Improvement in the clinical outcome of lung cancer is likely to be achieved by identification of the molecular events that underlie its pathogenesis. Here we show that a small inversion within chromosome 2p results in the formation of a fusion gene comprising portions of the echinoderm microtubule-associated protein-like 4 (EML4) gene and the anaplastic lymphoma kinase (ALK) gene in non-small-cell lung cancer (NSCLC) cells. Mouse 3T3 fibroblasts forced to express this human fusion tyrosine kinase generated transformed foci in culture and subcutaneous tumours in nude mice. The EML4-ALK fusion transcript was detected in 6.7% (5 out of 75) of NSCLC patients examined; these individuals were distinct from those harbouring mutations in the epidermal growth factor receptor gene. Our data demonstrate that a subset of NSCLC patients may express a transforming fusion kinase that is a promising candidate for a therapeutic target as well as for a diagnostic molecular marker in NSCLC.
Retinoids have a reputation for being both detrimental and beneficial: they are teratogens, but they also have tumour-suppressive capacity. Cell biology and genetics have significantly improved our understanding of the mechanisms that underlie the anti-proliferative action of retinoids. Recent elucidation of the pathways that are activated by retinoids will help us to exploit the beneficial aspects of this powerful class of compounds for cancer therapy and prevention.
The genome of a subset of non-small-cell lung cancers (NSCLC) harbors a small inversion within chromosome 2 that gives rise to a transforming fusion gene, EML4-ALK, which encodes an activated protein tyrosine kinase. Although breakpoints within EML4 have been identified in introns 13 and 20, giving rise to variants 1 and 2, respectively, of EML4-ALK, it has remained unclear whether other isoforms of the fusion gene are present in NSCLC cells. We have now screened NSCLC specimens for other in-frame fusion cDNAs that contain both EML4 and ALK sequences. Two slightly different fusion cDNAs in which exon 6 of EML4 was joined to exon 20 of ALK were each identified in two individuals of the cohort. Whereas one cDNA contained only exons 1 to 6 of EML4 (variant 3a), the other also contained an additional 33-bp sequence derived from intron 6 of EML4 (variant 3b). The protein encoded by the latter cDNA thus contained an insertion of 11 amino acids between the EML4 and ALK sequences of that encoded by the former. Both variants 3a and 3b of EML4-ALK exhibited marked transforming activity in vitro as well as oncogenic activity in vivo. A lung cancer cell line expressing endogenous variant 3 of EML4-ALK underwent cell death on exposure to a specific inhibitor of ALK catalytic activity. These data increase the frequency of EML4-ALK-positive NSCLC tumors and bolster the clinical relevance of this oncogenic kinase.
Selective small-molecule kinase inhibitors have emerged over the past decade as an important class of anti-cancer agents, and have demonstrated impressive clinical efficacy in several different diseases, including relatively common malignancies such as breast and lung cancer. However, clinical benefit is typically limited to a fraction of treated patients. Genomic features of individual tumours contribute significantly to such clinical responses, and these seem to vary tremendously across patients. Additional factors, including pharmacogenomics, the tumour microenvironment and rapidly acquired drug resistance, also contribute to the clinical sensitivity of various cancers, and should be considered and applied in the development and use of new kinase inhibitors.
A subset (1% to 5%) of non-small-cell lung carcinomas harbors the EML4-ALK fusion gene. Data from previous studies on the histomorphology of ALK-rearranged lung cancer are inconsistent, and the specific histologic parameters that characterize this subset and how accurately such parameters predict underlying ALK abnormality remain uncertain. To answer these questions, we performed a comprehensive histologic analysis of 54 surgically resected, extensively sampled ALK-rearranged lung carcinomas and compared them with 100 consecutive resections of ALK-wild-type lung cancers. All 54 cases showed at least a focal adenocarcinoma component, and 3 and 2 cases had additional squamous and sarcomatoid differentiation, respectively. Solid or acinar growth pattern, cribriform structure, presence of mucous cells (signet-ring cells or goblet cells), abundant extracellular mucus, lack of lepidic growth, and lack of significant nuclear pleomorphism were more common in ALK-positive cancers. Two recognizable constellations of findings, a solid signet-ring cell pattern and a mucinous cribriform pattern, were present at least focally in the majority (78%) of ALK-positive tumors, but were rare (1%) in ALK-negative tumors. Multivariate analysis showed that a combination of these 2 patterns was the most powerful histologic indicator of ALK rearrangement. Characteristic histologies were present both in primary sites and in metastases. Thus, histologic findings may help to identify cases for ALK testing. However, none of the histologic parameters were completely sensitive or specific to ALK rearrangement, and histomorphology should not replace confirmatory molecular or immunohistochemical studies. ALK-positive cancers commonly showed coexpression of thyroid transcription factor-1 and p63, and its significance is currently unclear.
