HER2 kinase domain mutation results in constitutive phosphorylation and activation of HER2 and EGFR and resistance to EGFR tyrosine kinase inhibitors

Gefitinib: re-emerging from the shadows

SUMMARY In the past decade, the identification of mutations in the EGFR gene and the sensitivity of activating mutations to EGF receptor–tyrosine kinase inhibitors has improved survival in a subset of non-small-cell lung cancer patients. Over 70% of patients with EGFR mutations have a response to gefitinib therapy. Gefitinib, a first-generation EGF receptor–tyrosine kinase inhibitor, is well tolerated and continues to be widely used. However, eventually most patients develop resistance to gefitinib. This article reviews the pharmacology of gefitinib and summarizes the clinical trials that have resulted in its current day indications.

Targeted therapy for NSCLC with driver mutations

INTRODUCTION

Activating mutations of the epidermal growth factor receptor (EGFR) gene and rearrangement of anaplastic lymphoma kinase (ALK) gene best illustrate the therapeutic relevance of molecular characterization in non-small cell lung cancer (NSCLC) patients. Several genetic aberrations with a potential prognostic or predictive role have been identified, mainly in adenocarcinoma subtype, including ROS1, RET, MET, HER2, BRAF and KRAS. More recently oncogenic drivers, such as DDR2, FGFR1 and PI3KCA, have been characterized in squamous cell lung carcinoma (SCC) and target agents are currently under evaluation. The aim of this review is to summarize the growing scenario of new targetable oncogenes in NSCLC.

AREAS COVERED

For this review article all published data on NSCLC genomic alterations, including the techniques employed for oncogenic drivers identification, the prevalence of each one in lung cancer subtypes, the preclinical data corroborating their role in tumorigenesis and the potential biological tailored agents tested and under evaluation were collected and analyzed using PubMed.

EXPERT OPINION

Oncogenic products represent reliable targets for drug therapy and the expanding knowledge of molecular pathways involved in lung tumorigenesis is resulting in a dramatic change of treatment strategies leading to an improvement in disease and symptom control, extending life duration and improving quality of life.

Lung cancer in never smokers: disease characteristics and risk factors

It is estimated that approximately 25% of all lung cancer cases are observed in never-smokers and its incidence is expected to increase due to smoking prevention programs. Risk factors for the development of lung cancer described include second-hand smoking, radon exposure, occupational exposure to carcinogens and to cooking oil fumes and indoor coal burning. Other factors reported are infections (HPV and Mycobacterium tuberculosis), hormonal and diatery factors and diabetes mellitus. Having an affected relative also increases the risk for lung cancer while recent studies have identified several single nucleotide polymorphisms associated with increased risk for lung cancer development in never smokers. Distinct clinical, pathology and molecular characteristics are observed in lung cancer in never smokers; more frequently is observed in females and adenocarcinoma is the predominant histology while it has a different pattern of molecular alterations. The purpose of this review is to summarize our current knowledge of this disease.

Angiogenesis-related pathways in the pathogenesis of ovarian cancer

Ovarian Cancer represents the most fatal type of gynecological malignancies. A number of processes are involved in the pathogenesis of ovarian cancer, especially within the tumor microenvironment. Angiogenesis represents a hallmark phenomenon in cancer, and it is responsible for tumor spread and metastasis in ovarian cancer, among other tumor types, as it leads to new blood vessel formation. In recent years angiogenesis has been given considerable attention in order to identify targets for developing effective anti-tumor therapies. Growth factors have been identified to play key roles in driving angiogenesis and, thus, the formation of new blood vessels that assist in "feeding" cancer. Such molecules include the vascular endothelial growth factor (VEGF), the platelet derived growth factor (PDGF), the fibroblast growth factor (FGF), and the angiopoietin/Tie2 receptor complex. These proteins are key players in complex molecular pathways within the tumor cell and they have been in the spotlight of the development of anti-angiogenic molecules that may act as stand-alone therapeutics, or in concert with standard treatment regimes such as chemotherapy. The pathways involved in angiogenesis and molecules that have been developed in order to combat angiogenesis are described in this paper.

Sensitive methods for the detection of an insertion in exon 20 of the HER2 gene in the metastasis of non-small cell lung cancer to the central nervous system

The HER2 (ErbB2/neu) protein is a member of the HER (ErbB) receptor family (EGFR, HER2, HER3 and HER4) that expresses tyrosine kinase activity in the intracellular domain. EGFR and HER2 overexpression is observed in numerous types of cancer, nevertheless, the susceptibility of patients with non-small cell lung cancer (NSCLC) to therapy with EGFR and HER2 tyrosine kinase inhibitors (TKIs) depends on mutations present in the respective coding genes (driver mutations). In the present study, PCR and amplified DNA fragment length analysis (FLA) were used along with the multi-temperature single-strand conformation polymorphism (MSSCP) technique in order to identify the 12 base pair insertion in exon 20 of the HER2 gene in 143 patients with NSCLC metastasis to the central nervous system. The prevalence of the HER2 gene mutation was correlated with mutations in the EGFR and BRAF genes. The insertion in exon 20 of the HER2 gene was observed in a single 77-year-old, non-smoking male, with poorly-differentiated adenocarcinoma of the lung (1.5% of adenocarcinoma patients). No other genetic abnormalities were identified in this patient. In the therapy of NSCLC patients with HER2 gene mutations, drugs that inhibit the EGFR and HER2 receptors, for example afatinib, may be effective. The identification of other driving mutations in NSCLC cells appears to be key to the appropriate qualification of molecular targeted therapies.

Analysis of conformational determinants underlying HSP90-kinase interaction

The role of HSP90 in stabilization of oncogenic tyrosine kinases made it an attractive therapeutic target for treating cancer but the molecular basis underlying the interaction between the HSP90 chaperone and client kinases is not elucidated yet. Using kinase inhibitors we show that the inactive conformation of ERBB2 does not interact with HSP90 chaperone and is thus not amenable to degradation upon HSP90 inhibitor treatment, while active ERBB2 kinase conformation promotes interaction with the HSP90 machinery and thus is degraded upon HSP90 inhibitor treatment. Interestingly, the kinase-chaperone interaction is disrupted in case of BCR-ABL and FLT3-ITD when bound to inhibitors irrespective of whether they block the kinase in an active or inactive conformation and thus our results indicate that the stability of the active kinase conformation varies between different kinases.

