Correspondence: Dr Biing-Shiun Huang, Division of Thoracic Surgery, Department of Surgery, Taipei Veterans General Hospital and National Yang-Ming University School of Medicine, no. 201, Section 2, Shih-Pai Road, Taipei 112, Taiwan. Email: huanghhh@ms23.hinet.net
Accepted for publication 3 January 2006.
REVIEW ARTICLE
Targeting epidermal growth factor receptor in lung cancer:
Perspective from the Asia–Pacific region
H Eugene LIU,
1Ken-Hong LIM,
2Ming-Jer HUANG
2and Biing-Shiun HUANG
31Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, 2Division of Hematology and Oncology,
Department of Internal Medicine, Mackay Memorial Hospital and 3Division of Thoracic Surgery, Department of Surgery, Taipei
Veterans General Hospital and National Yang-Ming University School of Medicine, Taipei, Taiwan
Abstract
The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase of the ErbB family that is frequently overexpressed in non-small cell lung cancer (NSCLC), and has been identified as a novel therapeutic target for lung cancer. The development of small molecule EGFR-tyrosine kinase inhibitors (TKI) such as gefitinib and erlotinib has resulted in paradigm shift in the treatment of advanced NSCLC. The impact of EGFR-TKI in the treatment of NSCLC is even greater in Asia–Pacific region because one of the greatest clinical benefits of EGFR-TKI has been seen in patients of East Asian ethnicity. The discovery of somatic mutations in EGFR-tyrosine kinase domain has so far answered some, but not all, of the questions regarding the clinical response to EGFR-TKI in NSCLC. In addition, other molecular profiles such as KRAS mutations have also been found to play an important role in EGFR targeted therapy. In this article, we review EGFR targeted therapy in NSCLC with the focus on perspective from the Asia–Pacific region. Key words: epidermal growth factor receptor, erlotinib, gefitinib, mutation, non-small cell lung carcinoma.
INTRODUCTION
Lung cancer has been the most common cancer in the world since 1985. In 2002, 1.35 million of people worldwide were diagnosed with this disease, and 1.18 million died from it, accounting for 17.6% of all cancer death.1 It is by far the most common cancer in men, with
the highest rates in North America and Europe, fol-lowed by Australia/New Zealand and East Asia. In East Asia, the incidence of lung cancer is highest in China (42.4 per 100 000), followed by Australia/New Zealand (39.1 per 100 000) and Japan (38.1 per 100 000). Sim-ilarly in Taiwan, the incidence of lung cancer, currently secondary to liver cancer, has been rising in the past 10 years. In 2004, lung cancer is the second most mon cause of cancer death in men and the most
com-mon in women. As the mass vaccination program for hepatitis B (HBV), which has been in place since the early 1980s, has significantly decreased the incidence of HBV-related liver cancer, lung cancer is expected to exceed liver cancer as the leading cause of cancer death in the decades to come.2
The incidence and mortality of lung cancer are very much influenced by past exposure of tobacco smoking. Globally, an estimated 85% of lung cancer in men, and 47% of lung cancer in women is related to tobacco smoking. However, in the Asia–Pacific region, the impact of smoking on lung cancer, especially for women, has been less conclusive. For example, in Tai-wan, only 9% of women with lung cancer are smokers, in contrast to more than 70% in Western countries.3 In
terms of the histologic types, adenocarcinoma is seen in 42.1% of lung cancer in men and 73.4% in women. Several factors that might contribute to the increase of lung adenocarcinoma in Asian women include cooking styles and the presence of carcinogenes in cooking oil fumes, the NAT2 fast acetylator genotype and cyto-chrome P4501A1 activity.4,5 How these factors play a
defined, but obviously the pathogenesis of lung cancer in these populations could be different from what has been described in Western countries. Therefore, treat-ment strategies will need to be tailored to the unique pathogenesis in Asia–Pacific region.
In the past, the treatment for advanced lung cancer has been disappointing.6 However, with the
introduc-tion of newer and less toxic agents and improvement of supportive care, treatment with platinum agents in con-junction with either taxane agents, gemcitabine, or vinorelbin has become the standard chemotherapy for advanced lung cancer, reaching an overall survival to approximately 9–10 months.7 Since the cancer growth
requires angiogenesis, strategies targeting molecules critical for angiogenesis have also been devised to improve lung cancer treatment. One of the agents is bevacizumab, a monoclonal antibody against vascular endothelial growth factor, which is crucial for angiogen-esis in cancer. Results from Eastern Clinical Oncology Group (Trial E4599) have shown that the inclusion of bevacizumab to platinum-based chemotherapy has sig-nificantly improved the overall survival of advanced lung cancer to more than one year.8,9 At the same time,
the identification of epidermal growth factor receptor (EGFR), a receptor tyrosine kinase on the lung cancer biology also prompts the development of another class of agents, so-called tyrosine kinase inhibitors (TKI).10
Because EGFR is overexpressed in 40–80% of NSCLC, the enthusiasm of using TKI to inhibit EGFR in lung cancer is inspired by the successful use of imatinib mesy-late, a TKI against BCR/ABL, the hallmark of chronic myelogenous leukemia (CML). Imatinib has revolution-ized the treatment for CML because more than 90% of BCR/ABL(+) CML respond to this agent without signif-icant toxcities.11–13
TARGETING EGFR IN LUNG CANCER
Many lung cancers (40–80%), mainly NSCLC, overex-press EGFR, making it an ideal target for novel thera-pies. Therefore, in the effort to develop more specific and effective treatment, EGFR has been identified as a potential target for lung cancer. The EGFR gene is located in chromosome 7p. EGFR is a 170-kDa receptor tyrosine kinase that dimerizes and then phosphorylates tyrosine residues when specific ligands, such as epider-mal growth factor (EGF), are engaged.14 Phosphorylatedtyrosines then serve as binding sites for multiple down-stream signal molecules critical for cell survival (e.g. PI3K/Akt) and proliferation (e.g. ras/MAPK) (Fig. 1). The overexpression of EGFR in lung cancer is due to (i)
overexpression of EGF through epigenetic mechanisms; (ii) amplification of EGFR; or (iii) constitutive activa-tion of EGFR by mutaactiva-tions.15
USE OF EGFR INHIBITORS IN LUNG
CANCER
Since the early 1990s, investigators studying EGFR in carcinogenesis have been trying to identify compounds that can inhibit its catalytic activity. They found an anilinoquinazoline compound that inhibited tyrosine kinase activity. However, in vivo studies using this com-pound showed that it was rapidly metabolized and required constant dosing, which would be inconvenient in the clinic. Later, a modified compound gefitinib (pre-viously called ZD1839; AstraZeneca) was developed with improved stability and better efficacy, and showed high and sustained blood levels in mice over a 24- h period.16 Gefitinib in a concentration of 5.7 µmol/L after
an oral dose of 200 mg/kg in mice competitively inhibits the binding of ATP to EGFR, blocking EGFR’s tyrosine kinase activity.16 The selectivity of gefitinib has been
demonstrated using different tyrosine kinases. The con-centration required to inhibit the vascular growth factor receptor-KDR or Flt1 is 100 times higher than that needed to inhibit EGFR.17 Gefitinib does not inhibit
other types of kinases, such as serine/threonine kinases, including Raf, MAPK, and MEK1.
