Abstract
Background/Aim: MET exon 14 skipping occurs in 3-4% of patients with lung adenocarcinomas. In this study, we performed a comprehensive analysis of clinical data from Korean non-small cell lung cancer (NSCLC) patients with MET exon 14 skipping. Patients and Methods: Overall, 1,020 patients diagnosed with NSCLC between January 2015 and July 2017 were analyzed by next-generation sequencing. Results: MET exon 14 skipping was identified in 20 NSCLC patients (1.9%). The median age was 69 years (range=39-86 years), 60.0% were male, and most (55.0%) were ever-smokers. For first-line chemotherapy, the median overall survival was 9.5 months and progression-free survival was 4.0 months, respectively. Twelve patients received pemetrexed-based chemotherapy and the overall response rate was 33.3% (4/12). Among four crizotinib-treated patients, one continued therapy for 8 months with the best response being disease stability. Conclusion: Given the poor clinical outcome and response to therapy for NSCLC, and the availability of promising anti-tumor MET inhibitors, screening for the MET exon 14 skip mutation should be incorporated into clinical practice.
Lung cancer, including non-small cell lung cancer (NSCLC), is reported to be the leading cause of death from cancer in Korea (1). NSCLC accounts for approximately 85% of all cases of lung cancer (2). The identification of genetic abnormalities has dramatically changed the treatment landscape of NSCLC. Mutations in the epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK) rearrangements are the most clinically relevant targets. EGFR tyrosine kinase (TK) inhibitors have been shown to be effective in patients with specific tumor cell mutations in the EGFR TK domain (3). In addition, the newly developed ALK inhibitors –ceritinib, alectinib, and brigatinib– have been approved for ALK-positive NSCLC (4). With advances in technology, more oncogenic drivers, such as ROS1, RET, BRAF, NTRK, MET, NRG1, and others, can be identified using next generation sequencing (NGS) (5).
The MET proto-oncogene, located on chromosome 7q21-q31, encodes the tyrosine kinase receptor for hepatocyte growth factor (HGF) (6). MET is activated when the HGF ligand binds to the MET receptor leading to homodimerization and phosphorylation of intracellular tyrosine residues (7). Dysregulation of the MET pathway in lung cancer arises due to gene mutation, amplification, and rearrangement, and protein overexpression (5, 8). Among them, MET exon 14 skipping gives rise to one of the most important oncogenic drivers. MET exon 14 encodes part of the juxtamembrane domain, containing the c-Cbl E3 ubiquitin ligase binding site, Y1003 (9). Because ubiquitination tags MET receptor for degradation, MET exon 14 skipping, which produces a truncated MET receptor lacking the ubiquitin binding site, results in decreased ubiquitination and sustained MET activation (10). MET exon 14 skipping occurs in 3-4% (11) of patients with lung adenocarcinomas and is recognized as a poor prognostic factor in patients with NSCLC; it has also been associated with a poor response to standard therapies (12). In this paper, we report a comprehensive analysis of clinical data from NSCLC patients harboring MET exon 14 skipping mutation in Korea.
Flow-chart of patient selection. Samples were analyzed using Oncomine™ Focus Assay (n=441) or CancerSCAN™ (n=579).
Patients and Methods
Ethical statement. This study was approved by the institutional review board of the Samsung Medical Center (2019-07-194-002) and informed consent was waived.
Patients. A total of 1,020 patients who had been diagnosed with NSCLC were reviewed between January 2015 and July 2017 at the Samsung Medical Center. Clinical data, including patient characteristics, Eastern Cooperative Oncology Group (ECOG) performance status, surgery type, EGFR or ALK mutation, PDL1 expression and sites of metastasis, and response to chemotherapy or MET inhibitor, were retrospectively analyzed. Radiographic assessment of the response to chemotherapy or treatment with MET inhibitors was performed by a single physician (J.Y.H.) using RECIST 1.1 criteria (13).
Identification of MET exon 14 skipping. MET Exon 14 skipping was identified by NGS. Briefly, DNA and RNA were extracted from formalin-fixed paraffin-embedded or fresh biopsy tissue samples. Specimens with tumor tissues (>10% tumor content) were included in the study. In Figure 1, samples were analyzed using Oncomine™ Focus Assay (Thermo Fisher Scientific, San Francisco, CA, USA) (n=441) (14) or CancerSCAN™, a targeted sequencing platform established at the Samsung Medical Center Genomic Institute (n=579) (15). MET amplification was defined as a copy number greater than two.
Baseline characteristics of patients with NSCLC.