Whole exome sequence analysis of serous borderline tumors of the ovary

OBJECTIVE

Serous borderline tumor (SBT) is a unique histopathologic entity of the ovary, believed to be intermediate between benign cystadenoma and invasive low-grade serous carcinoma. While somatic mutations in the KRAS or BRAF, and rarely ERBB2, genes have been well characterized in SBTs, other genetic alterations have not been described. Toward a more comprehensive understanding of the molecular genetic architecture of SBTs, we undertook whole exome sequencing of this tumor type.

METHODS

Following pathologic review and laser capture microdissection to enrich for tumor cells, whole exomes were prepared from DNA of two independent SBTs and subjected to massively parallel DNA sequencing.

RESULTS

Both tumors contained an activating mutation of the BRAF gene. A total of 15 additional somatic mutations were identified, nine in one tumor and six in the other. Eleven were missense mutations and four were nonsense or deletion mutations. Fourteen of the 16 genes found to be mutated in this study have been reported to be mutated in other cancers. Furthermore, 12 of these genes are mutated in ovarian cancers. The FBXW7 and KIAA1462 genes are noteworthy candidates for a pathogenic role in serous borderline tumorigenesis.

CONCLUSIONS

These findings suggest that a very small number of somatic genetic mutations are characteristic of SBTs of the ovary, thus supporting their classification as a relatively genetically stable tumor type. The mutant genes described herein represent novel candidates for the pathogenesis of ovarian SBT.

A neu view of invasive lobular breast cancer

Genome sequencing of relapsed, invasive lobular breast cancer identified actionable mutations in 86% of the cases. HER2 alterations occur in 27% of the cases, including 4 cases with activating HER2 mutations and 1 with a novel HER2-GRB7 gene fusion. This fusion links the HER2 tyrosine kinase domain to the GRB7 src homology 2 (SH2) domain.

Oncogenic ERBB3 mutations in human cancers

The human epidermal growth factor receptor (HER) family of tyrosine kinases is deregulated in multiple cancers either through amplification, overexpression, or mutation. ERBB3/HER3, the only member with an impaired kinase domain, although amplified or overexpressed in some cancers, has not been reported to carry oncogenic mutations. Here, we report the identification of ERBB3 somatic mutations in ~11% of colon and gastric cancers. We found that the ERBB3 mutants transformed colonic and breast epithelial cells in a ligand-independent manner. However, the mutant ERBB3 oncogenic activity was dependent on kinase-active ERBB2. Furthermore, we found that anti-ERBB antibodies and small molecule inhibitors effectively blocked mutant ERBB3-mediated oncogenic signaling and disease progression in vivo.

Going beyond EGFR

a substantial proportion of non-small-cell lung cancer (NSCLC), and adenocarcinoma in particular, depends on a so-called 'driver mutation' for their malignant phenotype. This genetic alteration induces and sustains tumorigenesis, and targeting of its protein product can result in growth inhibition, tumor response and increased patient survival. NSCLC can thus be subdivided into clinically relevant molecular subsets. Mutations in EGFR best illustrate the therapeutic relevance of molecular classification. This article reviews the scope of presently known driving molecular alterations, including ROS1, BRAF, KRAS, HER2 and PIK3CA, with a special emphasis on aLK rearrangements, and outlines their potential therapeutic applications.

Activating Mutations in ERBB2 and Their Impact on Diagnostics and Treatment

Despite the ongoing “war on cancer,” cancer remains one of the major causes of human morbidity and mortality. A new paradigm of targeted therapies holds the most promise for the future, making identification of tumor-specific therapeutic targets of prime importance. ERBB2/HER2, best known for its role in breast cancer tumorigenesis, can be targeted by two types of pharmacological manipulation: antibody therapy against the extracellular receptor domain and small molecule compounds against the intracellular tyrosine kinase domain. Aberrant activation of ERBB2 by gene amplification has been shown to participate in the pathophysiology of breast, ovarian, gastric, colorectal, lung, brain, and head and neck tumors. However, the advent of next-generation sequencing technologies has enabled efficient identification of activating molecular alterations of ERBB2. In this review, we will focus on the functional role of these somatic mutations that cause ERBB2 receptor activation. We will additionally discuss the current preclinical and clinical therapeutic strategies for targeting mutationally activated ERBB2.

Acquired substrate preference for GAB1 protein bestows transforming activity to ERBB2 kinase lung cancer mutants

Activating mutations in the αC-β4 loop of the ERBB2 kinase domain, such as ERBB2(YVMA) and ERBB2(G776VC), have been identified in human lung cancers and found to drive tumor formation. Here we observe that the docking protein GAB1 is hyper-phosphorylated in carcinomas from transgenic mice and in cell lines expressing these ERBB2 cancer mutants. Using dominant negative GAB1 mutants lacking canonical tyrosine residues for SHP2 and PI3K interactions or lentiviral shRNA that targets GAB1, we demonstrate that GAB1 phosphorylation is required for ERBB2 mutant-induced cell signaling, cell transformation, and tumorigenesis. An enzyme kinetic analysis comparing ERBB2(YVMA) to wild type using physiologically relevant peptide substrates reveals that ERBB2(YVMA) kinase adopts a striking preference for GAB1 phosphorylation sites as evidenced by ∼150-fold increases in the specificity constants (kcat/Km) for several GAB1 peptides, and this change in substrate selectivity was predominantly attributed to the peptide binding affinities as reflected by the apparent Km values. Furthermore, we demonstrate that ERBB2(YVMA) phosphorylates GAB1 protein ∼70-fold faster than wild type ERBB2 in vitro. Notably, the mutation does not significantly alter the Km for ATP or sensitivity to lapatinib, suggesting that, unlike EGFR lung cancer mutants, the ATP binding cleft of the kinase is not significantly changed. Taken together, our results indicate that the acquired substrate preference for GAB1 is critical for the ERBB2 mutant-induced oncogenesis.

Relapsed classic E-cadherin (CDH1)-mutated invasive lobular breast cancer shows a high frequency of HER2 (ERBB2) gene mutations

PURPOSE

We queried whether comprehensive genomic profiling using a next-generation sequencing-based assay could identify novel and unanticipated targets of therapy for patients with relapsed invasive lobular carcinoma (ILC).