Gefitinib has shown great promise in lung cancer in animal studies. In human xenograft tumor models in nude mice, gefitinib alone was given 5 days per week for Figure 1 Schematic diagram of epidermal growth factor receptor signaling pathway
2 successive weeks. At doses of 100 or 150 mg/kg, gefi-tinib can induce partial regressions of xenograft lung cancers.18 When gefitinib was coadministered with
cyto-toxic chemotherapy agents or radiotherapy, additive or even synergistic antitumor activity was achieved in xenograft lung tumors in nude mice.19,20 After the
prom-ising activity of gefitinib in NSCLC was seen in phase I studies,21–23 two randomized, multicenter global and
US-based phase II clinical trials were conducted to compare daily oral doses of 250 mg and 500 mg gefitinib as second- or third-line monotherapy in patients with advanced NSCLC.24,25 The overall response rate in the
global Iressa Dose Evaluation in Advanced Lung Cancer (IDEAL)-1 and in the US-based IDEAL-2 was 18% and 10%, respectively. However, the response rate was 28% in Japanese patients in IDEAL-1, significantly higher than 10% observed in non-Japanese patients in IDEAL-1 and 2.26
Several preclinical reports have shown that EGFR-TKI can enhance the antitumor activity of chemother-apy, especially when gefitinib was combined with cispl-atin, carboplcispl-atin, paclitaxel, and docetaxel- the agents commonly used in lung cancer.27 These results, along
with the good tolerability of profile by EGFR-TKI, pro-vide a rationale for the two subsequent randomized phase III trials for previously untreated patients with advanced NSCLC to receive standard platinum-based chemotherapy, with or without the addition of gefitinib at two doses.28,29 Patients were randomized to receive
either gefitinib (250 mg/day or 500 mg/day) or placebo in combination with cisplatin/gemcitabine (INTACT 1,
n = 1093) or carboplatin/paclitaxel (INTACT 2, n =
1037). Disappointingly, both studies failed to show any differences in response rate, time to progression (TTP), or 1-year or overall survival when gefitinib was added. Even though gefitinib was unable to provide significant survival benefit, it was approved in Japan and South Korea in July 2002 for both second- and third-line ther-apy, and the United States in May 2003 for third-line therapy in advanced NSCLC. Approvals were based on data from the IDEAL 1 and 2 studies, which showed approximately 50% of patients in the IDEAL trials achieved clinical benefit with gefitinib, often associated with symptom relief.24,25 Thereafter, gefitinib was also
approved in many other countries such as Australia, New Zealand, Singapore, and Taiwan. But the use of gefitinib does not come without a price. Although stud-ies in Japanese patients showed higher response rates, they also revealed fatal pulmonary complications.30
Even so, lung cancer patients, being desperate for a cure, are eager to take on a chance that this novel agent might
cure them. Subsequently, a large phase III randomized, placebo-controlled study (ISEL, n = 1692) was initiated to evaluate the effect on survival of gefitinib as second-or third-line treatment fsecond-or patients with locally advanced or metastatic NSCLC.31 Gefitinib failed to
prolong survival in the overall population of patients and those with adenocarcinoma. However, in pre-planned subgroup analyses, gefitinib significantly pro-longed survival in the never-smokers and patients of Asian origin subgroups.
Erlotinib (Tarceva, previously called OSI774; OSI Pharmaceuticals), another EGFR-TKI, was approved by the US Food and Drug Administration in November 2004 for use in lung cancer. Erlotinib, which has equiv-alent efficacy to gefitinib in animal studies, is showing results similar to gefitinib. In athymic nude mice xenograft models, erlotinib has antitumor activity both as monotherapy and in combination with chemothera-pies.32,33 In addition, erlotinib also enhances radiation
response in xenograft models resulting in profound tumor growth inhibition.32 In two phase II studies of
erlotinib, patient enrollment required EGFR-expressing NSCLC or NSCLC with bronchioloalveolar carcinoma (BAC) histology, respectively.34,35 The response rate was
higher when erlotinib was used as a first-line or second-line therapy in NSCLC with BAC subtype.35 Erlotinib
has also been studied in two large phase III front-line clinical trials in combination with chemotherapy. These two studies randomly assigned patients with good per-formance status and previously untreated advanced (stage IIIB/IV) NSCLC to erlotinib 150 mg/d or placebo combined with up to a maximum of 6 cycles of carbo-platin/paclitaxel (the TRIBUTE study; n = 1079) or cis-platin/gemcitabine (TALENT; n = 1172) after which patients continued on erlotinib until disease progres-sion.36,37 The addition of erlotinib to chemotherapy, like
what has been found in gefitinib study, did not improve response rate, time to progression, or survival. It is noteworthy that in these two phase III studies the patients enrolled were not selected based on known prognostic factors especially EGFR expression or BAC histologic subtype used in phase II studies. In addition, after retrospective subset analysis of the TRIBUTE study, mutations in EGFR and in KRAS have been found to have important prognostic impact in advanced NSCLC patients treated with chemotherapy with or without erlotinib.38 The lack of patient selection may
have adversely affected the results of these phase III studies. However, in a phase III randomized, placebo-controlled study involving 731 patients, erlotinib as a single-agent therapy can prolong survival in NSCLC
patients who failed first- or second-line chemotherapy.39
This result will need to be further validated by other studies.
