the way for
novel therapeutic strategies to optimize responses to EGFR
inhibition in EGFR mutant lung cancer patients by delaying
or preventing the emergence of dominant drug resistant
subclones that exist or are induced in an EGFR mutant
lung cancer. Systematic and comprehensive interrogation of
the genetic, epigenetic, and genomic alterations that drive
the development of resistance to EGFR TKI treatment are
underway and should yield rapid and substantial advances
that lead to improved therapeutic strategies and survival
outcomes for lung cancer patients.
 C. DeSantis, R. Siegel, and P. Bandi, “Breast cancer statistics
 R. Siegel, E. Ward, O. Brawley, and A. Jemal, “Cancer statistics,
2011: the impact of eliminating socioeconomic and racial
disparitiesonprematurecancer deaths,” CACancerJournalfor
Clinicians, vol. 61, no. 4, pp. 212–236, 2011.
 P. Goldstraw, J. Crowley, K. Chansky et al., “The IASLC lung
cancer staging project: proposals for the revision of the TNM
stage groupings in the forthcoming (seventh) edition of the
TNM classification of malignant tumours,” Journal of Thoracic
Oncology, vol. 2, no. 8, pp. 706–714, 2007.
 R. Sordella, D. W. Bell, D. A. Haber, and J. Settleman,
“Gefitinib-sensitizing EGFR mutations in lung cancer activate
anti-apoptotic pathways,” Science, vol. 305, no. 5687, pp.
 S. Tracy, T. Mukohara, M. Hansen, M. Meyerson, B. E.
Johnson, and P. A. J¨ anne, “Gefitinib induces apoptosis in
the EGFRL858R non-small-cell lung cancer cell line H3255,”
Cancer Research, vol. 64, no. 20, pp. 7241–7244, 2004.
 T. Mukohara, J. A. Engelman, N. H. Hanna et al., “Differential
effects of gefitinib and cetuximab on non-small-cell lung
cancers bearing epidermal growth factor receptor mutations,”
Journal of the National Cancer Institute, vol. 97, no. 16, pp.
 J. Amann, S. Kalyankrishna, P. P. Massion et al., “Aberrant
epidermal growth factor receptor signaling and enhanced
vol. 65, no. 1, pp. 226–235, 2005.
Chemotherapy Research and Practice7
 W. Pao, T. Y. Wang, G. J. Riely et al., “KRAS mutations and
primary resistance of lung adenocarcinomas to gefitinib or
erlotinib,” PLoS Medicine, vol. 2, no. 1, article e17, 2005.
 C. A. Pratilas, A. J. Hanrahan, E. Halilovic et al., “Genetic
predictors of MEK dependence in non-small cell lung cancer,”
Cancer Research, vol. 68, no. 22, pp. 9375–9383, 2008.
 S. V. Sharma, D. W. Bell, J. Settleman, and D. A. Haber,
“Epidermal growth factor receptor mutations in lung cancer,”
Nature Reviews Cancer, vol. 7, no. 3, pp. 169–181, 2007.
 T. S. Mok, Y. L. Wu, S. Thongprasert et al., “Gefitinib or
carboplatin-paclitaxel in pulmonary adenocarcinoma,” New
England Journal of Medicine, vol. 361, no. 10, pp. 947–957,
 T. Mitsudomi, S. Morita, Y. Yatabe et al., “Gefitinib versus
cisplatin plus docetaxel in patients with non-small-cell lung
cancer harbouring mutations of the epidermal growth factor
receptor (WJTOG3405): an open label, randomised phase 3
trial,” The Lancet Oncology, vol. 11, no. 2, pp. 121–128, 2010.
 T. J. Lynch, D. W. Bell, R. Sordella et al., “Activating
mutations in the epidermal growth factor receptor underlying
England Journal of Medicine, vol. 350, no. 21, pp. 2129–2139,
growth factor receptor mutations in lung cancer,” New
England Journal of Medicine, vol. 361, no. 10, pp. 958–967,
 D. B. Costa, S. Kobayashi, D. G. Tenen, and M. S. Huber-
man, “Pooled analysis of the prospective trials of gefitinib
monotherapy for EGFR-mutant non-small cell lung cancers,”
Lung Cancer, vol. 58, no. 1, pp. 95–103, 2007.
