Supplementary Material for: Immunohistochemical Analysis of Mismatch Repair Gene Proteins in Early Gastric Cancer Based on Microsatellite Status

<b><i>Background:</i></b> Microsatellite instability (MSI) is a major pathway involved in gastric carcinogenesis and is observed in 10–20% of early gastric cancers (EGCs). Early detection of EGCs with an MSI-high phenotype would be useful for elucidating the mechanisms of gastric carcinogenesis and improving outcomes in patients with GC. <b><i>Objective:</i></b> We explored the usefulness of immunohistochemical expression of mismatch repair (MMR) proteins, including MLH1, PMS2, MSH2, and MSH6 in EGC. <b><i>Methods:</i></b> We examined the expression of 4 MMR proteins using immunohistochemistry in 119 patients with EGC based on MS status, as determined by polymerase chain reaction-microsatellite analysis. In addition, methylation of the <i>MLH1</i> gene was quantified by pyrosequencing. <b><i>Results:</i></b> EGCs were classified into 46 MSI-high phenotypes and 73 microsatellite stable (MSS) phenotypes. Although loss of MLH1 expression was associated with loss of PMS2 expression in the MSI-high phenotype, discordant cases of loss of expression between MLH1 and PMS2 were found (MLH1 [−]/PMS2 [+], 3 cases). Loss of MLH1/PMS2 expression was observed in 2 of 73 MSS phenotypes. Loss of MSH2/MSH6 expression was found in 4 of 46 MSI-high phenotypes, whereas loss of MSH2/MSH6 expression was not detected in the MSS phenotype. In addition, loss of MLH1 expression was correlated with methylation of <i>MLH1</i>. However, there were discordant cases in which loss of MLH1 expression was not accompanied by methylation of <i>MLH1</i>. <b><i>Conclusion:</i></b> Although immunostaining of MMR proteins could help predict MSI in EGCs, immunostaining did not have the same value as genetic testing for determination of MSI.

<b><i>背景：</i></b> 微卫星不稳定（Microsatellite instability, MSI）是参与胃癌发生的主要通路，在10%~20%的早期胃癌（early gastric cancers, EGC）中可观察到此现象。早期检测携带MSI高表型的早期胃癌，有助于阐明胃癌发生机制并改善胃癌患者的预后。
<b><i>目的：</i></b> 本研究探讨错配修复（mismatch repair, MMR）蛋白（包括MLH1、PMS2、MSH2及MSH6）在早期胃癌中的免疫组化表达价值。
<b><i>方法：</i></b> 本研究基于聚合酶链反应-微卫星分析（polymerase chain reaction-microsatellite analysis）确定的微卫星状态，采用免疫组化法检测119例早期胃癌患者的4种MMR蛋白表达情况。此外，通过焦磷酸测序（pyrosequencing）定量检测MLH1基因的甲基化水平。
<b><i>结果：</i></b> 早期胃癌被分为46例MSI高表型组与73例微卫星稳定（microsatellite stable, MSS）组。尽管在MSI高表型中，MLH1表达缺失与PMS2表达缺失具有相关性，但仍存在MLH1与PMS2表达不一致的病例（MLH1[-]/PMS2[+]，共3例）。73例微卫星稳定病例中，有2例出现MLH1/PMS2表达缺失。46例MSI高表型病例中，有4例出现MSH2/MSH6表达缺失，而微卫星稳定组未检测到MSH2/MSH6表达缺失。此外，MLH1表达缺失与MLH1基因甲基化具有相关性，但也存在MLH1表达缺失却未伴随MLH1基因甲基化的不一致病例。
<b><i>结论：</i></b> 尽管MMR蛋白免疫染色可辅助预测早期胃癌的MSI状态，但免疫组化检测在确定微卫星状态方面的价值并不等同于基因检测。