Dietmaier W, Wallinger S, Bocker T, Kullmann F, Fishel R, Rüschoff J
Institute of Pathology, University of Regensburg, Germany.
Cancer Res. 1997 Nov 1;57(21):4749-56.
Alterations of the length of simple repetitive genomic sequences (microsatellite instability, MSI) characterize a distinct mechanism of colorectal carcinogenesis. Such MSI has been found to be associated with hereditary nonpolyposis colorectal cancer (HNPCC) that involves mutation of the human mismatch repair genes hMSH2 and hMLH1 as well as many sporadic cancers of most tissue types. Although the study of MSI status is a useful tool for HNPCC screening and for the determination of tumor prognosis in sporadic cases of colorectal cancer, the reliability of MSI diagnosis is still a subject of debate. Here we have examined 58 primary colorectal tumors (selected from a cohort of 200) using 31 microsatellite markers that comprised the most frequent simple repeat types. The expression of the hMSH2 and hMLH1 mismatch repair proteins was studied by immunohistochemistry, and most patients were surveyed for at least 2 years. Reproducibility of gel interpretation, as well as diagnostic sensitivity and specificity of the MSI status, were determined. We found that unambiguous determination of band shifts as well as MSI diagnosis were closely related to the type of the marker repeat and that MSI could be subdivided into "high" MSI (>20% unstable loci), "low" MSI (<10% unstable loci), and microsatellite stable (0% unstable loci). One-half of the patients with high MSI tumors (n = 8) fulfilled either the Amsterdam criteria (n = 4), had at least one relative with HNPCC-related carcinoma (n = 2), or were diagnosed with colorectal cancer at an age below 45 years (n = 2). Fourteen of the 15 high MSI tumors had lost either hMSH2 (n = 8) or hMLH1 (n = 6) protein expression. In contrast, all of the low MSI tumors and the MSI-negative tumors displayed normal expression of hMSH2 and hMLH1. These studies provide a clear recommendation for the uniform use of a panel of 10 microsatellites and a definition of at least 40% instability (using these defined marker loci) in the diagnostic analysis of MSI.
简单重复基因组序列长度的改变（微卫星不稳定性，MSI）是结直肠癌发生的一种独特机制。已发现这种MSI与遗传性非息肉病性结直肠癌（HNPCC）相关，HNPCC涉及人类错配修复基因hMSH2和hMLH1的突变以及大多数组织类型的许多散发性癌症。尽管MSI状态的研究是HNPCC筛查以及散发性结直肠癌病例肿瘤预后判定的有用工具，但MSI诊断的可靠性仍是一个有争议的话题。在此，我们使用包含最常见简单重复类型的31个微卫星标记物检测了58例原发性结直肠癌肿瘤（从200例队列中选取）。通过免疫组织化学研究hMSH2和hMLH1错配修复蛋白的表达，并且对大多数患者进行了至少2年的随访。确定了凝胶解读的可重复性以及MSI状态的诊断敏感性和特异性。我们发现条带移位的明确判定以及MSI诊断与标记物重复类型密切相关，并且MSI可细分为“高”MSI（>20%不稳定位点）、“低”MSI（<10%不稳定位点）和微卫星稳定（0%不稳定位点）。高MSI肿瘤患者中有一半（n = 8）符合阿姆斯特丹标准（n = 4），有至少一位患有与HNPCC相关癌症的亲属（n = 2），或者在45岁以下被诊断为结直肠癌（n = 2）。15例高MSI肿瘤中有14例失去了hMSH2（n = 8）或hMLH1（n = 6）蛋白表达。相反，所有低MSI肿瘤和MSI阴性肿瘤均显示hMSH2和hMLH1正常表达。这些研究为在MSI诊断分析中统一使用10个微卫星标记物面板以及定义至少40%的不稳定性（使用这些定义的标记位点）提供了明确建议。
