Prevalence and Clinicopathological Significance of MET Overexpression and Gene Amplification in Patients with Gallbladder Carcinoma

Abstract

Purpose: Mesenchymal epithelial transition (MET) is a proto-oncogene that encodes a heterodimeric transmembrane receptor tyrosine kinase for the hepatocyte growth factor. Aberrant MET signaling has been described in several solid tumors-especially non-small cell lung cancer- and is associated with tumor progression and adverse prognosis. As MET is a potential therapeutic target, information regarding its prevalence and clinicopathological relevance is crucial.

Materials and methods: We investigated MET expression and gene amplification in 113 gallbladder cancers using tissue microarray. Immunohistochemistry was used to evaluate MET overexpression, and silver/fluorescence in situ hybridization (ISH) was used to assess gene copy number.

Results: MET overexpression was found in 37 cases of gallbladder carcinoma (39.8%), and gene amplification was present in 17 cases (18.3%). MET protein expression did not correlate with MET amplification. MET amplification was significantly associated with aggressive clinicopathological features, including high histological grade, advanced pT category, lymph node metastasis, and advanced American Joint Committee on Cancer stage. There was no significant correlation between any clinicopathological factors and MET overexpression. No difference in survival was found with respect to MET overexpression and amplification status.

Conclusion: Our data suggested that MET might be a potential therapeutic target for targeted therapy in gallbladder cancer, because MET amplification was found in a subset of tumors associated with adverse prognostic factors. Detection of MET amplification by ISH might be a useful predictive biomarker test for anti-MET therapy.

Keywords: Gallbladder cancer; Gene amplification; Gene copy number; Immunohistochemistry; In situ hybridization; MET.

Fig. 1.

Representative sections of immunohistochemical (IHC) scores for MET expression in gallbladder cancers (×400). (A) IHC score 3, strong cytoplasmic/membranous staining in almost all tumor cells. (B) IHC score 2, more than 50% of tumor cells with moderate staining intensity but < 50% strong intensity. (C) IHC score 1, weak staining in more than 50% of tumor cells. (D) IHC score 0, no staining observed in invasive tumor cells.

Fig. 2.

Representative sections of silver in situ hybridization (SISH) and fluorescence in situ hybridization (FISH) analyses of MET/centromere 7 (CEP7) (×1,000). (A) SISH, no MET amplification, 1-2 MET gene signals (black), and 1-2 CEP7 signals (red) were present in each nucleus. (B) SISH, low-grade MET copy number gain, 2-7 MET gene signals (black), and 1-2 CEP7 (red) were present in each nucleus. (C) SISH, high-level amplification, 7-8 or more MET gene signals (black), and 1-5 CEP7 (red) were present in each nucleus. (D) FISH, high-level amplification, 5-10 or more MET gene signals (green), and 4-5 CEP7 (red) were present in each nucleus.

Fig. 3.

Representative section of silver in situ hybridization on whole section. (A) Yellow and red circle highlight the nonamplified lesion and amplified lesion, respectively. (B) The tumor cells exhibit 1-2 c-MET gene signals (black), and 1-2 centromere 7 signals (red) in each nucleus. (C) In the amplified lesion, tumor cells exhibit 4-12 c-MET gene signals (×1,000).

Fig. 4.

Kaplan-Meier survival curves of gallbladder cancer patients stratified on the basis of MET amplification status. (A) Recurrence-free survival (RFS) according to MET amplification (log-rank test, p=0.436). (B) Overall survival (OS) according to MET amplification (log-rank test, p=0.121).