Despite of the promising results in preclinical and early phase studies, anti-EGFR therapy in lung cancer is intriguing in two aspects – the antitumor activity of EGFR inhibitors does not appear to correlate with EGFR expression, and addition of inhibitors to chemo-therapy failed to achieve significant additional survival benefit in large randomized controlled trials. This sug-gests that cancer cells might have evolved multiple path-ways for cell proliferation and survival. Simply blocking EGFR signaling is not enough to halt the cancer. Other possible explanations for lack of additional benefit include the possibility that concurrent administration of chemotherapy and EGFR-TKI are antagonistic in at least a subset of patients treated. Preclinical studies have showed that EGFR-TKI result primarily in a G1 cell cycle arrest in cancer cell lines with wild type EGFR, versus induction of apoptosis in cell lines with mutant EGFR.40 In vitro and in vivo combination studies have
further shown that G1 arrest resulting from pretreat-ment with EGFR-TKI blocks subsequent effects of chemotherapy, and that continuous concurrent ad-ministration of the combination is less effective than intermittent or sequential pulse therapy.41,42 Clinical
studies using alternative ways of combining chemother-apeutic agents with EGFR-TKI in terms of sequences and settings are ongoing.
Currently, there are several small molecule EGFR-TKI under clinical development. These include irrever-sible EGFR inhibitors (e.g. EKB-569, HKI-272), dual EGF/HER2 receptor inhibitors (e.g. lapatinib and BMS-599626), pan-ErbB receptor inhibitors (e.g. CI-1033), and dual EGF/VEGF receptor inhibitors (e.g. ZD6474).43–46 Through the inhibition of EGFR and
other HER receptors or other TK-receptor families, greater antitumor activity may be achieved and promis-ing clinical result has been reported.44
IDENTIFICATION OF EGFR MUTATIONS
IN LUNG CANCER
Although the clinical trials on gefitinib failed to demon-strate any survival advantage, there are sporadic reports of dramatic response on certain patients. The exact rea-sons why those patients respond so well remained elu-sive until the reports in mid-2004 that two groups, using different approaches, first identified the presence of somatic EGFR mutations in NSCLC might correlate with the response to gefitinib.47,48 In the studies by Lynch
et al., they hypothesized that patients with NSCLC who
had striking responses to gefitinib had somatic muta-tions in the EGFR gene that would indicate the essential role of the EGFR signaling pathway in the tumor. They first looked for rearrangements within the extracellular domain of EGFR that are characteristic of gliomas, and none were detected. They then sequenced the entire coding region of EGFR gene in primary lung tumors from patients with a response to gefitinib, from those without a response, and from 25 patients who had never received gefitinib. In another study, Paez et al. initially amplified and sequenced the exons encoding the activa-tion loops of 47 of the 58 human receptor tyrosine kinase genes from genomic DNA from a subset of 58 NSCLC samples. Only three of the lung adenocarcino-mas showed the same heterozygous somatic missense mutations in EGFR. Subsequently, they amplified and sequenced exons 2 through 25 of EGFR in 119 primary NSCLC specimens from patients who had never received gefitinib. Both groups each identified two classes of somatic mutations within the EGFR tyrosine kinase domain of their NSCLC specimens that correlate with clinical response to gefitinib. The first class included missense mutations with amino acid substitu-tions in exon 18 (the p-loop of the kinase domain) or in exon 21 (the activation loop of the kinase domain). The second class involved in-frame deletions within exon 19 that change the structure and spatial orienta-tion of the catalytically important αC-helix of the kinase domain. In vitro functional assays in transient trans-fected Cos-7 cells and lung cancer cell lines showed that these mutant EGFR proteins have enhanced EGF-depen-dent activation and markedly increased sensitivity to gefitinib inhibition.47,48
Several subsequent NSCLC studies have identified more than 29 EGFR mutations among different ethnic groups.49–58 These mutations are thought to be somatic
in origin and most of them are clustered in exon 18–21. They consist of three very different types: in-frame dele-tions, insertion, and missense point mutadele-tions, and are often located in key structural positions in EGFR includ-ing the P-loop, the αC-helix, and the A-loop. In-frame deletions in exon 19, accounting for 44% of all muta-tions, are the most common type of mutamuta-tions, followed by the missense mutations, a single nucleotide substitu-tion L858R, at exon 21 (41% of all mutasubstitu-tions), in-frame insertion at exon 21 (5% of all mutations) and point mutations at exon 18 (4% of all mutations). It is noteworthy that many exon 19 deletions lack amino acids LREA (leucine, arginine, glutamic acid, and ala-nine) at codons 747 through 750.47,49 Interestingly, de
novo double EGFR mutations were also found in a few of patients.49,50,58 Studies on the two most common types
of mutations have shown that these mutations preferen-tially activates antiapoptotic pathways (PI3K/Akt and Jak/Stat), but have less effect on cellular proliferation.59
How lung cancer cells acquire these mutations is still unclear, but it appears to be an early event during car-cinogenesis because the presence of mutations does not correlate with disease stage. If this is true, these muta-tions might arise at the levels of lung progenitor or even stem cells in the airways, making these lung cancer cells ideal targets for EGFR-TKI therapy.