 V. A. Miller, G. J. Riely, M. F. Zakowski et al., “Molecular
characteristics of bronchioloalveolar carcinoma and adeno-
carcinoma, bronchioloalveolar carcinoma subtype, predict
response to erlotinib,” Journal of Clinical Oncology, vol. 26, no.
9, pp. 1472–1478, 2008.
 D. M. Jackman, V. A. Miller, L. A. Cioffredi et al., “Impact
of epidermal growth factor receptor and KRAS mutations on
clinical outcomes in previously untreated non-small cell lung
cancer patients: results of an online tumor registry of clinical
 H. Greulich, T. H. Chen, W. Feng et al., “Oncogenic transfor-
mation by inhibitor-sensitive and -resistant EGFR mutants,”
PLoS Medicine, vol. 2, no. 11, article e313, pp. 1167–1176,
 J. Y. Wu, S. G. Wu, C. H. Yang et al., “Lung cancer
with epidermal growth factor receptor exon 20 mutations is
associated with poor gefitinib treatment response,” Clinical
Cancer Research, vol. 14, no. 15, pp. 4877–4882, 2008.
 S. Maheswaran, L. V. Sequist, S. Nagrath et al., “Detection
of mutations in EGFR in circulating lung-cancer cells,” New
 M. Inukai, S. Toyooka, S. Ito et al., “Presence of epidermal
in non-small cell lung cancer,” Cancer Research, vol. 66, no. 16,
pp. 7854–7858, 2006.
presentations of the EGFR T790M mutation in lung cancer,”
Journal of Thoracic Oncology, vol. 4, no. 1, pp. 139–141, 2009.
 D. W. Bell, I. Gore, R. A. Okimoto et al., “Inherited suscepti-
bility to lung cancer may be associated with the T790M drug
resistance mutation in EGFR,” Nature Genetics, vol. 37, no. 12,
pp. 1315–1316, 2005.
 N. Girard, E. Lou, C. G. Azzoli et al., “Analysis of genetic
variants in never-smokers with lung cancer facilitated by
an internet-based blood collection protocol: a preliminary
report,” Clinical Cancer Research, vol. 16, no. 2, pp. 755–763,
 H. Vikis, M. Sato, M. James et al., “EGFR-T790M is a rare
lungcancer susceptibilityallele withenhanced kinaseactivity,”
Cancer Research, vol. 67, no. 10, pp. 4665–4670, 2007.
 R. Rosell, M. A. Molina, C. Costa et al., “Pretreatment EGFR
T790M mutation and BRCA1 mRNA expression in erlotinib-
treated advanced non-small-cell lung cancer patients with
EGFR mutations,” Clinical Cancer Research, vol. 17, no. 5, pp.
 M. N. Balak, Y. Gong, G. J. Riely et al., “Novel D761Y and
common secondary T790M mutations in epidermal growth
factor receptor-mutant lung adenocarcinomas with acquired
resistance to kinase inhibitors,” Clinical Cancer Research, vol.
12, no. 21, pp. 6494–6501, 2006.
 M. L. Sos, M. Koker, B. A. Weir et al., “PTEN loss contributes
to erlotinib resistance in EGFR-mutant lung cancer by acti-
vation of akt and EGFR,” Cancer Research, vol. 69, no. 8, pp.
 I. Vivanco, D. Rohle, M. Versele et al., “The phosphatase and
tensin homolog regulates epidermal growth factor receptor
(EGFR) inhibitor response by targeting EGFR for degrada-
tion,” Proceedings of the National Academy of Sciences of the
in Japanese lung cancer patients,” Lung Cancer, vol. 54, no. 2,
pp. 209–215, 2006.
tion obscures detection of a biologically significant resistance
mutation in EGFR-amplified lung cancer,” Journal of Clinical
Investigation, vol. 116, no. 10, pp. 2695–2706, 2006.