The Ras proteins are pivotal regulators of cellular proliferation, differentiation, motility, and apoptosis. Mutations on the K-ras gene have been found in 20%-30% of non-small-cell lung cancers and are believed to play a key role in this malignancy. Herein, we review the complex biochemical mechanisms through which K-ras exerts its cellular effects and the results from studies designed to evaluate the clinical importance of K-ras in patients with lung cancer. Since the demonstration of K-ras mutation as a negative prognostic marker 2 decades ago, 8 studies have supported this finding, but an equal number have failed to confirm this. There are also conflicting data for K-ras as a predictor of resistance to chemotherapy and radiation therapy. Progress has been hampered by relatively small studies, different methods of molecular analysis, and heterogeneity in histologic subtypes, stage, treatment administered, and survival criteria used. However, recent findings among patients treated with adjuvant chemotherapy or epidermal growth factor receptor inhibitors highlight that K-ras might yet be an important biomarker for non-small-cell lung cancer and worthy of further research.
Retinoic acid plays an important role in lung development and differentiation, acting primarily via nuclear receptors encoded by the retinoic acid receptor-beta (RARbeta) gene. Because receptor isoforms RARbeta2 and RARbeta4 are repressed in human lung cancers, we investigated whether methylation of their promoter, P2, might lead to silencing of the RARbeta gene in human lung tumors and cell lines.
Methylation of the P2 promoter from small-cell lung cancer (SCLC) and non-small-cell lung cancer (NSCLC) cell lines and tumor samples was analyzed by the methylation-specific polymerase chain reaction (PCR). Expression of RARbeta2 and RARbeta4 was analyzed by reverse transcription-PCR. Loss of heterozygosity (LOH) was analyzed by PCR amplification followed by electrophoretic separation of PCR products. Statistical differences were analyzed by Fisher's exact test with continuity correction.
The P2 promoter was methylated in 72% (63 of 87) of SCLC and in 41% (52 of 127) of NSCLC tumors and cell lines, and the difference was statistically significant (two-sided P:<.001). By contrast, in 57 of 58 control samples, we observed only the unmethylated form of the gene. Four tumor cell lines with unmethylated promoter regions expressed both RARbeta2 and RARbeta4. Four tumor lines with methylated promoter regions lacked expression of these isoforms, but demethylation by exposure to 5-aza-2'-deoxycytidine restored their expression. LOH at chromosome 3p24 was observed in 100% (13 of 13) of SCLC lines and 67% (12 of 18) of NSCLC cell lines, and the difference was statistically significant (two-sided P: =.028).
Methylation of the RARbeta P2 promoter is one mechanism that silences RARbeta2 and RARbeta4 expression in many lung cancers, particularly SCLC. Chemical demethylation is a potential approach to lung cancer therapy.
The Erb-B family of receptors plays an important role in lung carcinogenesis and tumor development, and EGFR and HER2 are highly expressed in bronchial preneoplasia. In invasive tumors, EGFR are expressed in 50-90%, and mostly in squamous cell carcinomas, but also in adenocarcinomas and large cell carcinomas, while HER2 is less frequently expressed (20-30%) and mostly expressed in adenocarcinomas. Bronchioloalveolar cell carcinomas may present a distinct EGFR profile compared to the other NSCLCs and evidence and consequences are discussed. The genetic mechanisms responsible for overexpression of EGFR and HER2 proteins might be numerous, including gene dosage (overrepresentation or amplification) as well as translational and post-translational mechanisms. However, for EGFR and HER2 there is a positive correlation between gene copy numbers and level of protein expression demonstrated by fluorescence in situ hybridization analysis and immunochemistry. Gene amplification for EGFR and HER2 is demonstrated in only 5-10% of the tumors. The treatment status and therapeutic limitation with trastuzumab (Herceptin) in lung cancer compared to breast cancer is discussed.