In the initial studies, patients with a dramatic response to gefitinib showed similar profiles: women, patients with BAC or adenocarcinoma, and non-smokers.24,25 Comparing the mutations rates among
different ethnic groups, it is interesting to note that patients with East Asian ethnic background have signif-icantly higher rates of mutations than their Western counterparts (Table 1). In Western countries, the rates of mutations are at most 14% in USA, 7% in Austra-lia, and 4.5% in Italy; while in Asian countries, the mutation rates are significantly higher and could be as higher as 49% in adenocarcinoma. In our series in Taiwan,58 high frequency of EGFR mutations are found
in lung adenocarcinomas, and correlated significantly with female sex, BAC histologic subtype, and non-smokers (Table 2). A similar trend is also observed in Japanese studies. In China, there is female and adeno-carcinoma histology preponderance in lung cancer, but there is no significant difference in EGFR mutations between smokers and non-smokers. The profile of patients with EGFR mutations in Korea is similar to that in China. Whether these differences in characteriz-ing mutation-positive NSCLC are caused by variations in sampling, race, or other unidentified factors requires further investigation.
SIGNIFICANCE OF EGFR MUTATIONS
IN LUNG CANCER PATIENTS IN THE
ASIA–PACIFIC REGION
The high mutation rates in the Asia–Pacific region raise several interesting and critical issues. For cancer biology, the high mutation rates in Asian patients imply a differ-ent biological process during cancer developmdiffer-ent. The likelihood that EGFR mutations arise at the level of pulmonary epithelial progenitors and the concept of targeting cancer stem cells, which have also been iden-tified in lung cancer, suggest that a different strategy might be needed for treating these patients.60 A recent
finding that lung cancer with BAC subtype responds more favorably to conventional therapy than with other pathological types suggests that this group of patient will need a separate treatment strategy.61 Currently,
treatment of lung cancer is based on the pathology (small cells vs non-small cells), stage of the disease, age, and performance status of patients, but not on tumor biology. Studies on lymphoma, leukemia, breast cancer and gastrointestinal stromal tumors have shown that tumor biology greatly affects the treatment outcome. As with breast cancer, the expression pattern of selected genes has been shown to predict the likelihood of distant recurrence and the survival.62 Thus, with the new
infor-mation about EGFR mutations, particularly in the Asia– Pacific region, it may be time to correlate tumor biology with the clinical behavior of lung cancer, to identify new risk factors, and to tailor treatment strategies according to changes at the molecular levels.
The latest information about EGFR mutations appears to be leading us to this direction.63 Patients with
EGFR mutations are more responsive to EGFR-TKI (25
vs 9.1% in patients without mutations), and those with
deletion at exon 19 appear to respond more favorably than those with exon 21 point mutation. Most impor-tant of all, with gefitinib therapy, patients with EGFR mutations have significantly longer survival than those without.52,54 With the relationship between BAC and
EGFR mutations, it requires further studies to under-stand whether patients with EGFR mutations do survive longer by EGFR inhibitors or if they are inherently more responsive to therapy, regardless whether it is by EGFR inhibitors or by conventional chemotherapy, and whether a combination of EGFR inhibitors and chemo-therapy could provide a better control of the disease. Just as small-cell lung cancer has been separated from other types of lung cancer and requires different treat-ment strategies, it might be time to substratify patients with non-small cell lung cancer, not only by conven-tional classification, but also by the new genetic information.
If the latest information on the treatment outcomes of EGFR inhibitors is to be considered in the future, should we routinely screen for EGFR mutations in Asia– Pacific region, and how should these mutations be screened? Most investigators currently rely on direct sequencing to detect mutations, and real-time PCR to quantify gene amplifications; these methodologies are technically more demanding than the conventional pathological examination and can only be performed in selected centers. Furthermore, improvement of the detection method will be necessary before it is widely
T
able 1
EGFR
mutations in different ethnic groups
Country
T
otal
no. of patients No. with mutation
(%) Sex No. with mutation/total (%) p Smoking status No. with mutation/total (%) p Histologic subtype No. with mutation/total (%) p T aiwan (Hsieh), 58 35 17 (48) M 4/17 (23) 0.004 Never smoker 14/21 (66) 0.009 Adenocarcinoma 3/14 (21) 0.009 F 13/18 (72) Smoker 3/14 (21) BAC* 14/21 (66) T aiwan (Huang), 50 101 39 (38.6) M 18/56 (32) NR Never smoker NR NR Adenocarcinoma 38/69 (55) NR F 21/45 (46.6) Smoker Other 1/32 (3) China (W u), 73 135 26 (19.3) M NR/94 NS Never smoker NR NS Adenocarcinoma 25/82 (30) NR F NR/41 Smoker Other 1/53(2) China (Qin), 55 41 10 (24.4) M 6/30 (20) NR Never smoker 6/21 (28.6) NR Adenocarcinoma 7/17 (41.2) NR F 4/11 (36.4) Smoker 4/20 (20) Other 3/24 (12.5) Japan (Kosaka), 49 277 111 (40) M 41/159 (26) < 0.001 Never smoker 76/115 (66) < 0.001 Adenocarcinoma 110/224 (49) < 0.001 F 70/118 (59) Smoker 35/162 (22) Other 1/53 (2) Korea (Han), 52 90 17 (18.9) M 5/54 (9.3) 0.004 Never smoker 11/43 (25.6) 0.12 Adenocarcinoma 14/65 (21.5) 0.38 F 12/36 (33.3) Smoker 6/47 (12.8) Other 3/25 (12) Italy (Marchetti), 51 860 39 (4.5) M 18/748 (2.4) NR Never smoker 23/115 (20) NR Adenocarcinoma 39/375 (10) NR F 21/112 (19) Smoker 16/745 (2) Other 0/485 (0) USA (Shigematsu), 56 80 11 (14) M 3/43 (7) 0.116 Never smoker 7/26 (27) 0.043 Adenocarcinoma 11/44 (25) < 0.001 F 8/37 (22) Smoker 4/54 (7) Other 0/36 (0) Australia (Shigematsu), 56 83 6 (7) M 1/58 (2) 0.013 Never smoker 4/7 (57) < 0.001 Adenocarcinoma 5/36 (14) 0.081 F 5/25 (20) Smoker 2/76 (3) Other 1/47 (2)
BAC, bronchioloalveolar carcinoma; F
, female; M, male; NR, not reported; NS, not signifi
cant. * Includes adenocarcinoma with any
available to clinical practice. As about 95% of muta-tions are clustered in four different exons, it is likely to develop rapid and cost-effective methods to screen out mutations before treatment.64–66
CLONAL SELECTION AND DRUG
RESISTANCE: A DESTINED SCENARIO?