 Y. Gong, E. Yao, R. Shen et al., “High expression levels of total
IGF-1R and sensitivity of NSCLC cells in vitro to an anti-lGF-
1R antibody (R1507),” PLoS ONE, vol. 4, no. 10, Article ID
 S. V. Sharma, D. Y. Lee, B. Li et al., “A chromatin-mediated
reversible drug-tolerant state in cancer cell subpopulations,”
Cell, vol. 141, no. 1, pp. 69–80, 2010.
 Y. Ben-Neriah and M. Karin, “Inflammation meets cancer,
with NF-κB as the matchmaker,” Nature Immunology, vol. 12,
no. 8, pp. 715–723, 2011.
 T. G. Bivona, H. Hieronymus, J. Parker et al., “FAS and NF-
κBsignalling modulatedependence oflung cancers onmutant
EGFR,” Nature, vol. 471, no. 7339, pp. 523–526, 2011.
 P. Workman and P. A. Clarke, “Resisting targeted therapy: fifty
ways to leave your EGFR,” Cancer Cell, vol. 19, no. 4, pp. 437–
 D. Jackman, W. Pao, G. J. Riely et al., “Clinical definition
of acquired resistance to epidermal growth factor receptor
tyrosine kinase inhibitors in non-small-cell lung cancer,”
Journal of Clinical Oncology, vol. 28, no. 2, pp. 357–360, 2010.
 S. Kobayashi, T. J. Boggon, T. Dayaram et al., “EGFR mutation
and resistance of non-small-cell lung cancer to gefitinib,” New
 W. Pao, V. A. Miller, K. A. Politi et al., “Acquired resistance
of lung adenocarcinomas to gefitinib or erlotinib is associated
with a second mutation in the EGFR kinase domain,” PLoS
Medicine, vol. 2, no. 3, article e73, 2005.
8 Chemotherapy Research and Practice
 N. P. Shah, J. M. Nicoll, B. Nagar et al., “Multiple BCR-ABL
kinase domain mutations confer polyclonal resistance to the
tyrosine kinase inhibitor imatinib (STI571) in chronic phase
and blast crisis chronic myeloid leukemia,” Cancer Cell, vol. 2,
no. 2, pp. 117–125, 2002.
 C. H. Yun, K. E. Mengwasser, A. V. Toms et al., “The T790M
mutation in EGFR kinase causes drug resistance by increasing
the affinity for ATP,” Proceedings of the National Academy of
Sciences of the United States of America, vol. 105, no. 6, pp.
activity of epidermal growth factor receptor kinase mutant
alleles is enhanced by the T790M drug resistance mutation,”
Cancer Research, vol. 67, no. 15, pp. 7319–7326, 2007.
 R. Mulloy, A. Ferrand, Y. Kim et al., “Epidermal growth factor
receptor mutants from human lung cancers exhibit enhanced
catalytic activity and increased sensitivity to gefitinib,” Cancer
Research, vol. 67, no. 5, pp. 2325–2330, 2007.
 G. J. Riely, M. G. Kris, B. Zhao et al., “Prospective assessment
of discontinuation and reinitiation of erlotinib or gefitinib
in patients with acquired resistance to erlotinib or gefitinib
followed by the addition of everolimus,” Clinical Cancer
Research, vol. 13, no. 17, pp. 5150–5155, 2007.
 D. T. Milton, G. J. Riely, W. Pao, V. A. Miller, M. G. Kris, and
R. T. Heelan, “Molecular on/off switch,” Journal of Clinical
Oncology, vol. 24, no. 30, pp. 4940–4942, 2006.
 T. Kurata, K. Tamura, H. Kaneda et al., “Effect of re-treatment
Annals of Oncology, vol. 15, no. 1, p. 173, 2004.
