Lynch综合征（Lynch syndrom）是结直肠癌中最常见的遗传性肿瘤综合征，约占全部大肠癌的2~3%。该病患者同时增加了罹患肠外及第二肿瘤的风险。现已证明，Lynch综合征是由于编码错配修复基因（mismatch repair，MMR）——MLH1，MSH2，MSH6和PMS2的种系突变、失活导致的一类显性遗传性疾病，近年发现EPCAM的突变与MSH2表达缺失相关。尽管有Amsterdan及Bethesda等临床诊断标准，利用分子遗传学检测在MMR基因中发现致病性胚系突变仍为目前诊断Lynch综合征的金标准。对于发病年龄小于70岁的结直肠癌患者，均应进行Lynch综合征的筛查。首先需进行微卫星不稳定性（microsatellites instability，MSI）检测，检测手段包括PCR扩增微卫星位点及免疫组化（IHC）检测，而后对相应的MMR基因进行胚系突变的检测以明确是否为Lynch综合征以及相应的致病位点。对于MLH1表达缺失患者需进行BRAF基因突变检测和（或）MLH1启动子区域甲基化检测以除外散发性结直肠癌。对于确诊的患者建议进行家系筛查并进行规律的监测和随访。

Lynch syndrome is the most common form of hereditary CRC, accounting for approximately 2~3% of population-based CRC. Individuals with Lynch syndrome have an increased risk for extracolonic cancer and second primary colorectal cancer. It has been dedicated that Lynch syndrome is an autosomal dominant cancer predisposition syndrome caused by germline mutations in the DNA mismatch repair genes (MMR)—MLH1, MSH2, MSH6 and PMS2, and EPCAM mutation is also found associated with MSH2 deficiency recently. Even though clinical diagnostic criteria (Amsterdan I/II, revised Bethesda) have been released decades ago, molecular testing of MMR genes is still the golden standard of Lynch syndrome diagnosis. Colorectal cancer patients less than 70y, are recommended to get into the procedure of Lynch syndrome screening, starting with microsatellite instability and/or immunohistochemical analysis on the tumor specimen followed by germline genetic testing and possibly further studies, such as MLPA. Notably, Testing on BRAF mutation is necessary, when the expression of MLH1 is lost, in order to exclude the sporadic colorectal cancer. Individuals with identified germline mutations need further screening for their immediate relatives.