Despite the excitement caused by the dramatic response in patients with EGFR mutations, EGFR-TKI do not provide a cure. Most patients with a good initial response eventually relapse. Studies on CML have dem-onstrated that cancer cells, which are initially sensitive to imatinib develop resistance by acquiring new muta-tions or gene amplification.67 A similar scenario has alsobeen found in gefitinib-resistant lung cancer, in which a second mutation at T790M suppresses inhibition by EGFR inhibitor.68,69 Although the T790M mutation
con-tributes to the resistance in some cases, the underlying mechanisms for resistance in cases lacking the second mutations remain unclear. A recent report using gene expression profiling has identified epithelial membrane protein-1 (EMP-1), as a potential marker for the resis-tance of EGFR inhibitor.70 It is likely that the
up-regu-lation of EMP-1 is caused by drug selection, and that the expression of EMP-1 provides a survival advantage in de novo resistant cases. As EMP-1 is a junctional protein between intracellular microfilaments, and extra-cellular matrix, it also highlights the importance of tumor microenvironment on drug resistance. Another molecular mechanism that correlates with primary resis-tance of lung adenocarcinomas to EGFR-TKI is KRAS
mutations.71 Studies on lung cancer resistant to
EGFR-TKI have shown that mutations in EGFR and KRAS appear to be mutually exclusive. As RAS is also associ-ated with cell adhesion molecules and intracellular actins, its mechanisms with regard to the resistance to EGFR-TKI might also be related to interaction with tumor microenvironment as well.
How can we overcome the resistance to EGFR inhib-itors? Two studies have tried to identify novel com-pounds to block the EGFR signaling in lung cancer harboring T790M mutations.46,72 Whether these new
compounds could be effective for those resistant lung cancers without T790M mutation is still unclear.
CONCLUSIONS
The story of EGFR mutations so far answers some, but not all, of the questions in lung cancer. In fact, it creates more questions than answers, especially in the Asia– Pacific region. The question of why patients in this region have higher rates of EGFR mutation needs to be further elucidated, both because of its therapeutic rele-vant to EGFR-TKI and its potentially critical role in the carcinogenesis of lung cancer. Although EGFR-TKI have been shown to increase survival in advanced NSCLC, the magnitude of benefits is different in dis-tinct patient populations. The greatest clinical benefits of EGFR-TKI have been seen in female patients of East Asia ethnicity, who have never smoked and have adenocarcinoma including adenocarcinoma with BAC features. Thus, it is important that pathologists can routinely report the presence or absence of BAC fea-Table 2 The relationship of EGFR mutations with BAC subtype
Country No. of adenocarcinoma No. of ADC No. of EGFR mutations (%) No. of PBAC No. of EGFR mutations (%) No. of AWBF No. of EGFR mutations (%) p* Taiwan (Hsieh),58 35 14 3 (21) 13 7 (53) 21 14 (66)* 0.009 Taiwan (Huang),50 69 66 38 (57) 3 0 (0) NA NA NA Korea (Han),52 65 55 11 (20) 3 1 (33) 10 3 (30)* 0.44 Japan (Kosaka),49 224 219 107 (48) 5 3 (60) NA NA NA Italy (Marchetti),51 375 289 17 (6) 86 22 (26)* NA NA 0.000002 United States (Shigematsu),56 97 80 11 (13) 7 0 (0) 17 4 (27) NA United States (Lynch),47 22 7 0 (0) NA NA 15 2 (13) NA
ADC, adenocarcinoma other than bronchioloalveolar carcinoma; AWBF, adenocarcinoma with any bronchiolealveolar features including pure bronchioloalveolar carcinomas; BAC, bronchioloalveolar carcinoma; NA, not assessed; PBAC, pure bronchioloalveolar carcinoma. *Compare with adenocarcinoma other than bronchioloalveolar carcinoma.
tures in cases of adenocarcinoma. In addition, NSCLC with unusual clinical manifestations such as those presented with brain metastases, malignant pericardial effusions, or widespread metastases, may also benefit from EGFR-TKI therapy (clinical observations). It is noteworthy that all of these clinical features are associ-ated with EGFR mutations in NSCLC, and EGFR mutation testing in these selected cases may provide important information related to EGFR-TKI therapy. It is also important to establish a standardization of EGFR mutation testing methodology among all the lab-oratories involved. While EGFR targeted therapy has shifted the paradigm of treatment in lung cancer, a meta-analysis of current studies is still necessary to fur-ther clarify its roles. In addition, the development of a decision tree is also needed to indicate criteria under which EGFR-TKI, including its front-line use, is indi-cated. All of these advancements can only be achieved through concerted efforts among basic researchers, clin-ical investigators and epidemiologists throughout the Asia–Pacific region.