EXPERIMENTAL DESIGN

DNA sequencing (Illumina HiSeq 2000) was conducted for 3,320 exons of 182 cancer-related genes and 37 introns of 14 genes frequently rearranged in cancer on indexed, adaptor-ligated, hybridization-captured libraries using DNA isolated from formalin-fixed paraffin-embedded sections from 22 histologically verified ILC.

RESULTS

A total of 75 genomic alterations were identified with an average of 3.4 alterations per tumor (range, 1-6), of which 35 were actionable for an average of 1.59 actionable alterations per patient (range, 0-3). Nineteen of 22 (86%) of the ILC samples harbored at least one actionable alteration. Six (27%) cases featured alterations in ERRB2 including 4 (18%) with ERBB2 mutation, 1 (5%) with an ERBB2 gene fusion, and 1 (5%) with an ERBB2 copy number gain (amplification). The enrichment of ERBB2 mutations/fusion in CDH1-mutated ILC (5 of 22, 23%) compared with the 5 ERBB2 mutations in a series of 286 non-CDH1-mutated breast cancers from which the ILC cases were obtained (5 of 286, 2%) was significant (P = 0.0006).

CONCLUSIONS

Comprehensive genomic profiling of relapsed CDH1-mutated ILC revealed actionable genomic alterations in 86% of cases, featured a high incidence of ERBB2 alterations, and can reveal actionable alterations that can inform treatment decisions for patients with ILC.

[Advances on driver oncogenes of lung adenocarcinoma]

近来研究证实肺腺癌具有与致癌作用及靶向药物疗效有关的独特分子特征，这些分子改变被视为驱动基因，负责恶性病变的发生和维持。目前发现约50%肺腺癌携带驱动基因，其中EGFR通路起重要作用。本文将对肺腺癌驱动基因的意义及相关研究进行综述。

[The molecular biology of epithelial ovarian cancer]

Epithelial ovarian cancer frequently presents at an advanced stage where the cornerstone of management remains surgery and platinum-based chemotherapy. Unfortunately, despite sometimes dramatic initial responses, advanced ovarian cancer almost invariably relapses. Little progress has been made in the identification of effective targeted-therapies for ovarian cancer. The majority of clinical trials investigating novel agents have been negative and the only approved targeted-therapy is bevacizumab, for which reliable predictive biomarkers still elude us. Ovarian cancer is treated as a uniform disease. Yet, biological studies have highlighted the heterogeneity of this malignancy with marked differences in histology, oncogenesis, prognosis, chemo-responsiveness, and molecular profile. Recent high throughput molecular analyses have identified a huge number of genomic/phenotypic alterations. Broadly speaking, high grade serous carcinomas (type II) display significant genomic instability and numerous amplifications and losses; low grade (type I) tumors are genomically stable but display frequent mutations. Importantly, many of these genomic alterations relate to known oncogenes for which targeted-therapies are available or in development. There is today a real potential for personalized medicine in ovarian cancer. We will review the current literature regarding the molecular characterization of epithelial ovarian cancer and discuss the biological rationale for a number of targeted strategies. In order to translate these biological advances into meaningful clinical improvements for our patients, it is imperative to incorporate translational research in ovarian cancer trials, a number of strategies will be proposed such as the acquisition of quality tumor samples, including sequential pre- and post-treatment biopsies, the potential of liquid biopsies, and novel trial designs more adapted to the molecular era of ovarian cancer research.

Activating HER2 mutations in HER2 gene amplification negative breast cancer

Data from 8 breast cancer genome-sequencing projects identified 25 patients with HER2 somatic mutations in cancers lacking HER2 gene amplification. To determine the phenotype of these mutations, we functionally characterized 13 HER2 mutations using in vitro kinase assays, protein structure analysis, cell culture, and xenograft experiments. Seven of these mutations are activating mutations, including G309A, D769H, D769Y, V777L, P780ins, V842I, and R896C. HER2 in-frame deletion 755-759, which is homologous to EGF receptor (EGFR) exon 19 in-frame deletions, had a neomorphic phenotype with increased phosphorylation of EGFR or HER3. L755S produced lapatinib resistance, but was not an activating mutation in our experimental systems. All of these mutations were sensitive to the irreversible kinase inhibitor, neratinib. These findings show that HER2 somatic mutation is an alternative mechanism to activate HER2 in breast cancer and they validate HER2 somatic mutations as drug targets for breast cancer treatment.

SIGNIFICANCE

We show that the majority of HER2 somatic mutations in breast cancer patients are activating mutations that likely drive tumorigenesis. Several patients had mutations that are resistant to the reversible HER2 inhibitor lapatinib, but are sensitive to the irreversible HER2 inhibitor, neratinib. Our results suggest that patients with HER2 mutation–positive breast cancers could benefit from existing HER2-targeted drugs.

Mechanisms of acquired resistance to targeted cancer therapies

Drugs that target genomically defined vulnerabilities in human tumors have now been clinically validated as effective cancer therapies. However, the relatively rapid acquisition of resistance to such treatments that is observed in virtually all cases significantly limits their utility and remains a substantial challenge to the clinical management of advanced cancers. As molecular mechanisms of resistance have begun to be elucidated, new strategies to overcome or prevent the development of resistance have begun to emerge. In some cases, specific mutational mechanisms contribute directly to acquired drug resistance, and in other cases it appears that nonmutational and possibly epigenetic mechanisms play a significant role. This article discusses the various genetic and nongenetic mechanisms of acquired drug resistance that have been reported in the context of 'rationally targeted' drug therapies.

Trastuzumab-resistant cells rely on a HER2-PI3K-FoxO-survivin axis and are sensitive to PI3K inhibitors

The antibody trastuzumab is approved for treatment of patients with HER2 (ERBB2)-overexpressing breast cancer. A significant fraction of these tumors are either intrinsically resistant or acquire resistance rendering the drug ineffective. The development of resistance has been attributed to failure of the antibody to inhibit phosphoinositide 3-kinase (PI3K), which is activated by the HER2 network. Herein, we examined the effects of PI3K blockade in trastuzumab-resistant breast cancer cell lines. Treatment with the pan-PI3K inhibitor XL147 and trastuzumab reduced proliferation and pAKT levels, triggering apoptosis of trastuzumab-resistant cells. Compared with XL147 alone, the combination exhibited a superior antitumor effect against trastuzumab-resistant tumor xenografts. Furthermore, treatment with XL147 and trastuzumab reduced the cancer stem-cell (CSC) fraction within trastuzumab-resistant cells both in vitro and in vivo. These effects were associated with FoxO-mediated inhibition of transcription of the antiapoptosis gene survivin (BIRC5) and the CSC-associated cytokine interleukin-8. RNA interference-mediated or pharmacologic inhibition of survivin restored sensitivity to trastuzumab in resistant cells. In a cohort of patients with HER2-overexpressing breast cancer treated with trastuzumab, higher pretreatment tumor levels of survivin RNA correlated with poor response to therapy. Together, our results suggest that survivin blockade is required for therapeutic responses to trastuzumab and that by combining trastuzumab and PI3K inhibitors, CSCs can be reduced within HER2(+) tumors, potentially preventing acquired resistance to anti-HER2 therapy.

