Analysis of gene alterations in the premalignant lesion of colorectum

近年来分子生物学的研究进展表明，许多肿瘤相关基因在结直肠多步骤癌变过程中起着重要作用。然而，许多报道都是基于对一系列结直肠腺瘤或癌组织的分析，对于每个病例的发生时间或基因改变的确切作用知之甚少。我们在本研究中使用的腺瘤癌是结肠腺瘤-癌序列中最初始的恶性肿瘤，被认为是研究与恶性转化相关的基因改变的理想临床材料。此外，我们采用的微量分析使我们能够分析正常上皮，不同级别异型性腺瘤和每个病例中污染最小的癌的DNA。我们可以将DNA分析结果与病理结果（包括免疫组织化学）进行比较，因此可以对组织病理学进行更深入的遗传分析。我们目前的研究结果清楚地表明p53基因的改变在从腺瘤到癌的恶性转化的转折点中起着关键作用。因此，p53基因改变的分析在临床应用中也应该是有用的。相反，根据以往的报道，K-ras基因突变与腺瘤的非典型性分级有关。在腺瘤和腺瘤中，K-ras的突变率没有差异，没有证据表明K-ras参与了恶性转化。通过对不同程度异型病变的K-ras的分析，提示K-ras突变仅仅是发育不良的结果。我们还分析了结直肠肿瘤中DNA错配修复系统和细胞周期调节因子WAF1、cyclin D、cdc2/cdk2异常引起的基因组不稳定性，并获得了一些初步结果。其中一些结果已经在论文中发表，如本报告所述。少

The recent advance in molecular biology revealed that a number of cancer-associated genes play an important role in multistep carcinogenesis in colorectum. However, many of the reports are based on the analysis on a series of colorectal adenoma or carcinoma tissues, and little is known about the timing of the occurence or the precise role of the gene alteration in cach individual case. Carcinoma in adenoma which we used in the present study is the very initial malignancy in adenoma-carcinoma sequence in colon and is thought to be an ideal clinical material for the study of the gene alteration associated with malignant transformation. In addition, microanalysis which we employed enabled us to analyze DNA of both normal cpithelium, adenoma with the different grade of atypia and the carcinoma in each case with the minimal contamination. We are able to compare the result of DNA analysis to the pathological findings including immunohistochemistry, therefore, genetic analysis of histopatholo … More gical level can be done. The result of our present study clearly show that the p53 gene alteration plays a key role in the turning point of malignant conversion from adenoma to carcinoma. Therefore, analysis of p53 gene alteration should be useful also in the clinical application. On the contrary, K-ras gene mutation was shown to be associated with the grade of atypia of adenoma in accordance with the previous reports. There is no difference in the mutation rate of K-ras in between adenoma and carcinoma in adenoma, showing no evidence of the participation of K-ras in malignant transformation. The analysis of K-ras in the multple lesions with the different grade of atypia suggested that K-ras mutaion is merely the consequence of the development of dysplasia. We also did the analysis of genomic instability derived from the abnormality in DNA mismatch repair system and the cell cycle regulator such as WAF1, cyclin D,cdc2/cdk2 in colorectal tumor, and obtained some preliminary results. Some of these result have been already published in the paper as described in this report. Less