Mutations in the tyrosine kinase domain of the EGFR gene associated with gefitinib response in non-small-cell lung cancer
Introduction
Epidermal growth factor receptor (EGFR) is surfacing as an important target for therapy. EGFR stimulates cell growth and differentiation after binding of specific ligands, acting as a membrane-bound receptor with intrinsic tyrosine kinase (TK) activity in the intracellular domain. Overexpression of EGFR has been shown to transform NIH 3T3 cells in an EGF-dependent manner [1]. Dimerization with other erbB receptors and the activation of the kinase domain are essential for phosphorylation of a variety of intracellular protein cascades. EGFR is amplified in 9% of NSCLC cases. Therefore, it is broadly accepted that overexpression of EGFR in NSCLC is commonly regulated on the transcriptional level [1]. The Iressa Dose Evaluation in Advanced Lung Cancer (IDEAL) 1 trial investigated the efficacy of oral gefitinib in advanced NSCLC patients who had previously received one or two chemotherapy regimens. The response rate was higher for Japanese than for non-Japanese patients (27.5% versus 10.4%; odds ratio = 3.27; P = 0.0023). The response rate was also 2.5 times higher in women than in men and 3.5 times higher in adenocarcinoma than in other histologies [2]. The IDEAL 2 study was carried out only in patients in the United States previously treated with two or more regimens containing cisplatin or carboplatin plus docetaxel. The overall response rate was 10%, with a median survival of 6 months and one-year survival of 25%. Response rate was 19% for women and 3% for men, 13% for adenocarcinoma and 4% for other histologies [3]. In addition to the IDEAL 1 and IDEAL 2 trials, 122 patients were treated on the Expanded Access Program, a compassionate use program, at the Memorial Sloan-Kettering Cancer Center. Results confirmed the better response in women (19%) than in men (8%) (P = 0.14) and in adenocarcinoma (19%) than in other histologies (0%) (P = 0.004). Response was also higher in never-smokers (36%) than in former or current smokers (8%) (P = 0.001) [4].
The Iressa NSCLC Trial Assessing Combination Treatment (INTACT) 1 investigated the efficacy of gefitinib versus placebo in combination with cisplatin plus gemcitabine in chemotherapy-naïve patients from Europe (74%), North America (12.7%), Asia (5.3%), South America (4.1%) and South Africa (1.6%). No differences were observed in response, time to progression or median survival [5]. In the INTACT 2 trial, where 80% of the patients were from the United States, patients were randomized to receive paclitaxel plus carboplatin with or without gefitinib. There was no survival advantage in any of the subgroups when gefitinib was added to chemotherapy, but there was a trend toward improved survival in the subgroup of patients with adenocarcinoma who had received chemotherapy for more than 90 days [6].
Personalized treatment can be based on the kinases that are mutationally altered in individual tumors. TKs are central regulators of signaling pathways that control differentiation, transcription, cell cycle progression, apoptosis, motility and invasion. TK mutations have been described in PI3KCA, which encodes the p110α catalytic subunit of phosphatidylinositol 3-kinase (PI3K) [7], [8]. Mutations have also been described in B-raf, the most common of which is a substitution mutation changing valine 599 to glutamic acid (V599E), which dramatically enhances B-raf activity [9]. Recently, EGFR TK mutations have been described and linked to gefitinib sensitivity in NSCLC patients [10], [11]. Paez et al. [10] observed mutations in the EGFR TK domain only in responders. These mutations were more frequent in women (9/45, 20%) than in men (7/74, 9%) (P = 0.009), in adenocarcinoma (15/70, 21%) than in other histological subtypes (1/49, 2%) (P = 0.001), in non-smokers (13/37, 54%) than in smokers (6/62, 11%) (P = 0.0009), and in Japanese (15/58, 26%) than in non-Japanese subjects (1/61, 2%) (P = 0.001). In addition, no mutations were observed in four patients who progressed on gefitinib, while all five tumors from gefitinib responders harbored EGFR mutations (P = 0.0027). Lynch et al. [11] also identified mutations in the EGFR TK domain in eight of nine patients with gefitinib-responsive NSCLC, compared with none of the seven non-responders. In both studies, the majority of mutations was clustered in exons 18, 19 and 21 and were either in-frame deletion or heterozygous missense mutations around the adenosine triphosphate (ATP) binding pocket [12]. Substitution mutations changing leucine 858 to arginine (L858R), guanine 719 to serine (G719S), and leucine 861 to glutamine (L861Q) lay in the activation and glycine-rich P loops, which are important for autoregulation, while multiple deletion mutations clustered in the region spanning codons 746 to 750 (ELREA), around the active site of the kinase [10], [11]. Mutant EGFR has also been found in gefitinib-sensitive cell lines [10], [11].
These studies demonstrate that mutations around the EGFR TK domain enhance ligand-inducing EGFR autophosphorylation and confer increased sensitivity to gefitinib, suggesting that gefitinib may be highly effective for treating NSCLC patients with somatic EGFR mutations. We have studied EGFR TK mutations in NSCLC patients from Japan and Spain who were treated with gefitinib after second- or third-line chemotherapy and correlated results with response.
Section snippets
Patients
Paraffin-embedded tumor tissue was obtained from a total of 34 NSCLC patients who had been treated with gefitinib as part of Expanded Access programs after at least second- or third-line chemotherapy failure. Eighteen samples, including 17 resected primary tumors and one bronchial biopsy of a metastatic tumor, were from the National Kyushu Cancer Center in Fukuoka, Japan, and 16 samples, including eight resected primary tumors and eight bronchial biopsies of metastatic tumors, were from the
Results
Patient characteristics are shown in Table 1, broken down by the presence or absence of EGFR mutations. Eight of the 34 patients harbored mutations. All mutations observed were somatic and were found exclusively in adenocarcinomas and more frequently in non-smokers than in smokers. Gefitinib response was observed in 7 of 8 patients (87.5%) with EGFR mutations and in 3 of 24 (12.5%) with wild-type EGFR (P = 0.0003). Two patients with wild-type EGFR were not evaluable for response. Although
Discussion
In the present study, we have observed that EGFR mutations are a strong predictor of gefitinib response in chemoresistant NSCLC patients. Seven of eight patients (87.5%) with EGFR mutations attained an objective response, in contrast with only three of 24 patients (12.5%) with wild-type EGFR (P < 0.0003). These results mirror accumulated data from three studies [10], [11], [14], in which 25 of 31 (81%) NSCLC patients with EGFR mutations attained objective response, while none of 29 non-responders
Acknowledgements
This study was partially supported by the Spanish Ministry of Health grants provided through Red Temática de Investigación Cooperativa de Centros de Cáncer (CO-010) and Red de Centros de Epidemiología y Salud Pública (RCESP), and by funding from La Fundació Badalona Contra el Càncer.
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