MET immunohistochemistry (IHC). The BenchMark XT automated slide processing system (Ventana Medical Systems, Tucson, AZ, USA) was employed. The anti-MET (SP44) (Ventana Medical Systems, Tucson, AZ, USA) antibody was used for MET IHC staining. IHC data were categorized according to the following staining scores: 0, negative; 1, weak; 2, moderate; and 3, strong (16).
Genomic landscape of all patients with MET exon 14 skipping NSCLC. Concurring alterations, including PIK3CA mutation (4 patients), TP53 mutation (2 patients), KRAS amplification (2 patients), PTEN mutation (1 patient), and KRAS mutation (1 patient) were infrequently observed with MET exon 14 skipping NSCLC. Notably, patients with MET exon 14 skipping did not harbor concurrent EGFR, BRAF, ALK, ROS1 mutations, or RET translocations, suggesting that they are mutually exclusive.
Statistical analysis. Progression-free survival (PFS) was defined as the time from the date of first-line chemotherapy to the progression of cancer or death from any cause. Overall survival (OS) was defined as the period between the date of first-line chemotherapy and death from any cause. Survival curves were estimated by the Kaplan-Meier plot. All statistical analyses were performed using R software (version 3.2.3, R for Statistics Computing, Vienna, Austria).
Results
MET exon 14 skipping was identified in 20 NSCLC patients (1.9%). The median age was 69 years (range=39-86 years), and 60.0% of the patients were male. Most patients (55.0%) were ever-smokers. Adenocarcinoma was predominant (85.0%), and we identified two cases (10.0%) with squamous cell carcinoma and one case with pleomorphic carcinoma. Among 20 patients, 15 (75.0%) had stage IV NSCLC at initial work-up. The most common metastatic site was bone (40%), followed by the pleura (35%) and brain (15%). One of the five pleomorphic carcinoma (20%) cases harbored MET exon 14 skipping. Four patients underwent lobectomy and one patient pneumonectomy. Most patients (95.0%) had ECOG performance status (PS) 0 to 2. Four of the patients tested for programmed death ligand-1 (PD-L1) expression were positive. All patients were negative for EGFR mutation and ALK rearrangements as assayed by IHC (Table I).
The genomic landscape of the patients with MET exon 14 skipping NSCLC is shown in Figure 2. Notably, patients with MET exon 14 skipping did not harbor concurrent EGFR, BRAF, ALK, ROS1 mutations, or RET translocations, suggesting that they are mutually exclusive. In contrast, concurring alterations, including PIK3CA mutation (4 patients), TP53 mutation (2 patients), SMAD4 mutation (2 patients), KRAS amplification (2 patients), PTEN mutation (1 patient), and KRAS mutation (1 patient) were infrequently observed with MET exon 14 skipping NSCLC. The MET IHC test was conducted in two patients. Of the two patients, one patient was positive (membranous, 2+), and the other negative. No patient was tested using fluorescence in situ hybridization (FISH) to detect the MET amplification.
Kaplan-Meier plots of progression-free survival and overall survival for all patients. For first line chemotherapy, the median progression-free survival (PFS) was 4.0 months [95% confidence interval (CI)=2.8-14.1] (A) and the median overall survival (OS) was 9.5 months (95%CI=6.5-23.1) (B).
For first line chemotherapy, the median PFS was 4.0 months [95% confidence interval (CI)=2.8-14.1] (Figure 3A) and the median OS was 9.5 months (95%CI=6.5-23.1) (Figure 3B). In 12 patients treated with pemetrexed-based chemotherapy, the overall response rate was 33.3% (4/12). No patient had previous exposure to MET therapy as first-line chemotherapy.
Of the 20 patients with identified MET exon 14 alterations, four patients received orally crizotinib at a starting dose of 250 mg, twice daily. Clinical and pathologic characteristics are summarized in Table II. A 69-year-old woman, never smoker who had been diagnosed with stage IV lung adenocarcinoma with brain metastasis, showed progression despite crizotinib as third-line chemotherapy (PFS, 9 days). A 62-year-old man with lung squamous cell carcinoma died 8 days after crizotinib was prescribed as fourth-line chemotherapy. A 39-year-old man with pleomorphic carcinoma died 4 days after crizotinib treatment as second-line chemotherapy. A 61-year-old man presented with a thoracic spine compression fracture along with adenocarcinoma in the right upper lung; NGS revealed the MET exon 14 skipping mutation without other genomic alterations. The patient was treated with pemetrexed and carboplatin as first-line chemotherapy. After 14 months of first-line chemotherapy, 250 mg crizotinib twice daily was initiated because of cancer progression. CT scans obtained after 8 weeks of crizotinib treatment revealed a decreased subpleural metastatic lesion in the left lower lobe and unchanged NSCLC in the right upper lobe (Figure 4). The patient continued therapy for 8 months with stable disease as the best response.