Advancing personalized cancer medicine in lung cancer

Although improvements in genomic technologies during the past decade have greatly advanced our understanding of the genomic alterations that contribute to lung cancer, and the disease has (to a degree) become a paradigm for individualized cancer treatment in solid tumors, additional challenges must be addressed before the goal of personalized cancer therapy can become a reality for lung cancer patients.

Apocrine-eccrine carcinomas: molecular and immunohistochemical analyses

Apocrine-eccrine carcinomas are rare and associated with poor prognosis. Currently there is no uniform treatment guideline. Chemotherapeutic drugs that selectively target cancer-promoting pathways may complement conventional therapeutic approaches. However, studies on genetic alterations and EGFR and Her2 status of apocrine-eccrine carcinomas are few in number. In addition, hormonal studies have not been comprehensive and performed only on certain subsets of apocrine-eccrine carcinomas. To investigate whether apocrine-eccrine carcinomas express hormonal receptors or possess activation of oncogenic pathways that can be targeted by available chemotherapeutic agent we performed immunohistochemistry for AR, PR, ER, EGFR, and HER2 expression; fluorescence in situ hybridization (FISH) for EGFR and ERBB2 gene amplification; and molecular analyses for recurrent mutations in 15 cancer genes including AKT-1, EGFR, PIK3CA, and TP53 on 54 cases of apocrine-eccrine carcinomas. They include 10 apocrine carcinomas, 7 eccrine carcinomas, 9 aggressive digital papillary adenocarcinomas, 10 hidradenocarcinomas, 11 porocarcinomas, 1 adenoid cystic carcinoma, 4 malignant chondroid syringomas, 1 malignant spiradenoma, and 1 malignant cylindroma. AR, ER, PR, EGFR and HER2 expression was seen in 36% (19/53), 27% (14/51), 16% (8/51), 85% (44/52) and 12% (6/52), respectively. Polysomy or trisomy of EGFR was detected by FISH in 30% (14/46). Mutations of AKT-1, PIK3CA, and TP53 were detected in 1, 3, and 7 cases, respectively (11/47, 23%). Additional investigation regarding the potential treatment of rare cases of apocrine-eccrine carcinomas with PI3K/Akt/mTOR pathway inhibitors, currently in clinical testing, may be of clinical interest.

Molecular Markers with Predictive and Prognostic Relevance in Lung Cancer

Lung cancer accounts for the majority of cancer-related deaths worldwide of which non-small-cell lung carcinoma alone takes a toll of around 85%. Platinum-based therapy is the stronghold for lung cancer at present. The discovery of various molecular alterations that underlie lung cancer has contributed to the development of specifically targeted therapies employing specific mutation inhibitors. Targeted chemotherapy based on molecular profiling has shown great promise in lung cancer treatment. Various molecular markers with predictive and prognostic significance in lung cancer have evolved as a result of advanced research. Testing of EGFR and Kras mutations is now a common practice among community oncologists, and more recently, ALK rearrangements have been added to this group. This paper discusses various predictive and prognostic markers that are being investigated and have shown significant relevance which can be exploited for targeted treatment in lung cancer.

HER2 amplification: a potential mechanism of acquired resistance to EGFR inhibition in EGFR-mutant lung cancers that lack the second-site EGFRT790M mutation

EGF receptor (EGFR)-mutant lung cancers eventually become resistant to treatment with EGFR tyrosine kinase inhibitors (TKI). The combination of EGFR-TKI afatinib and anti-EGFR antibody cetuximab can overcome acquired resistance in mouse models and human patients. Because afatinib is also a potent HER2 inhibitor, we investigated the role of HER2 in EGFR-mutant tumor cells. We show in vitro and in vivo that afatinib plus cetuximab significantly inhibits HER2 phosphorylation. HER2 overexpression or knockdown confers resistance or sensitivity, respectively, in all studied cell line models. FISH analysis revealed that HER2 was amplified in 12% of tumors with acquired resistance versus only 1% of untreated lung adenocarcinomas. Notably, HER2 amplification and EGFR(T790M) were mutually exclusive. Collectively, these results reveal a previously unrecognized mechanism of resistance to EGFR-TKIs and provide a rationale to assess the status and possibly target HER2 in EGFR-mutant tumors with acquired resistance to EGFR-TKIs.

Guidelines for biomarker testing in advanced non-small-cell lung cancer. A national consensus of the Spanish Society of Medical Oncology (SEOM) and the Spanish Society of Pathology (SEAP)

Patients with advanced non-small-cell lung cancer (NSCLC) carrying epidermal growth factor receptor (EGFR) mutations can now have specific treatment based on the result of biomarker analysis and patients with rearrangements of the anaplastic lymphoma kinase (ALK) gene will probably soon be able to. This will give them better quality of life and progression-free survival than conventional chemotherapy. This consensus statement was conceived as a joint initiative of the Spanish Society of Medical Oncology (SEOM) and the Spanish Society of Pathology (SEAP), and makes diagnostic and treatment recommendations for advanced NSCLC patients based on the scientific evidence on biomarker use. It therefore provides an opportunity to improve healthcare efficiency and resource use, which will undoubtedly benefit these patients. Although this field is in continuous evolution, at present, with the available data, this panel of experts recommends that all patients with advanced NSCLC of non-squamous cell subtype, or non-smokers regardless of the histological subtype, should be tested for EGFR gene mutations within a maximum of 7 days from the pathological diagnosis. Involved laboratories must participate in external quality control programmes. In contrast, ALK gene rearrangements should only be tested in the context of a clinical trial, although the promising data obtained will certainly justify in the near future its routine testing in patients with no EGFR mutations. Lastly, routine testing for other molecular abnormalities is not considered necessary in the current clinical practice.