 S. Yano, E. Nakataki, S. Ohtsuka et al., “Retreatment of lung
adenocarcinoma patients with gefitinib who had experienced
favorable results from their initial treatment with this selective
epidermal growth factor receptor inhibitor: a report of three
cases,” Oncology Research, vol. 15, no. 2, pp. 107–111, 2005.
 J. Bean, G. J. Riely, M. Balak et al., “Acquired resistance to
epidermal growth factor receptor kinase inhibitors associated
with a novel T854A mutation in a patient with EGFR-mutant
lung adenocarcinoma,” Clinical Cancer Research, vol. 14, no.
22, pp. 7519–7525, 2008.
 D. B. Costa, S. T. Schumer, D. G. Tenen, and S. Kobayashi,
“Differential responses to Erlotinib in Epidermal Growth
Factor Receptor (EGFR)-mutated lung cancers with acquired
resistance to gefitinib carrying the L747S or T790M secondary
mutations,” Journal of Clinical Oncology, vol. 26, no. 7, pp.
 E. Avizienyte, R. A. Ward, and A. P. Garner, “Comparison of
the EGFR resistance mutation profiles generated by EGFR-
targeted tyrosine kinase inhibitors and the impact of drug
combinations,” Biochemical Journal, vol. 415, no. 2, pp. 197–
 J. Bean, C. Brennan, J. Y. Shih et al., “MET amplification
occurs with or without T790M mutations in EGFR mutant
lung tumors with acquired resistance to gefitinib or erlotinib,”
Proceedings of the National Academy of Sciences of the United
States of America, vol. 104, no. 52, pp. 20932–20937, 2007.
 J. A. Engelman, K. Zejnullahu, T. Mitsudomi et al., “MET
amplification leads to gefitinib resistance in lung cancer by
activating ERBB3 signaling,” Science, vol. 316, no. 5827, pp.
 S. Yano, W. Wang, Q. Li et al., “Hepatocyte growth factor
induces gefitinib resistance of lung adenocarcinoma with epi-
dermal growth factor receptor-activating mutations,” Cancer
Research, vol. 68, no. 22, pp. 9479–9487, 2008.
 A. B. Turke, K. Zejnullahu, Y. L. Wu et al., “Preexistence
and clonal selection of MET amplification in EGFR mutant
NSCLC,” Cancer Cell, vol. 17, no. 1, pp. 77–88, 2010.
 L. V. Sequist, B. A. Waltman, D. Dias-Santagata et al., “Geno-
typic and histological evolution of lung cancers acquiring
resistance to EGFR inhibitors,” Science Translational Medicine,
vol. 3, no. 75, Article ID 75ra26, 2011.
transition is a determinant of sensitivity of non-small-cell
lung carcinoma cell lines and xenografts to epidermal growth
 B. C. Fuchs, T. Fujii, J. D. Dorfman et al., “Epithelial-to-
mesenchymal transition and integrin-linked kinase mediate
sensitivity to epidermal growth factor receptor inhibition in
human hepatoma cells,” Cancer Research, vol. 68, no. 7, pp.
 R. L. Yauch, T. Januario, D. A. Eberhard et al., “Epithelial
versus mesenchymal phenotype determines in vitro sensitivity
and predicts clinical activity of erlotinib in lung cancer
patients,” Clinical Cancer Research, vol. 11, no. 24, pp. 8686–
 C. D. Coldren, B. A. Helfrich, S. E. Witta et al., “Baseline gene
expression predicts sensitivity to gefitinib in non-small cell
lung cancer cell lines,” Molecular Cancer Research, vol. 4, no.
8, pp. 521–528, 2006.