Anaplastic lymphoma kinase was first described in 1994 as the NPM-ALK fusion protein that is expressed in the majority of anaplastic large-cell lymphomas. ALK is a receptor protein-tyrosine kinase that was more fully characterized in 1997. Physiological ALK participates in embryonic nervous system development, but its expression decreases after birth. ALK is a member of the insulin receptor superfamily and is most closely related to leukocyte tyrosine kinase (Ltk), which is a receptor protein-tyrosine kinase. Twenty different ALK-fusion proteins have been described that result from various chromosomal rearrangements, and they have been implicated in the pathogenesis of several diseases including anaplastic large-cell lymphoma, diffuse large B-cell lymphoma, and inflammatory myofibroblastic tumors. The EML4-ALK fusion protein and four other ALK-fusion proteins play a fundamental role in the development in about 5% of non-small cell lung cancers. The formation of dimers by the amino-terminal portion of the ALK fusion proteins results in the activation of the ALK protein kinase domain that plays a key role in the tumorigenic process. Downstream signaling from ALK fusion proteins involves the Ras/Raf/MEK/ERK1/2 cell proliferation module and the JAK/STAT cell survival pathway. Furthermore, nearly two dozen ALK activating mutations participate in the pathogenesis of childhood neuroblastomas along with ALK overexpression. The occurrence of oncogenic ALK, particularly in non-small cell lung cancer, has generated considerable interest and effort in developing ALK inhibitors. Currently, crizotinib has been approved by the US Food and Drug Administration for the treatment of ALK-positive non-small cell lung cancer along with an approved fluorescence in situ hybridization kit used for the diagnosis of the disease. The emergence of crizotinib drug resistance with a median occurrence at approximately 10 months after the initiation of therapy has stimulated the development of second-generation drugs for the treatment of non-small cell lung cancer and other disorders. About 28% of the cases of crizotinib resistance are related to nearly a dozen different mutations of ALK in the EML4-ALK fusion protein; the other cases of resistance are related to the upregulation of alternative signaling pathways or to undefined mechanisms. It is remarkable that the EML4-ALK fusion protein was discovered in 2007 and crizotinib was approved for the treatment of ALK-positive non-small cell lung cancer in 2011, which is a remarkably short timeframe in the overall scheme of drug discovery.
Loss of heterozygosity of a segment at 3p21.3 is frequently observed in lung cancer and several other carcinomas. We have identified the Ras-association domain family 1A gene (RASSF1A), which is localized at 3p21.3 in a minimum deletion sequence. De novo methylation of the RASSF1A promoter is one of the most frequent epigenetic inactivation events detected in human cancer and leads to silencing of RASSF1A expression. Hypermethylation of RASSF1A was frequently found in most major types of human tumors including lung, breast, prostate, pancreas, kidney, liver, cervical, thyroid and many other cancers. The detection of RASSF1A methylation in body fluids such as serum, urine, and sputum promises to be a useful marker for early cancer detection. The functional analysis of RASSF1A reveals a potential involvement of this protein in apoptotic signaling, microtubule stabilization, and cell cycle progression.
Non-small-cell lung cancer (NSCLC) has recently been associated with interesting molecular characteristics that have important implications in carcinogenesis and response to targeted therapies. The unsatisfactory treatment outcomes in advanced NSCLC with respect to long-term survival rates may be improved through a better understanding of the molecular etiology of this disease. For instance, several molecular alterations have been defined as "driver mutations," such as mutations in epidermal growth factor receptor (EGFR), Kirsten-rous avian sarcoma (KRAS), and a chromosome 2p inversion producing an EML4-ALK fusion gene (echinoderm microtubule-associated protein-like 4 fused with the anaplastic lymphoma kinase). Other key signaling pathways such as RAS/RAF/MEK, PI3K/AKT/mTOR (mammalian target of rapamycin), mesenchymal-epithelial transition (MET) kinase, LKB1, and insulin-like growth factor 1 (IGF-1) receptor (IGF-1R) have also been identified as novel targets for lung cancer treatment. In this review we focus on the molecular discoveries that have led to the clinical applications and trials of novel targeted agents, including the clinical trials that selectively studied patients who were predicted to achieve the greatest benefit based on the expression of correlative biomarkers.