REFERENCES
1 Parkin DM, Bray F, Ferlay J, Pisani P. Global cancer sta-tistics, 2002. CA Cancer J Clin 2005; 55: 74–108. 2 Chan CY, Lee SD, Lo KJ. Legend of hepatitis B
vaccina-tion: the Taiwan experience. J Gastroenterol Hepatol 2004; 19: 121–6.
3 Wu PF, Chiang TA, Wang TN et al. Birth cohort effect on lung cancer incidence in Taiwanese women 1981–98. Eur J Cancer 2005; 41: 1170–7.
4 Chiou HL, Wu MF, Chien WP et al. NAT2 fast acetylator genotype is associated with an increased risk of lung cancer among never-smoking women in Taiwan. Cancer Lett 2005; 223: 93–101.
5 Larsen JE, Colosimo ML, Yang IA, Bowman R, Zimmer-man PV, Fong KM. Risk of non-small cell lung cancer and the cytochrome P4501A1 Ile462Val polymorphism. Can-cer Causes Control 2005; 16: 579–85.
6 Belani CP. Non-small-cell lung cancer have we reached a ‘chemotherapy efficacy plateau’? Clin Lung Cancer 2000; 2: 10.
7 Pfister DG, Johnson DH, Azzoli CG et al. American Soci-ety of Clinical Oncology treatment of unresectable non-small-cell lung cancer guideline: update 2003. J Clin Oncol 2004; 22: 330–53.
8 Johnson DH, Fehrenbacher L, Novotny WF et al. Randomized phase II trial comparing bevacizumab plus carboplatin and paclitaxel with carboplatin and paclitaxel alone in previously untreated locally advanced or meta-static non-small-cell lung cancer. J Clin Oncol 2004; 22: 2184–91.
9 Tyagi P. Bevacizumab, when added to paclitaxel/carbopl-atin, prolongs survival in previously untreated patients with advanced non-small-cell lung cancer: preliminary results from the ECOG 4599 trial. Clin Lung Cancer 2005; 6: 276–8.
10 Ciardiello F, Tortora G. Anti-epidermal growth factor receptor drugs in cancer therapy. Expert Opin Invest Drugs 2002; 11: 755–68.
11 Hess G, Bunjes D, Siegert W et al. Sustained complete molecular remissions after treatment with imatinib-mesylate in patients with failure after allogeneic stem cell transplantation for chronic myelogenous leukemia: results of a prospective phase II open-label multicenter study. J Clin Oncol 2005; 23: 7583–93.
12 Hahn EA, Glendenning GA, Sorensen MV et al. Quality of life in patients with newly diagnosed chronic phase chronic myeloid leukemia on imatinib versus interferon alfa plus low-dose cytarabine: results from the IRIS Study. J Clin Oncol 2003; 21: 2138–46.
13 O’Brien SG, Guilhot F, Larson RA et al. Imatinib com-pared with interferon and low-dose cytarabine for newly diagnosed chronic-phase chronic myeloid leukemia. N Engl J Med 2003; 348: 994–1004.
14 Jorissen RN, Walker F, Pouliot N, Garrett TP, Ward CW, Burgess AW. Epidermal growth factor receptor: mecha-nisms of activation and signalling. Exp Cell Res 2003; 284: 31–53.
15 Pao W, Miller VA. Epidermal growth factor receptor muta-tions, small-molecule kinase inhibitors, and non-small-cell lung cancer: current knowledge and future directions. J Clin Oncol 2005; 23: 2556–68.
16 Barker AJ, Gibson KH, Grundy W et al. Studies leading to the identification of ZD1839 (IRESSA): an orally active, selective epidermal growth factor receptor tyrosine kinase inhibitor targeted to the treatment of cancer. Bioorg Med Chem Lett 2001; 11: 1911–14.
17 Wakeling AE, Guy SP, Woodburn JR et al. ZD1839 (Iressa): an orally active inhibitor of epidermal growth factor signaling with potential for cancer therapy. Cancer Res 2002; 62: 5749–54.
18 Sirotnak FM. Studies with ZD1839 in preclinical models. Semin Oncol 2003; 30: 12–20.
19 Sirotnak FM, Zakowski MF, Miller VA, Scher HI, Kris MG. Efficacy of cytotoxic agents against human tumor xenografts is markedly enhanced by coadministration of ZD1839 (Iressa), an inhibitor of EGFR tyrosine kinase. Clin Cancer Res 2000; 6: 4885–92.
20 She Y, Lee F, Chen J et al. The epidermal growth factor receptor tyrosine kinase inhibitor ZD1839 selectively potentiates radiation response of human tumors in nude mice, with a marked improvement in therapeutic index. Clin Cancer Res 2003; 9: 3773–8.
21 Baselga J, Rischin D, Ranson M et al. Phase I safety, pharmacokinetic, and pharmacodynamic trial of ZD1839, a selective oral epidermal growth factor receptor tyrosine
kinase inhibitor, in patients with five selected solid tumor types. J Clin Oncol 2002; 20: 4292–302.
22 Herbst RS, Maddox AM, Rothenberg ML et al. Selective oral epidermal growth factor receptor tyrosine kinase inhibitor ZD1839 is generally well-tolerated and has activity in non-small-cell lung cancer and other solid tumors: results of a phase I trial. J Clin Oncol 2002; 20: 3815–25.
23 Ranson M, Hammond LA, Ferry D et al. ZD1839, a selective oral epidermal growth factor receptor-tyrosine kinase inhibitor, is well tolerated and active in patients with solid, malignant tumors: results of a phase I trial. J Clin Oncol 2002; 20: 2240–50.