Functional analysis of receptor tyrosine kinase mutations in lung cancer identifies oncogenic extracellular domain mutations of ERBB2

We assessed somatic alleles of six receptor tyrosine kinase genes mutated in lung adenocarcinoma for oncogenic activity. Five of these genes failed to score in transformation assays; however, novel recurring extracellular domain mutations of the receptor tyrosine kinase gene ERBB2 were potently oncogenic. These ERBB2 extracellular domain mutants were activated by two distinct mechanisms, characterized by elevated C-terminal tail phosphorylation or by covalent dimerization mediated by intermolecular disulfide bond formation. These distinct mechanisms of receptor activation converged upon tyrosine phosphorylation of cellular proteins, impacting cell motility. Survival of Ba/F3 cells transformed to IL-3 independence by the ERBB2 extracellular domain mutants was abrogated by treatment with small-molecule inhibitors of ERBB2, raising the possibility that patients harboring such mutations could benefit from ERBB2-directed therapy.

Dysfunctions associated with methylation, microRNA expression and gene expression in lung cancer

Integrating high-throughput data obtained from different molecular levels is essential for understanding the mechanisms of complex diseases such as cancer. In this study, we integrated the methylation, microRNA and mRNA data from lung cancer tissues and normal lung tissues using functional gene sets. For each Gene Ontology (GO) term, three sets were defined: the methylation set, the microRNA set and the mRNA set. The discriminating ability of each gene set was represented by the Matthews correlation coefficient (MCC), as evaluated by leave-one-out cross-validation (LOOCV). Next, the MCCs in the methylation sets, the microRNA sets and the mRNA sets were ranked. By comparing the MCC ranks of methylation, microRNA and mRNA for each GO term, we classified the GO sets into six groups and identified the dysfunctional methylation, microRNA and mRNA gene sets in lung cancer. Our results provide a systematic view of the functional alterations during tumorigenesis that may help to elucidate the mechanisms of lung cancer and lead to improved treatments for patients.

Diminished functional role and altered localization of SHP2 in non-small cell lung cancer cells with EGFR-activating mutations

Non-small cell lung cancer (NSCLC) cells harboring activating mutations of the epidermal growth factor receptor (EGFR) tend to display elevated activity of several survival signaling pathways. Surprisingly, these mutations also correlate with reduced phosphorylation of ERK and SHP2, a protein tyrosine phosphatase required for complete ERK activation downstream of most receptor tyrosine kinases. As ERK activity influences cellular response to EGFR inhibition, altered SHP2 function could have a role in the striking response to gefitinib witnessed with EGFR mutation. Here, we demonstrate that impaired SHP2 phosphorylation correlates with diminished SHP2 function in NSCLC cells expressing mutant, versus wild-type, EGFR. In NSCLC cells expressing wild-type EGFR, SHP2 knockdown decreased ERK phosphorylation, basally and in response to gefitinib, and increased cellular sensitivity to gefitinib. In cells expressing EGFR mutants, these effects of SHP2 knockdown were less substantial, but the expression of constitutively active SHP2 reduced cellular sensitivity to gefitinib. In cells expressing EGFR mutants, which do not undergo efficient ligand-mediated endocytosis, SHP2 was basally associated with GRB2-associated binder 1 (GAB1) and EGFR, and SHP2's presence in membrane fractions was dependent on EGFR activity. Whereas EGF promoted a more uniform intracellular distribution of initially centrally localized SHP2 in cells expressing wild-type EGFR, SHP2 was basally evenly distributed and did not redistribute in response to EGF in cells with EGFR mutation. Thus, EGFR mutation may promote association of a fraction of SHP2 at the plasma membrane with adapters that promote SHP2 activity. Consistent with this, SHP2 immunoprecipitated from cells with EGFR mutation was active, and EGF treatment did not change this activity. Overall, our data suggest that a fraction of SHP2 is sequestered at the plasma membrane in cells with EGFR mutation in a way that impedes SHP2's ability to promote ERK activity and identify SHP2 as a potential target for co-inhibition with EGFR in NSCLC.

Recent understanding of the molecular mechanisms for the efficacy and resistance of EGF receptor-specific tyrosine kinase inhibitors in non-small cell lung cancer

INTRODUCTION

The epidermal growth factor receptor (EGFR) and its family members are involved in many aspects of tumor biological processes. Aberrant activation of the EGFR tyrosine kinase by mutations or protein overexpression is observed in various types of human cancer, including lung cancer. EGFR tyrosine kinase inhibitors (EGFR-TKIs), such as gefitinib and erlotinib, are highly effective in lung cancer patients who harbor active mutations in the EGFR gene. However, patients who are initially sensitive to EGFR-TKIs eventually relapse within few years.

AREAS COVERED

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer and is associated with a high frequency of EGFR mutations. This review describes the EGFR mutations that determine the sensitivity to EGFR-TKIs and the current understanding of the molecular mechanisms of acquired resistance to EGFR-TKIs in NSCLC. Furthermore, the authors describe recent strategies developed to overcome acquired resistance using second-generation EGFR-TKIs and combination therapies with several molecular-targeting drugs.

EXPERT OPINION

Although recent findings have contributed to our understanding of the mechanism of acquired resistance and helped the development of novel strategies to overcome such resistance, the underlying mechanisms are complex and additional research is necessary to develop effective therapeutic strategies for individual patients with lung cancer.

Prevalence, clinicopathologic associations, and molecular spectrum of ERBB2 (HER2) tyrosine kinase mutations in lung adenocarcinomas

PURPOSE

Activating mutations in the tyrosine kinase domain of HER2 (ERBB2) have been described in a subset of lung adenocarcinomas (ADCs) and are mutually exclusive with EGFR and KRAS mutations. The prevalence, clinicopathologic characteristics, prognostic implications, and molecular heterogeneity of HER2-mutated lung ADCs are not well established in U.S. patients.

EXPERIMENTAL DESIGN

Lung ADC samples (N = 1,478) were first screened for mutations in EGFR (exons 19 and 21) and KRAS (exon 2), and negative cases were then assessed for HER2 mutations (exons 19-20) using a sizing assay and mass spectrometry. Testing for additional recurrent point mutations in EGFR, KRAS, BRAF, NRAS, PIK3CA, MEK1, and AKT was conducted by mass spectrometry. ALK rearrangements and HER2 amplification were assessed by FISH.