Lung cancer has become the leading cause of cancer death in many economically well-developed countries. Recent molecular biological studies have revealed that overt lung cancers frequently develop through sequential morphological steps, with the accumulation of multiple genetic and epigenetic alterations affecting both tumor suppressor genes and dominant oncogenes. Cell cycle progression needs to be properly regulated, while cells have built-in complex and minute mechanisms such as cell cycle checkpoints to maintain genomic integrity. Genes in the p16INK4A-RB and p14ARF-p53 pathways appear to be a major target for genetic alterations involved in the pathogenesis of lung cancer. Several oncogenes are also known to be altered in lung cancer, leading to the stimulation of autocrine/paracrine loops and activation of multiple signaling pathways. It is widely acknowledged that carcinogens in cigarette smoke are deeply involved in these multiple genetic alterations, mainly through the formation of DNA adducts. A current understanding of the molecular mechanisms of lung cancer pathogenesis and progression is presented in relation to cigarette smoking, an absolute major risk factor for lung cancer development, by reviewing genetic alterations of various tumor suppressor genes and oncogenes thus far identified in lung cancer, with brief summaries of their functions and regulation.
This study was conducted to evaluate the clinical significance of the localization of epidermal growth factor receptor (EGF-r), transforming growth factor (TGF)-alpha, and erbB-2 in the development, progression and prognosis of squamous cell cancers (SCCs) of the lung.
The localization of EGF-r, TGF-alpha, and erbB-2 was evaluated immunohistochemically in 60 archival specimens of SCC of the lung and in 60 lung specimens without cancer. To clarify the patterns of expression of EGF-r in these tumors, the patterns of expression of EGF-r in cells in culture were monitored after challenging normal human bronchial epithelial and SCC cell lines with either EGF or TGF-alpha at physiological concentrations.
The expression of EGF-r, erbB-2, and TGF-alpha were significantly higher in SCC and associated precancerous lesions than in the normal bronchial epithelium and hyperplastic lesions of noncancer specimens. A statistically significant stepwise increase in expression from uninvolved bronchial epithelium to precancerous lesions to SCC was observed with EGF-r and TGF-alpha. The localization of EGF-r in the cytoplasm (P = 0.04), but not in the membrane (P = 0.20), of SCCs was significantly associated with poor overall survival of subjects. To demonstrate the biological relevance of cytoplasmic expression of EGF-r, we noted that there was a prompt reduction in the membrane expression and a concomitant increase in cytoplasmic expression of EGF-r after adding either EGF or TGF-alpha to the cell culture medium. Overall, the study identified an involvement of EGF-r and TGF-alpha in the development of SCCs. The prognostic importance of EGF-r expression in the cytoplasm of lung cancer probably is an indication of the prognostic importance of trafficking of the EGF-r receptor between the Golgi apparatus and cell membranes and of internalization of EGF-r after an interaction with one of the EGF-r ligands at the cellular membrane surface.
Progress in genetic engineering has made it possible to elucidate the molecular biological abnormalities in lung cancer. Mutations in KRAS and P53 genes, loss of specific alleles, and DNA methylation of the tumor suppressor genes were the major abnormalities investigated between 1980 and the 2000s. In 2004, mutations in the epidermal growth factor receptor (EGFR) gene that cause oncogene addiction were discovered in non-small-cell lung cancers (NSCLCs), especially in adenocarcinomas. Because they are strongly associated with sensitivity to EGFR-tyrosine kinase inhibitors (EGFR-TKIs), a great deal of knowledge has been acquired in regard to both EGFR and other genes in the EGFR family and their downstream genes. Moreover, in 2007 the existence of the echinoderm microtubule-associated protein-like 4 (EML4)-anaplastic lymphoma kinase (ALK) fusion gene was discovered in NSCLC; and the same as EGFR-TKIs, ALK inhibitors are being found to be highly effective in lung cancers that have this translocation. These discoveries graphically illustrate that molecular biological findings are directly linked to the development of clinical oncology and to improving the survival rates of lung cancer patients. Here, we review the remarkable progress in molecular biological knowledge acquired thus far in regard to lung cancer, especially NSCLC, and the future possibilities.
