Background: Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gastrointestinal tract. The majority of GISTs have a gain-of-function mutation of the c-kit or PDGFRA gene in the interstitial cells of Cajal. Although surgery is the most effective treatment for resectable primary GISTs, postoperative recurrence or metastasis has been observed after surgical resection in 40-90% of patients without adjuvant therapy. Metastatic GISTs are found most commonly in the liver, which are difficult to cure with surgical treatment alone. Although tyrosine kinase inhibitor (TKI) imatinib mesylate (Gleevec) is thought to be the most effective agent for treating GISTs, secondary resistance often arises during therapy due to secondary mutations. In this era of TKIs, control of liver metastasis remains to be an important issue in the treatment of GISTs and mechanisms of liver metastasis need to be elucidated. In this study, we compared gene expression and micro RNA (miRNA) expression profiles between gastric GISTs and metastatic liver GISTs to address mechanisms of GIST liver metastasis and to detect novel molecular markers for prediction of the postoperative prognosis of GIST patients.

Methods: Frozen tissue specimens of three gastric GISTs and four metastatic liver GISTs were utilized for cDNA microarray analysis. None of the patients had received imatinib therapy before surgery. Formalin-fixed paraffin-embedded (FFPE) tissues of 104 primary GISTs and 13 metastatic GISTs from 107 patients who had undergone surgery were included for immunohistochemistry investigations. GIST cells were isolated from FFPE tissues of five gastric GISTs at low risk, five gastric GISTs at high risk and six metastatic liver GISTs surgically resected, and miRNA expression was analyzed using TaqMan miRNA array.

Results: Expression levels were higher for 165 genes and lower for 146 genes in metastatic liver GIST. The upregulation of five oncogenes including versican and downregulation of four tumor suppressor genes, Cadherin8, Protocadherin10, NRCAM and CD9 were confirmed by qRT-PCR. Immunohistochemistry in 117 GISTs revealed that protein levels of versican and CD9 were higher and lower, respectively, in metastatic GIST. High expression of versican and low expression of CD9 in 104 primary gastric GISTs correlated with poor disease-free survival (P= 0.0078 and P= 0.0018). In miRNA array analysis, miR-122 was the most highly expressed in liver metastasis compared with primary gastric GISTs, consistent with our earlier papers that showed the overexpression of miR-122 and concomitant suppression of CAT1 in colorectal liver metastasis (Cancer Sci 104,624-30,2013).

Conclusions: In addition to the c-kit gene mutation, genetic or epigenetic changes other than c-kit and alteration of miRNA expression such as miR-122 play important roles in the metastatic process of gastric GIST.

Citation Format: Hirotoshi Kikuchi, Ichirota Iino, Shinichiro Miyazaki, Yusuke Ozaki, Yoshihiro Hiramatsu, Manabu Ohta, Kinji Kamiya, Takanori Sakaguchi, Satoshi Baba, Haruhiko Sugimura, Mitsutoshi Setou, Hiroyuki Konno. cDNA and miRNA microarray analysis comparing gastric and metastatic liver gastrointestinal stromal tumors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4008. doi:10.1158/1538-7445.AM2014-4008