RESULTS

We identified 25 cases with HER2 mutations, representing 6% of EGFR/KRAS/ALK-negative specimens. Small insertions in exon 20 accounted for 96% (24/25) of the cases. Compared with insertions in EGFR exon 20, there was less variability, with 83% (20/24) being a 12 bp insertion causing duplication of amino acids YVMA at codon 775. Morphologically, 92% (23/25) were moderately or poorly differentiated ADC. HER2 mutation was not associated with concurrent HER2 amplification in 11 cases tested for both. HER2 mutations were more frequent among never-smokers (P < 0.0001) but there were no associations with sex, race, or stage.

CONCLUSIONS

HER2 mutations identify a distinct subset of lung ADCs. Given the high prevalence of lung cancer worldwide and the availability of standard and investigational therapies targeting HER2, routine clinical genotyping of lung ADC should include HER2.

Unlocking Pandora's box: personalising cancer cell death in non-small cell lung cancer

Evasion of apoptosis is a hallmark of tumorigenesis and a recognised cause of multidrug resistance. Over the last decade, insights into how apoptosis might be exploited in non-small cell lung cancer (NSCLC) and how cancer therapeutics might be used to engage apoptotic signalling in a personalised manner have changed markedly. We are now in the wake of a paradigm shift in stratified therapeutic approaches related to NSCLC. At the heart of this shift in thinking is the emerging knowledge that even the most drug-resistant cancers exhibit a functional death pathway and, critically, that this pathway can be efficiently engaged, leading to clinical benefit. This review will summarise current knowledge of mitochondrial apoptotic pathway dysfunction in NSCLC and how the next generation of targeted therapeutics might be used to exploit deficiencies in apoptotic signalling in a personalised manner to improve clinical outcome and predict therapeutic benefit.

p95HER2 truncated form in resected non-small cell lung cancer

INTRODUCTION

Recent studies suggested that p95HER2, the NH2-terminally truncated form of human epidermal growth factor receptor 2 (HER2), could confer resistance to monoclonal antibodies against HER2 (HER2-mab). The aim of this study was to investigate the role of p95HER2 according to HER2 gene copy number (GCN) and HER2 mutation in non-small cell lung cancer (NSCLC).

METHODS

The study included 447 resected NSCLC patients evaluated for P95HER2 status by immunofluorescence. Data were correlated with HER2 GCN evaluated by fluorescence in situ hybridization (FISH) and HER2 mutations. Tumors were scored as positive for p95HER2 expression if any cytoplasmic staining was detected.

RESULTS

P95HER2 was successfully evaluated in 431 patients and was positive (p95HER2+) in 33 (7.6%) cases. HER2 GCN was evaluable in 439 patients, and increased GCN (at least four copies in at least 40% cells) was found in 60 cases, of which 22 (5.0%) displayed gene amplification (GA). Among the 22 patients with HER2 amplification, only one resulted P95HER2+. To further investigate whether the receptor is truncated in presence of gene mutation, in addition to the study cohort, we analyzed p95HER2 status in eight NSCLC samples harboring HER2 mutation, and only one case resulted p95HER2+. In the whole population, p95HER2- patients had numerically higher risk of death than p95HER2+ (hazard ratio = 1.4, p = 0.2). No difference in survival was observed between patients with or without HER2 GA (median 38 versus 41 months, p = 0.46). HER2 GA was significantly associated with EGFR and MET GA, with no effect on survival.

CONCLUSIONS

HER2 truncation and HER2 increased GCN are not prognostic in resected NSCLC. P95HER2 is a very rare event in individuals displaying HER2 gene amplification or mutation.

A targeted enzyme approach to sensitization of tyrosine kinase inhibitor-resistant breast cancer cells

Gefitinib is an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) of potential use in patients with breast cancer. Unfortunately, in clinical studies, gefitinib is often ineffective indicating that resistance to EGFR inhibitors may be a common occurrence in cancer of the breast. EGFR has been shown to be overexpressed in breast cancer, and in particular remains hyperphosphorylated in cell lines such as MDA-MB-468 that are resistant to EGFR inhibitors. Here, we investigate the cause of this sustained phosphorylation and the molecular basis for the ineffectiveness of gefitinib. We show that reactive oxygen species (ROS), known to damage cellular macromolecules and to modulate signaling cascades in a variety of human diseases including cancers, appear to play a critical role in mediating EGFR TKI-resistance. Furthermore, elimination of these ROS through use of a cell-penetrating catalase derivative sensitizes the cells to gefitinib. These results suggest a new approach for the treatment of TKI-resistant breast cancer patients specifically, the targeting of ROS and attendant downstream oxidative stress and their effects on signaling cascades.

A mammary stem cell population identified and characterized in late embryogenesis reveals similarities to human breast cancer

Gene expression signatures relating mammary stem cell populations to breast cancers have focused on adult tissue. Here, we identify, isolate, and characterize the fetal mammary stem cell (fMaSC) state since the invasive and proliferative processes of mammogenesis resemble phases of cancer progression. fMaSC frequency peaks late in embryogenesis, enabling more extensive stem cell purification than achieved with adult tissue. fMaSCs are self-renewing, multipotent, and coexpress multiple mammary lineage markers. Gene expression, transplantation, and in vitro analyses reveal putative autocrine and paracrine regulatory mechanisms, including ErbB and FGF signaling pathways impinging on fMaSC growth. Expression profiles from fMaSCs and associated stroma exhibit significant similarities to basal-like and Her2+ intrinsic breast cancer subtypes. Our results reveal links between development and cancer and provide resources to identify new candidates for diagnosis, prognosis, and therapy.

Intrinsic and acquired resistance to HER2-targeted therapies in HER2 gene-amplified breast cancer: mechanisms and clinical implications

Approximately 25% of human breast cancers overexpress the HER2 (ErbB2) proto-oncogene, which confers a more aggressive tumor phenotype and associates with a poor prognosis in patients with this disease. Two approved therapies targeting HER2, the monoclonal antibody trastuzumab and the tyrosine kinase inhibitor lapatinib, are clinically active against this type of breast cancer. However, a significant fraction of patients with HER2+ breast cancer treated with these agents eventually relapse or develop progressive disease. This suggests that tumors acquire or possess intrinsic mechanisms of resistance that allow escape from HER2 inhibition. This review focuses on mechanisms of intrinsic and/or acquired resistance to HER2-targeted therapies that have been identified in preclinical and clinical studies. These mechanisms involve alterations to HER2 itself, coexpression or acquisition of bypass signaling through other receptor or intracellular signaling pathways, defects in mechanisms of cell cycle regulation or apoptosis, and host factors that may modulate drug response. Emerging clinical evidence already suggests that combinations of therapies targeting HER2 as well as these resistance pathways will be effective in overcoming or preventing resistance.