 K. Suda, K. Tomizawa, M. Fujii et al., “Epithelial to mesenchy-
mal transition in an epidermal growth factor receptor-mutant
lung cancer cell line with acquired resistance to erlotinib,”
Journal of Thoracic Oncology, vol. 6, no. 7, pp. 1152–1161,
 J. H. Chung, J. K. Rho, X. Xu et al., “Clinical and molecular
evidences of epithelial to mesenchymal transition in acquired
in small-cell lung cancers in patients who have never smoked,”
New England Journal of Medicine, vol. 355, no. 2, pp. 213–215,
 R. Morinaga, I. Okamoto, K. Furuta et al., “Sequential
occurrence of non-small cell and small cell lung cancer with
the same EGFR mutation,” Lung Cancer, vol. 58, no. 3, pp.
 A. Tatematsu, J. Shimizu, Y. Murakami et al., “Epidermal
growth factor receptor mutations in small cell lung cancer,”
Clinical Cancer Research, vol. 14, no. 19, pp. 6092–6096, 2008.
 Z. Zhang, J. C. Lee, L. Lin et al., “Activation of the AXL kinase
causes resistance to EGFR-targeted therapy in lung cancer,”
Nature Genetics, vol. 44, no. 8, pp. 852–860, 2012.
 M. Guix, A. C. Faber, S. E. Wang et al., “Acquired resistance to
EGFR tyrosine kinase inhibitors in cancer cells is mediated by
loss of IGF-binding proteins,” Journal of Clinical Investigation,
vol. 118, no. 7, pp. 2609–2619, 2008.
 Y. Kokubo, A. Gemma, R. Noro et al., “Reduction of PTEN
protein and loss of epidermal growth factor receptor gene
mutation in lung cancer with natural resistance to gefitinib
(IRESSA),” British Journal of Cancer, vol. 92, no. 9, pp. 1711–
 F. Yamasaki, M. J. Johansen, D. Zhang et al., “Acquired resis-
tance to erlotinib in A-431 epidermoid cancer cells requires
down-regulation of MMAC1/PTEN and up-regulation of
phosphorylated Akt,” Cancer Research, vol. 67, no. 12, pp.
Chemotherapy Research and Practice9 Download full-text
 K. Yonesaka, K. Zejnullahu, I. Okamoto et al., “Activation of
ERBB2 signaling causes resistance to the EGFR-directed ther-
apeutic antibody cetuximab,” Science Translational Medicine,
vol. 3, no. 99, article 99ra86, 2011.
 K. Politi, P. D. Fan, R. Shen, M. Zakowski, and H. Varmus,
“Erlotinib resistance in mouse models of epidermal growth
factor receptor-induced lung adenocarcinoma.,” Disease Mod-
els & Mechanisms, vol. 3, no. 1-2, pp. 111–119, 2010.
 P. A. Janne, J. H. Schellens, J. A. Engelman et al., “Preliminary
activity and safety results from a phase I clinical trial of PF-
00299804, an irreversible pan-HER inhibitor, in patients (pts)
with NSCLC,” Journal of Clinical Oncology, vol. 26, abstract
 T. A. Carter, L. M. Wodicka, N. P. Shah et al., “Inhibition
of drug-resistant mutants of ABL, KIT, and EGF receptor
kinases,” Proceedings of the National Academy of Sciences of the
United States of America, vol. 102, no. 31, pp. 11011–11016,
 D. F. Lee and M. C. Hung, “Advances in targeting IKK
and IKK-related kinases for cancer therapy,” Clinical Cancer
Research, vol. 14, no. 18, pp. 5656–5662, 2008.
NEDD8-activating enzyme inhibitor, is active in diffuse large
B-cell lymphoma models: rationale for treatment of NF-κB-
dependent lymphoma,” Blood, vol. 116, no. 9, pp. 1515–1523,
 M. Karin, Y. Yamamoto, and Q. M. Wang, “The IKK NF-
κB system: a treasure trove for drug development,” Nature
Reviews Drug Discovery, vol. 3, no. 1, pp. 17–26, 2004.
 Y. Gong, R. Somwar, K. Politi et al., “Induction of BIM is
essential for apoptosis triggered by EGFR kinase inhibitors
in mutant EGFR-dependent lung adenocarcinomas,” PLoS
Medicine, vol. 4, no. 10, article e294, pp. 1655–1668, 2007.