24 Fukuoka M, Yano S, Giaccone G et al. Multi-institutional randomized phase II trial of gefitinib for previously treated patients with advanced non-small-cell lung cancer (The IDEAL 1 Trial) [corrected]. J Clin Oncol 2003; 21: 2237– 46.
25 Kris MG, Natale RB, Herbst RS et al. Efficacy of gefitinib, an inhibitor of the epidermal growth factor receptor tyrosine kinase, in symptomatic patients with non-small cell lung cancer: a randomized trial. JAMA 2003; 290: 2149–58.
26 Herbst RS. Dose-comparative monotherapy trials of ZD1839 in previously treated non-small cell lung cancer patients. Semin Oncol 2003; 30: 30–8.
27 Ciardiello F, Caputo R, Bianco R et al. Antitumor effect and potentiation of cytotoxic drugs activity in human can-cer cells by ZD-1839 (Iressa), an epidermal growth factor receptor-selective tyrosine kinase inhibitor. Clin Cancer Res 2000; 6: 2053–63.
28 Giaccone G, Herbst RS, Manegold C et al. Gefitinib in combination with gemcitabine and cisplatin in advanced non-small-cell lung cancer: a phase III trial – INTACT 1. J Clin Oncol 2004; 22: 777–84.
29 Herbst RS, Giaccone G, Schiller JH et al. Gefitinib in combination with paclitaxel and carboplatin in advanced non-small-cell lung cancer: a phase III trial – INTACT 2. J Clin Oncol 2004; 22: 785–94.
30 Inoue A, Saijo Y, Maemondo M et al. Severe acute inter-stitial pneumonia and gefitinib. Lancet 2003; 361: 137–9. 31 Thatcher N, Chang A, Parikh P et al. Gefitinib plus best supportive care in previously treated patients with refrac-tory advanced non-small-cell lung cancer: results from a randomised, placebo-controlled, multicentre study (Iressa Survival Evaluation in Lung Cancer). Lancet 2005; 366: 1527–37.
32 Chinnaiyan P, Huang S, Vallabhaneni G et al. Mechanisms of enhanced radiation response following epidermal growth factor receptor signaling inhibition by erlotinib (Tarceva). Cancer Res 2005; 65: 3328–35.
33 Higgins B, Kolinsky K, Smith M et al. Antitumor activity of erlotinib (OSI-774, Tarceva) alone or in combination in human non-small cell lung cancer tumor xenograft models. Anticancer Drugs 2004; 15: 503–12.
34 Perez-Soler R, Chachoua A, Hammond LA et al. Determi-nants of tumor response and survival with erlotinib in patients with non – small-cell lung cancer. J Clin Oncol 2004; 22: 3238–47.
35 Kris MG, Sandler A, Miller V et al. Cigarette smoking history predicts sensitivity to erlotinib: Results of a phase II trial in patients with bronchioloalveolar carcinoma (BAC). J Clin Oncol 2004; 22: S631 (Abstract 7062). 36 Herbst RS, Prager D, Hermann R et al. TRIBUTE. a phase
III trial of erlotinib hydrochloride (OSI-774) combined with carboplatin and paclitaxel chemotherapy in advanced non-small-cell lung cancer. J Clin Oncol 2005; 23: 5892–9. 37 Gatzemeier U, Pluzanska A, Szczesna A et al. Results of a phase III trial of erlotinib (OSI-774) combined with cispl-atin and gemcitabine (GC) chemotherapy in advanced non-small cell lung cancer (NSCLC). J Clin Oncol 2004; 22: S619 (Abstract 7010).
38 Eberhard DA, Johnson BE, Amler LC et al. Mutations in the epidermal growth factor receptor and in KRAS are predictive and prognostic indicators in patients with non-small-cell lung cancer treated with chemotherapy alone and in combination with erlotinib. J Clin Oncol 2005; 23: 5900–9.
39 Shepherd FA, Rodrigues Pereira J, Ciuleanu T et al. Erlo-tinib in previously treated non-small-cell lung cancer. N Engl J Med 2005; 353: 123–32.
40 Tracy S, Mukohara T, Hansen M, Meyerson M, Johnson BE, Janne PA. Gefitinib induces apoptosis in the EGFRL858R non-small-cell lung cancer cell line H3255. Cancer Res 2004; 64: 7241–4.
41 Gumerlock PH, Pryde BJ, Kimura T et al. Enhanced cyto-toxicity of docetaxel OSI-774 combination in non-small cell lung carcinoma (NSCLC). Proc Am Soc Clin Oncol 2003; 22: 662 (Abstract 2661).
42 Solit DB, She Y, Lobo J et al. Pulsatile administration of the epidermal growth factor receptor inhibitor gefitinib is significantly more effective than continuous dosing for sen-sitizing tumors to paclitaxel. Clin Cancer Res 2005; 11: 1983–9.
43 Carter TA, Wodicka LM, Shah NP et al. Inhibition of drug-resistant mutants of ABL, KIT, and EGF receptor kinases. Proc Natl Acad Sci U S A 2005; 102: 11011–16. 44 Burris HA, 3rd, Hurwitz HI, Dees EC et al. Phase I safety,
pharmacokinetics, and clinical activity study of lapatinib (GW572016), a reversible dual inhibitor of epidermal growth factor receptor tyrosine kinases, in heavily pre-treated patients with metastatic carcinomas. J Clin Oncol 2005; 23: 5305–13.
45 Albanell J, Gascon P. Small molecules with EGFR-TK inhibitor activity. Curr Drug Targets 2005; 6: 259–74. 46 Kwak EL, Sordella R, Bell DW et al. Irreversible inhibitors
of the EGF receptor may circumvent acquired resistance to gefitinib. Proc Natl Acad Sci USA 2005; 102: 7665–70. 47 Lynch TJ, Bell DW, Sordella R et al. Activating mutations
respon-siveness of non-small-cell lung cancer to gefitinib. N Engl J Med 2004; 350: 2129–39.