The molecular basis of lung carcinogenesis must be understood more fully and exploited to enhance survival rates of patients suffering from lung cancer. In this review we will discuss the major molecular alterations that occur in lung cancer. Emphasis is placed on alterations that occur early during carcinogenesis since they might be relevant for future screening programs. Finally we will shortly review new approaches that are used to study the molecular pathology of lung cancer and how they can be applied in a clinical setting.
The development and progression of lung cancer is a multistep process characterized by the accumulation of numerous genetic and epigenetic alterations, some of which occur early in the course of disease. In this review, we summarize cytogenetic imbalances and molecular genetic/epigenetic changes seen in human small-cell and non-small-cell lung cancer. Alterations of tumor suppressor genes and oncogenes leading to perturbations of key cell-regulatory and growth-control pathways are highlighted. The translational implications of molecular biomarkers for risk assessment, early detection, and monitoring of chemoprevention trials are discussed.
ALK rearrangement is particularly observed in signet-ring sub-type adenocarcinoma. Since fluorescence in situ hybridization (FISH) is not suitable for mass screening, we aimed to characterize the predictive utility of tumour morphology and ALK immunoreactivity to identify ALK rearrangement, in a primary lung adenocarcinoma dataset enriched for signet-ring morphology, compared with that of other morphology.
7 adenocarcinomas from diagnostic archives reported with signet-ring morphology were assessed and compared with 11 adenocarcinomas without signet-ring features over the same time period. Growth patterns were reviewed, ALK expression was assessed by standard immunohistochemistry using ALK1 clone and Envision detection (Dako), and ALK rearrangement was assessed by FISH (Abbott Molecular). Associations between groups and predictive utility of tumour morphology and ALK expression using FISH as gold standard were calculated.
2 excision lung biopsy cases with pure (100%) signet-ring morphology and solid patterns demonstrated diffuse moderate cytoplasmic ALK immunoreactivity (2+) and harboured ALK rearrangements (p=0.007), unlike 5 mixed-signet-ring and 11 non-signet-ring adenocarcinomas, which showed negative or 1+ immunoreactivity; and did not harbour ALK rearrangements (p>0.1). ALK expression was not associated with ALK copy number. 6 of 7 cases with signet ring morphology stained for TTF-1. Pure signet-ring morphology and moderate ALK expression were both associated with ALK rearranged tumours.
ALK rearrangement is strongly associated with ALK immunoreactivity, and was seen only in tumours with pure signet-ring morphology and solid growth pattern. Tumour morphology, growth pattern and ALK immunoreactivity appear to be good indicators of ALK rearrangement, with TTF-1 positivity aiding in proving primary pulmonary origin.
Lung cancer is one of the most common cancers worldwide and its pathogenesis is closely associated with tobacco smoking. Continuous exposure of smoking carcinogens results in the accumulation of several alterations of tumorigenesis related genes leading to neoplastic bronchial lesions. Lung cancer is divided in two main histological groups, non-small cell lung carcinomas (NSCLCs) and small cell lung carcinomas (SCLCs). It seems that lung tumorigenesis is a multistep process in which a number of genetic events including alterations of oncogenes and tumor suppressor genes have been occurred. Cytogenetic abnormalities in lung cancer are very complex. However, a number of recurrent cytogenetic abnormalities have been identified. Many of these changes are common in both major histological groups of lung cancer while certain chromosomal abnormalities have been correlated with the stage or the grade of the tumors. In addition, several molecular alterations have been constantly found. Some of them are common in different histological subtypes of lung cancer and they appear to play an important role in the pathogenesis of lung cancer. A good understanding of the underlying genetic changes of lung tumorigenesis will provide new perspectives for early diagnosis and screening of high-risk individuals. In addition, a number of genetical prognostic factors have been identified as possibly helpful parameters in the evaluation of lung cancer patients. Further research is required in order to systematically investigate genetical alterations in lung cancer contributing to improvement of lung cancer classification and staging and to development of new molecular targeted therapies.