New developments in the treatment of HER2-positive breast cancer

Approximately 20%-30% of metastatic breast cancers show increased expression of the human epidermal growth factor receptor-2 (HER2) tyrosine kinase. Two HER2-specific therapies are currently approved for clinical treatment of patients with HER2-overexpressing metastatic breast cancer. Trastuzumab is a monoclonal antibody against HER2 and is approved for first-line treatment of HER2-positive metastatic breast cancer. Lapatinib is a small molecule dual inhibitor of epidermal growth factor receptor and HER2 tyrosine kinases, and is approved for trastuzumab-refractory disease. Although trastuzumab is a highly effective therapy for patients with HER2-overexpressing metastatic breast cancer, a significant number of patients in the initial clinical trials of trastuzumab monotherapy showed resistance to trastuzumab-based therapy. Further, among those who did respond, the initial trials indicated that the median time to progression was less than 1 year. Similarly, lapatinib is effective in a subset of trastuzumab-refractory cases, but the majority of patients display resistance. This review discusses the multiple molecular mechanisms of resistance that have been proposed in the literature. In addition, novel agents that are being tested for efficacy against HER2-positive breast cancer, including the antibodies pertuzumab and trastuzumab-DM1 and the immunotoxin affitoxin, are reviewed. The introduction of trastuzumab has revolutionized the clinical care of patients with HER2-positive metastatic breast cancer and has resulted in dramatic reductions in recurrences of early-stage HER2-positive breast cancer. The development and implementation of gene- and protein-based assays that measure potential molecular predictors of trastuzumab resistance will allow individualization of HER2-targeted therapeutic approaches, and may ultimately improve treatment of HER2-positive breast cancer.

CCL2 mediates cross-talk between cancer cells and stromal fibroblasts that regulates breast cancer stem cells

Cancer stem cells (CSC) play critical roles in cancer initiation, progression, and therapeutic refractoriness. Although many studies have focused on the genes and pathways involved in stemness, characterization of the factors in the tumor microenvironment that regulate CSCs is lacking. In this study, we investigated the effects of stromal fibroblasts on breast cancer stem cells. We found that compared with normal fibroblasts, primary cancer-associated fibroblasts (CAF) and fibroblasts activated by cocultured breast cancer cells produce higher levels of chemokine (C-C motif) ligand 2 (CCL2), which stimulates the stem cell-specific, sphere-forming phenotype in breast cancer cells and CSC self-renewal. Increased CCL2 expression in activated fibroblasts required STAT3 activation by diverse breast cancer-secreted cytokines, and in turn, induced NOTCH1 expression and the CSC features in breast cancer cells, constituting a cancer-stroma-cancer signaling circuit. In a xenograft model of paired fibroblasts and breast cancer tumor cells, loss of CCL2 significantly inhibited tumorigenesis and NOTCH1 expression. In addition, upregulation of both NOTCH1 and CCL2 was associated with poor differentiation in primary breast cancers, further supporting the observation that NOTCH1 is regulated by CCL2. Our findings therefore suggest that CCL2 represents a potential therapeutic target that can block the cancer-host communication that prompts CSC-mediated disease progression.

Nuclear translocation of type I transforming growth factor β receptor confers a novel function in RNA processing

Signaling of transforming growth factor β (TGF-β) is redirected in cancer to promote malignancy, but how TGF-β function is altered in a transformed cell is not fully understood. We investigated TGF-β signaling by profiling proteins that differentially bound to type I TGF-β receptor (TβRI) in nontransformed, HER2-transformed, and HER2-negative breast cancer cells using immunoprecipitation followed by protein identification. Interestingly, several nuclear proteins implicated in posttranscriptional RNA processing were uniquely identified in the TβRI coprecipitates from HER2-transformed cells. Ligand-inducible nuclear translocation of TβRI was observed only in transformed cells, and the translocation required importin β1, nucleolin, and Smad2/3. This trafficking was dependent on the high Ran GTPase activity resulting from oncogenic transformation. In the nucleus, TβRI associated with purine-rich RNA sequences in a synergistic manner with the RNA-binding factor hnRNP A1. We further found that nuclear translocation of TβRI specifically induced epidermal growth factor receptor (EGFR) transcript isoform c, which encodes a soluble EGFR protein, through alternative splicing or 3'-end processing. Our study confirms a cancer-specific nuclear translocation of TβRI and demonstrates its potential function in regulating nuclear RNA processing, as well as a novel gain-of-function mechanism of TGF-β signaling in cancer.

Thorsheim H, Lockman J, Gril B, Hua E, Palmieri D, Polli JW, Castellino S, Rubin SD, Lockman PR, Steeg PS, Smith QR. Lapatinib distribution in HER2 overexpressing experimental brain metastases of breast cancer

PURPOSE

Lapatinib, a small molecule EGFR/HER2 inhibitor, partially inhibits the outgrowth of HER2+ brain metastases in preclinical models and in a subset of CNS lesions in clinical trials of HER2+ breast cancer. We investigated the ability of lapatinib to reach therapeutic concentrations in the CNS following (14)C-lapatinib administration (100 mg/kg p.o. or 10 mg/kg, i.v.) to mice with MDA-MD-231-BR-HER2 brain metastases of breast cancer.

METHODS

Drug concentrations were determined at differing times after administration by quantitative autoradiography and chromatography.

RESULTS

(14)C-Lapatinib concentration varied among brain metastases and correlated with altered blood-tumor barrier permeability. On average, brain metastasis concentration was 7-9-fold greater than surrounding brain tissue at 2 and 12 h after oral administration. However, average lapatinib concentration in brain metastases was still only 10-20% of those in peripheral metastases. Only in a subset of brain lesions (17%) did lapatinib concentration approach that of systemic metastases. No evidence was found of lapatinib resistance in tumor cells cultured ex vivo from treated brains.

CONCLUSIONS

Results show that lapatinib distribution to brain metastases of breast cancer is partially restricted and blood-tumor barrier permeability is a key component of lapatinib therapeutic efficacy which varies between tumors.