48 Paez JG, Janne PA, Lee JC et al. EGFR mutations in lung cancer: correlation with clinical response to gefitinib ther-apy. Science 2004; 304: 1497–500.
49 Kosaka T, Yatabe Y, Endoh H, Kuwano H, Takahashi T, Mitsudomi T. Mutations of the epidermal growth factor receptor gene in lung cancer: biological and clinical impli-cations. Cancer Res 2004; 64: 8919–23.
50 Huang SF, Liu HP, Li LH et al. High frequency of epider-mal growth factor receptor mutations with complex pat-terns in non-small cell lung cancers related to gefitinib responsiveness in Taiwan. Clin Cancer Res 2004; 10: 8195–203.
51 Marchetti A, Martella C, Felicioni L et al. EGFR muta-tions in non-small-cell lung cancer: analysis of a large series of cases and development of a rapid and sensitive method for diagnostic screening with potential implica-tions on pharmacologic treatment. J Clin Oncol 2005; 23: 857–65.
52 Han SW, Kim TY, Hwang PG et al. Predictive and prog-nostic impact of epidermal growth factor receptor muta-tion in non-small-cell lung cancer patients treated with gefitinib. J Clin Oncol 2005; 23: 2493–501.
53 Chou TY, Chiu CH, Li LH et al. Mutation in the tyrosine kinase domain of epidermal growth factor receptor is a predictive and prognostic factor for gefitinib treatment in patients with non-small cell lung cancer. Clin Cancer Res 2005; 11: 3750–7.
54 Mitsudomi T, Kosaka T, Endoh H et al. Mutations of the epidermal growth factor receptor gene predict prolonged survival after gefitinib treatment in patients with non-small-cell lung cancer with postoperative recurrence. J Clin Oncol 2005; 23: 2513–20.
55 Qin BM, Chen X, Zhu JD, Pei DQ. Identification of EGFR kinase domain mutations among lung cancer patients in China: implication for targeted cancer therapy. Cell Res 2005; 15: 212–7.
56 Shigematsu H, Lin L, Takahashi T et al. Clinical and biological features associated with epidermal growth factor receptor gene mutations in lung cancers. J Natl Cancer Inst 2005; 97: 339–46.
57 Yang SH, Mechanic LE, Yang P et al. Mutations in the tyrosine kinase domain of the epidermal growth factor receptor in non-small cell lung cancer. Clin Cancer Res 2005; 11: 2106–10.
58 Hsieh RK, Lim KH, Kuo HT, Tzen CY, Huang MJ. Female sex and bronchioloalveolar pathologic subtype predict EGFR mutations in non-small cell lung cancer. Chest 2005; 128: 317–21.
59 Sordella R, Bell DW, Haber DA, Settleman J. Gefitinib-sensitizing EGFR mutations in lung cancer activate anti-apoptotic pathways. Science 2004; 305: 1163–7. 60 Kim CF, Jackson EL, Woolfenden AE et al. Identification
of bronchioalveolar stem cells in normal lung and lung cancer. Cell 2005; 121: 823–35.
61 Zell JA, Ou SH, Ziogas A, Anton-Culver H. Epidemiology of bronchioloalveolar carcinoma: improvement in survival after release of the 1999 WHO classification of lung tumors. J Clin Oncol 2005; 23: 8396–405.
62 Paik S, Shak S, Tang G et al. A multigene assay to predict recurrence of tamoxifen-treated, node-negative breast can-cer. N Engl J Med 2004; 351: 2817–26.
63 Johnson BE, Janne PA. Selecting patients for epidermal growth factor receptor inhibitor treatment: a FISH story or a tale of mutations? J Clin Oncol 2005; 23: 6813–6. 64 Huang MJ, Lim KH, Tzen CY, Hsu HS, Yen Y, Huang BS.
EGFR mutations in malignant pleural effusion of non-small cell lung cancer: a case report. Lung Cancer 2005; 49: 413–15.
65 Sasaki H, Endo K, Konishi A et al. EGFR Mutation status in Japanese lung cancer patients: genotyping analysis using LightCycler. Clin Cancer Res 2005; 11: 2924–9.
66 Pan Q, Pao W, Ladanyi M. Rapid polymerase chain reac-tion-based detection of epidermal growth factor receptor gene mutations in lung adenocarcinomas. J Mol Diagn 2005; 7: 396–403.
67 Hochhaus A, Kreil S, Corbin AS et al. Molecular and chromosomal mechanisms of resistance to imatinib (STI571) therapy. Leukemia 2002; 16: 2190–6.
68 Kobayashi S, Boggon TJ, Dayaram T et al. EGFR mutation and resistance of non-small-cell lung cancer to gefitinib. N Engl J Med 2005; 352: 786–92.
69 Pao W, Miller VA, Politi KA et al. Acquired resistance of lung adenocarcinomas to gefitinib or erlotinib is associated with a second mutation in the EGFR kinase domain. PLoS Med 2005; 2: e73.
70 Jain A, Tindell CA, Laux I et al. Epithelial membrane protein-1 is a biomarker of gefitinib resistance. Proc Natl Acad Sci USA 2005; 102: 11858–63.
71 Pao W, Wang TY, Riely GJ et al. KRAS mutations and primary resistance of lung adenocarcinomas to gefitinib or erlotinib. PLoS Med 2005; 2: e17.
72 Kobayashi S, Ji H, Yuza Y et al. An alternative inhibitor overcomes resistance caused by a mutation of the epider-mal growth factor receptor. Cancer Res 2005; 65: 7096– 101.
73 Wu Y, Lin J, Wang K et al. EGFR mutations in lung cancers and sensitivity to gefitinib in Chinese. J Clin Oncol 2005; 23: S642 (Abstract 7089).