Computed tomography (CT) scans of a patient with MET exon 14 skipping showing the response while the patient was receiving crizotinib. CT scans obtained after 8 weeks of crizotinib treatment revealed a decreased subpleural metastatic lesion in the left lower lobe and unchanged tumor in the right upper lobe.
Clinical information and treatment outcomes of four patients who received crizotinib.
Discussion
In this study, we found that the incidence of MET exon 14 skipping in NSCLC was 1.9%, which is lower than that (3%) in previous studies (17). The overall incidence of MET mutations varies, occurring in 3% of squamous cell lung cancer and 3-8% of lung adenocarcinoma cases (18, 19). One study identified MET exon 14 mutations in 28 of 933 nonsquamous NSCLCs (3.0%) (20). In another study of Korean patients, MET exon 14 skipping was detected in adenocarcinoma (4.8%; 11/230) and sarcomatoid carcinoma (9.5%; 2/21) cases by histology only (21). Liu et al. have reported that pulmonary sarcomatoid carcinoma is associated with a high incidence (approximately 22%) of MET exon 14 skipping (22). The lower incidence of MET exon 14 skipping in our study might be partly attributed to the small number of patients with pleomorphic carcinoma (5/1,020) enrolled.
MET exon 14 skipping occurred more frequently in older patients and ever-smokers. These findings are consistent with those of previous studies (16). Moreover, these are quite distinct clinical features compared to that of other patients with oncogenic drivers. Regarding the initial treatment, patients treated with platinum-based chemotherapy had short PFS (median PFS=4 months) and poor outcome (median OS=9.5 months). In a previous study, an 85-year-old man received four cycles of pemetrexed and carboplatin as the first-line chemotherapy for MET exon 14 skipping NSCLC, followed by one cycle of pemetrexed with maintenance chemotherapy, but the number of lung nodules were found to have increased (23).
Currently, a variety of MET tyrosine kinase inhibitors are being assessed in clinical trials. Crizotinib has been investigated in patients with MET exon 14 skipping NSCLC and showed a 32% response rate (8/18) and a 9.1 month response duration, leading to its designation as breakthrough therapy by the Food and Drug Administration, USA (24). In our study, three of the four patients who were treated with crizotinib showed progression, and only one patient showed a durable response for more than 8 months. The lower response may be due to the enrollment of heavily pre-treated patients.
Capmatinib, an oral ATP-competitive, reversible, highly selective inhibitor of MET receptor tyrosine kinase, showed a 39.1% response rate among pretreated and 72% among treatment naive patients. Of note, a patient with brain metastasis experienced brain tumor shrinkage, suggesting that the drug penetrated in the CNS (25). Tepotinib, another highly selective MET inhibitor, demonstrated a 59.1% response rate with a 14.3-month response duration, and this drug has also been shown to have anti-brain tumor activity (26). Given their high selectivity, in contrast to previous drugs, most of these agents are quite effective.
Similar to other targeted agents, the development of acquired resistance is inevitable, and the exact mechanisms underlying this resistance have not yet been fully established. Resistance mechanisms include a secondary mutation in the tyrosine kinase domain, such as D1228N (27) or Y1230C (28), or activation of a bypass pathway, e.g., K-ras or EGFR amplification (29, 30). Further studies to determine the resistance to MET inhibitors are required.
There are several limitations to this study; it is a single cancer center study and involved a small sample size and retrospective data collection, which may have led to selection bias. Finally, most of the patients were not treated with other MET inhibitors, such as capmatinib, merestinib, or tepotinib.
In conclusion, MET exon 14 skipping was detected in 1.9% of Korean patients with NSCLC by NGS. MET exon 14 skipping occurred more frequently in older patients and ever-smokers. The median overall survival was limited to within 12 months. Given the poor clinical outcome and response to standard treatments for advanced non-small cell lung cancer, and the availability of MET inhibitors with promising anti-tumor activities, screening for the MET exon 14 skipping mutation should be incorporated into clinical practice.
Acknowledgements
This research was supported by the Collaborative Genome Program for Fostering New Post-Genome Industry of the National Research Foundation (NRF) funded by the Ministry of Science and ICT (MSIT) (No. NRF-2017M3C9A6044633).
Footnotes
Authors' Contributions
Study design: HAJ, JMS, SHL, JSA; Study supervision: KP, MJA;Data collection: JYH, BMK; Data analysis: BMK, JHS; Statistical analysis: JYH; Manuscript preparation: JYH, MJA; Manuscript approval: all Authors.
This article is freely accessible online.
Conflicts of Interest
The Authors have no conflicts of interest to declare regarding this study.
- Received January 22, 2020.
- Revision received February 4, 2020.
- Accepted February 7, 2020.
- Copyright© 2020, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved
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