 D. B. Costa, B. Halmos, A. Kumar et al., “BIM mediates EGFR
tyrosine kinase inhibitor-induced apoptosis in lung cancers
with oncogenic EGFR mutations,” PLoS Medicine, vol. 4, no.
10, pp. 1669–1680, 2007.
 A. Faber, R. B. Corcoran, H. Ebi et al., “BIM expression
in treatment naive cancers predicts responsiveness to kinase
inhibitors,” Cancer Discovery, vol. 1, no. 4, pp. 352–365, 2011.
 K. P. Ng, A. M. Hillmer, C. T. H. Chuah et al., “A common
BIM deletion polymorphism mediates intrinsic resistance and
inferior responses to tyrosine kinase inhibitors in cancer,”
Nature Medicine, vol. 18, no. 4, pp. 521–528, 2012.
of the EGF receptor may circumvent acquired resistance to
gefitinib,” Proceedings of the National Academy of Sciences of
the United States of America, vol. 102, no. 21, pp. 7665–7670,
 D. Li, L. Ambrogio, T. Shimamura et al., “BIBW2992, an irre-
versible EGFR/HER2 inhibitor highly effective in preclinical
lung cancer models,” Oncogene, vol. 27, no. 34, pp. 4702–4711,
 V. A. Miller, V. Hirsh, J. Cadranel et al., “Afatinib versus
placebo for patients with advanced, metastatic non-small-cell
lung cancer after failure of erlotinib, gefitinib, or both, and
one or two lines of chemotherapy (LUX-Lung 1): a phase 2b/3
 J. A. Engelman, K. Zejnullahu, C. M. Gale et al., “PF00299804,
an irreversible pan-ERBB inhibitor, is effective in lung cancer
models with EGFR and ERBB2 mutations that are resistant to
gefitinib,” Cancer Research, vol. 67, no. 24, pp. 11924–11932,
 A. J. Gonzales, K. E. Hook, I. W. Althaus et al., “Antitumor
activity and pharmacokinetic properties of PF-00299804,
a second-generation irreversible pan-erbB receptor tyrosine
kinase inhibitor,” Molecular Cancer Therapeutics, vol. 7, no. 7,
pp. 1880–1889, 2008.
 M. L. Sos, H. B. Rode, S. Heynck et al., “Chemogenomic pro-
filing provides insights into the limited activity of irreversible
EGFR inhibitors in tumor cells expressing the T790M EGFR
resistance mutation,” Cancer Research, vol. 70, no. 3, pp. 868–
 W. Zhou, D. Ercan, L. Chen et al., “Novel mutant-selective
EGFR kinase inhibitors against EGFR T790M,” Nature, vol.
462, no. 7276, pp. 1070–1074, 2009.
 D. Li, T. Shimamura, H. Ji et al., “Bronchial and peripheral
murine lung carcinomas induced by T790M-L858R mutant
EGFR respond to HKI-272 and rapamycin combination
therapy,” Cancer Cell, vol. 12, no. 1, pp. 81–93, 2007.
 Y. Y. Janjigian, H. J. Groen, L. Horn et al., “Activity and
tolerability of afatinib (BIBW 2992) and cetuximab in NSCLC
patients with acquired resistance to erlotinib or gefitinib,”
Journal Of Clinical Oncology, vol. 29, supplement, abstract
 P.A.J¨ anne,X.Wang,M.A.Socinskietal.,“Randomizedphase
II trial of erlotinib alone or with carboplatin and paclitaxel
in patients who were never or light former smokers with
advanced lung adenocarcinoma: CALGB 30406 trial,” Journal
of Clinical Oncology, vol. 30, no. 17, pp. 2063–2069, 2012.
 J. Chmielecki, J. Foo, G. R. Oxnard et al., “Optimization of
dosing for EGFR-mutant non-small cell lung cancer with evo-
lutionary cancer modeling,” Science Translational Medicine,
vol. 3, no. 90, Article ID 90ra59, 2011.