Clinical activity of afatinib (BIBW 2992) in patients with lung adenocarcinoma with mutations in the kinase domain of HER2/neu

Human epidermal growth factor receptor (HER)2/neu kinase domain mutations are found in approximately 1-4% of lung adenocarcinomas with a similar phenotype to tumors with epidermal growth factor receptor (EGFR) mutations. Afatinib is a potent irreversible ErbB family blocker. We determined the tumor genomic status of the EGFR and HER2 genes in non- or light smokers with lung adenocarcinoma in patients who were entered into an exploratory Phase II study with afatinib. Five patients with a non-smoking history and metastatic lung adenocarcinomas bearing mutations in the kinase domain of HER2 gene were identified, three of which were evaluable for response. Objective response was observed in all three patients, even after failure of other EGFR- and/or HER2-targeted treatments; the case histories of these patients are described in this report. These findings suggest that afatinib is a potential novel treatment option for this subgroup of patients, even when other EGFR and HER2 targeting treatments have failed.

Normal morphogenesis of epithelial tissues and progression of epithelial tumors

Epithelial cells organize into various tissue architectures that largely maintain their structure throughout the life of an organism. For decades, the morphogenesis of epithelial tissues has fascinated scientists at the interface of cell, developmental, and molecular biology. Systems biology offers ways to combine knowledge from these disciplines by building integrative models that are quantitative and predictive. Can such models be useful for gaining a deeper understanding of epithelial morphogenesis? Here, we take inventory of some recurring themes in epithelial morphogenesis that systems approaches could strive to capture. Predictive understanding of morphogenesis at the systems level would prove especially valuable for diseases such as cancer, where epithelial tissue architecture is profoundly disrupted.

Novel therapeutic targets in non-small cell lung cancer

The development of personalized medicine with a focus on novel targeted therapies has supplanted the one-size-fits-all approach to the treatment of many cancers, including non-small cell lung cancer. Targeted therapies, if given to a patient subpopulation enriched by the presence of relevant molecular targets, can often abrogate cell signaling that perpetuates cancer progression. Critical targets activating procancer pathways include, but are not limited to, epidermal growth factor receptor (EGFR), hepatocyte growth factor receptor (MET), vascular endothelial growth factor (VEGF), VEGF receptor, GTPase KRAS (KRAS), receptor tyrosine protein kinase erbB-2 (HER2), echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK), phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha isoform (PIK3CA), serine/threonine-protein kinase B-raf (BRAF), and insulin-like growth factor 1 receptor (IGF-1R). Some target-directed therapies, such as epidermal growth factor receptor tyrosine kinase inhibitors and anti-VEGF monoclonal antibody, have already been approved for clinical use. Others, such as those targeted to MET, VEGFR, HER2, PIK3CA, and IGF-1R, are in clinical testing. This review describes molecular targets in non-small cell lung cancer that are in development or being clinically applied and their implications for developing novel anticancer therapies for this previously refractory malignancy.

Targetable "driver" mutations in non small cell lung cancer

Lung cancer remains the leading cause of cancer-related mortality in the world despite advances in the field of cancer therapeutics. Traditional treatment with empirically chosen cytotoxic chemotherapeutic agents, have given small, but real survival benefits. Recent advances and insights into molecular pathogenesis of lung cancers have provided some novel molecular targets, offering newer strategies and agents that are tumor specific. Studies have identified mutations in specific genes that are involved in driving the development of lung cancer and so it is important to subsequently target them with specific drugs thus changing paradigms of management of this type of cancer. Recently, Lung Cancer Mutation Consortium (LCMC) has identified at least one of the many recognized "driver mutations" in nearly two thirds of the patients with advanced cancer. This study suggests that identification of driver mutations can help in molecular targeted therapeutics and in addition supplant tumor histology in guiding treatment decisions, identifying subset of patients who may benefit therapy. This review focuses on these mutations identified in specific genes serving as "drivers" of lung tumorigenesis and suggests that clear promise for the future of lung cancer treatment is indeed personalized therapy with drugs chosen according to the patient mutation profile. Most clinically relevant translational advances made in genes involved in lung tumorigenesis namely EML4-ALK fusions, HER2, PIK3CA, AKT, BRAF, MAP2K1, MET mutations and amplifications along with the well established EGFR and KRAS mutations are discussed in the context of NSCLCs. These studies emphasize the need for treatment management based on mutation profile along with routine histology based classification of these tumors in future for a directed therapy and thus a better therapeutic outcome.

EGFR-mutated oncogene-addicted non-small cell lung cancer: current trends and future prospects

Non-small cell lung cancer (NSCLC) tumours with certain mutations in the epidermal growth factor receptor (EGFR) tyrosine kinase have been termed 'oncogene addicted' to reflect their dependence on EGFR-mediated pro-survival signalling and their high susceptibility to apoptosis induced by EGFR tyrosine kinase inhibitors (EGFR-TKIs, e.g. gefitinib and erlotinib). The most common mutations (L858R and exon 19 deletions) predict an improved clinical response to first-line oral EGFR-TKIs compared with standard platinum-based chemotherapy in patients with advanced NSCLC. Moreover, these mutations are also prognostic of a relatively indolent course of disease, regardless of treatment, as compared with classical NSCLC. Treatment strategies for oncogene-addicted NSCLC are therefore distinct from those for non-oncogene addicted NSCLC, and will depend on the specific genetic mutation present.

The genomics of lung adenocarcinoma: opportunities for targeted therapies

Standard cytotoxic chemotherapy is effective for some cancers, but for many others, available treatments offer only a limited survival benefit. Lung adenocarcinoma is one such cancer, responsible for approximately half of lung cancer deaths each year. Development of targeted therapies is thought to hold the most promise for successfully treating this disease, but a targeted approach is dependent on understanding the genomic state of the tumor cells. Exon-directed sequencing of large numbers of lung adenocarcinoma tumor samples has provided an initial low-resolution image of the somatic mutation profile of these tumors. Such cancer sequencing studies have confirmed the high frequency of TP53 and KRAS mutations in lung adenocarcinoma, have found inactivating mutations in known tumor suppressor genes not previously associated with lung adenocarcinoma, and have identified oncogenic mutations of EGFR upon which the first targeted therapy for lung adenocarcinoma patients was based. Additional candidate oncogenes await functional validation. It is anticipated that upcoming whole-exome and whole-genome lung adenocarcinoma sequencing experiments will reveal a more detailed landscape of somatic mutations that can be exploited for therapeutic purposes.