Jin Hei-Ying, Liu Xiufang, Li Vicky Ka Ming, Ding Yijiang, Yang Bolin, Geng Jianxiang, Lai Rensheng, Ding Shuqing, Ni Min, Zhao Ronghua
National Center of Colorectal Surgery, 3rd Affiliated Hospital of Nanjing University of Traditional Chinese Medicine, 1 Jinling Road, Nanjing 210001, China.
BMC Cancer. 2008 Feb 7;8:44. doi: 10.1186/1471-2407-8-44.
Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant syndrome. The National Cancer Institute (NCI) has recommended the Revised Bethesda guidelines for screening HNPCC. There has been a great deal of research on the value of these tests in other countries. However, literature about the Chinese population is scarce. Our objective is to detect and study microsatellite instability (MSI) and mismatch repair (MMR) gene germline mutation carriers among a Chinese population with colorectal cancer.
In 146 prospectively recruited consecutive patients with clinically proven colorectal cancer, MSI carriers were identified by analysis of tumor tissue using multiplex fluorescence polymerase chain reaction (PCR) using the NCI recommended panel and classified into microsatellite instability-low (MSI-L), microsatellite instability-high (MSI-H) and microsatellite stable (MSS) groups. Immunohistochemical staining for MSH2, MSH6 and MLH1 on tissue microarrays (TMAs) was performed, and methylation of the MLH1 promoter was analyzed by quantitative methylation specific PCR (MSP). Germline mutation analysis of blood samples was performed for MSH2, MSH6 and MLH1 genes.
Thirty-four out of the 146 colorectal cancers (CRCs, 23.2%) were MSI, including 19 MSI-H CRCs and 15 MSI-L CRCS. Negative staining for MSH2 was found in 8 CRCs, negative staining for MSH6 was found in 6 CRCs. One MSI-H CRC was negative for both MSH6 and MSH2. Seventeen CRCs stained negatively for MLH1. MLH1 promoter methylation was determined in 34 MSI CRCs. Hypermethylation of the MLH1 promoter occurred in 14 (73.7%) out of 19 MSI-H CRCs and 5 (33.3%) out of 15 MSI-L CRCs. Among the 34 MSI carriers and one MSS CRC with MLH1 negative staining, 8 had a MMR gene germline mutation, which accounted for 23.5% of all MSI colorectal cancers and 5.5% of all the colorectal cancers. Five patients harbored MSH2 germline mutations, and three patients harbored MSH6 germline mutations. None of the patients had an MLH1 mutation. Mutations were commonly located in exon 7 and 12 of MSH2 and exon 5 of MSH6. Right colonic lesions and mucinous carcinoma were not common in MSI carriers.
Our data may imply that the characteristics of HNPCC in the Chinese population are probably different from those of Western countries. Application of NCI recommended criteria may not be effective enough to identify Chinese HNPCC families. Further studies are necessary to echo or refute our results so as to make the NCI recommendation more universally applicable.
遗传性非息肉病性结直肠癌（HNPCC）是一种常染色体显性综合征。美国国立癌症研究所（NCI）已推荐修订后的贝塞斯达指南用于HNPCC的筛查。在其他国家，针对这些检测的价值已有大量研究。然而，关于中国人群的文献却很匮乏。我们的目的是在患有结直肠癌的中国人群中检测和研究微卫星不稳定性（MSI）和错配修复（MMR）基因种系突变携带者。
在146例前瞻性招募的经临床证实患有结直肠癌的连续患者中，使用NCI推荐的检测板，通过多重荧光聚合酶链反应（PCR）分析肿瘤组织来鉴定MSI携带者，并将其分为微卫星低度不稳定（MSI-L）、微卫星高度不稳定（MSI-H）和微卫星稳定（MSS）组。对组织芯片（TMA）上的MSH2、MSH6和MLH1进行免疫组织化学染色，并通过定量甲基化特异性PCR（MSP）分析MLH1启动子的甲基化情况。对血液样本进行MSH2、MSH6和MLH1基因的种系突变分析。
146例结直肠癌（CRC）中有34例（23.2%）为MSI，其中包括19例MSI-H CRC和15例MSI-L CRC。8例CRC中发现MSH2染色阴性，6例CRC中发现MSH6染色阴性。1例MSI-H CRC的MSH6和MSH2均为阴性。17例CRC的MLH1染色阴性。在34例MSI CRC中测定了MLH1启动子甲基化情况。19例MSI-H CRC中有14例（73.7%）发生MLH1启动子高甲基化，15例MSI-L CRC中有5例（33.3%）发生MLH1启动子高甲基化。在34例MSI携带者和1例MLH1染色阴性的MSS CRC中，有8例存在MMR基因种系突变，占所有MSI结直肠癌的23.5%，占所有结直肠癌的5.5%。5例患者携带MSH2种系突变，3例患者携带MSH6种系突变。所有患者均未发生MLH1突变。突变常见于MSH2的第7和12外显子以及MSH6的第5外显子。MSI携带者中右半结肠病变和黏液癌并不常见。
我们的数据可能意味着中国人群中HNPCC的特征可能与西方国家不同。应用NCI推荐的标准可能不足以有效地识别中国的HNPCC家系。有必要进行进一步研究以印证或反驳我们的结果，从而使NCI的建议更具普遍适用性。