EML4-ALK fusion genes have been recognized as novel "driver mutations" in a small subset of non-small cell lung cancers (NSCLC). The frequency of EML4-ALK fusions in NSCLC patients who have clinical characteristics related to EGFR mutation remains unknown. We screened 102 Chinese patients with NSCLC based on one or more of the following characteristics: female, no or light smoking history, and adenocarcinoma histology. EML4-ALK fusion genes were identified by RT-PCR, whereas EGFR (Exons 18-21) and KRAS (Exons 1 and 2) mutations were detected by DNA sequencing. Eight specimens (8%) were positive for EML4-ALK fusions, with seven being Variant 1 and one Variant 2. There were 44 (43%) and 17 (16%) patients harboring EGFR and KRAS mutations, respectively. Thirty-one (31%) cases were wild type for EML4-ALK, EGFR, and KRAS mutations. Of the eight patients with EML4-ALK, none had an EGFR mutation, whereas a KRAS mutation was detected in one patient. Histologically, five of the EML4-ALK positive tumors were adenocarcinoma and two were mixed adenosquamous carcinoma; only one was a squamous carcinoma. Our data support the conclusion that the EML4-ALK fusion gene defines a new molecular subset of NSCLC with distinct pathologic features.
Non-small cell lung cancer (NSCLC) accounts for approximately 85% of all lung cancer that is the leading cause of cancer-related mortality worldwide. Several predictive markers have been found in NSCLC patients to date but only a few are currently used for tailored therapy.
PubMed and Web of Science online databases were used to search review and original articles on the most important predictive markers in NSCLC.
EGFR activating mutations (exons 18 to 21) and EML4-ALK rearrangement are clinically important markers able to select NSCLC patients which benefit from EGFR or ALK tyrosine kinase inhibitors (gefitinib, erlotinib, crizotinib). Other markers, such as KRAS mutation, EGFR T790M mutation and C-MET amplification, are responsible for resistance to these inhibitors. Overcoming of this resistance as well as discovery of new potential markers and inhibitors is the main goal of ongoing research and clinical trials in NSCLC.
It is now widely accepted that human carcinogenesis is a multi-step process and phenotypic changes during cancer progression reflect the sequential accumulation of genetic alterations in cells. Thus, in order to understand the process of acquisition of metastatic phenotypes in cancer cells, it is indispensable to identify genes whose alterations accumulate during cancer progression and correlate with metastatic phenotypes of cancer cells. For this reason, we have been searching for genes that are preferentially altered in metastatic lung cancer cells and have activities to regulate their metastatic potentials. In lung cancer, both the p16INK4A/RB and p53 genes are frequently inactivated and are critical determinants for the regulation of cell growth and apoptosis. However, it still remains unclear whether these genes are also involved in the regulation of metastatic potential in lung cancer cells. Recently, we identified a novel myosin family gene, MYO18B, from the chromosome 22q12.1 region which shows frequent loss of heterozygosity in advanced lung cancer, and we found that this gene is inactivated in approximately 50% of lung cancers by deletions, mutations and methylation. Furthermore, restoration of MYO18B expression suppressed anchorage-independent growth of lung cancer cells. Thus, it was indicated that the MYO18B gene is a strong candidate for a metastasis suppressor gene of human lung cancer. Further functional and biological studies of the MYO18B gene will help us understand the molecular pathway of human lung cancer progression.
To investigate the importance of gene amplification and EGFR (epidermal growth factor receptor) and HER2 protein expression during the progression of adenocarcinoma of the lung.
EGFR and HER2 gene amplification was examined in atypical adenomatous hyperplasia (AAH), bronchioloalveolar carcinoma (BAC), and adenocarcinoma with mixed subtypes (MX) by chromogenic in situ hybridisation (CISH), and protein expression was examined by immunohistochemistry using paraffin wax embedded tissues.
EGFR and HER2 gene amplification was found in four and two of 86 cases, respectively, and was detected only in the invasive components of MX. EGFR and HER2 protein expression was seen in 24 and 18 of 86 cases, respectively. EGFR and HER2 proteins were not expressed in AAH but were expressed in one BAC case each. EGFR and HER2 proteins were expressed in 23 and 17 of 55 adenocarcinomas with MX. EGFR and HER2 protein expression was seen more often in the invasive components than in the BAC components of MX, and increased significantly as lesions progressed from AAH to BAC, early MX, and overt MX. Because EGFR and HER2 protein expression was frequently seen without gene amplification, other mechanisms apart from gene amplification may be associated with protein expression.
EGFR and HER2 gene amplification may be a late event and EGFR and HER2 protein expression may be associated with the development of adenocarcinoma of the lung.