Objective: To analyze the microsatellite instability (MSI) status in endometrioid endometrial carcinoma (EEC) with deficient mismatch repair (dMMR) and to explore the concordance between MSI next generation sequencing (NGS)/PCR and MMR immunohistochemistry (IHC) results. Methods: Sixty dMMR EEC cases by IHC from November 2017 to February 2019 were selected in the Department of Pathology, Peking Union Medical College Hospital. Two pathologists reviewed the IHC results. The MSI status and the germline/somatic mutational status of MMR genes were analyzed by NGS. MLH1 promoter methylation status was determined by methylation-specific PCR (MSP) in cases with MLH1 protein deficiency. In cases with discrepant results between MMR IHC and MSI NGS, the MSI status was detected again by PCR, and the reasons for the discrepancy were discussed with gene mutation and MLH1 promoter methylation results. Results: Among 60 dMMR EEC specimens, 3 samples were re-assigned as proficient mismatch repair (pMMR) after pathological review, and identified as MSS by NGS. Another 3 dMMR cases showed MSI-uncertainty (MSI-U) by NGS due to insufficient tumor content. In the remaining 54 cases, the concordance between MMR IHC and MSI NGS was 87% (47/54). The seven discrepant cases was further analyzed: in 5 discrepant cases with MLH1/PMS2 protein loss, one case did not have enough samples for detection, one case was MSI-H, and the remaining three cases were MSS by PCR. All these 5 cases with MLH1/PMS2 protein loss showed the MLH1 promoter hypermethylation, two of which also had a somatic mutation in the MSH2 gene. The two discrepant cases with MSH6 protein loss were both MSS by PCR, one of which was considered to have Lynch syndrome with germline mutation in MSH6 gene. Conclusions: Although the overwhelming majority of dMMR EEC cases by IHC shows MSI-H by NGS/PCR, there are uncommon discrepant dMMR EEC cases with MSS. They are mostly found in cases with MLH1/PMS2 protein loss caused by MLH1 promoter hypermethylation and rarely related to Lynch syndrome. Both MMR IHC and MSI NGS/PCR tests have their advantages and disadvantages, complimentary to each other.
目的： 了解免疫组织化学（IHC）结果为错配修复缺陷（dMMR）的子宫内膜样腺癌（EEC）中微卫星不稳定（MSI）状态，探讨在EEC中MMR/MSI不同检测方法间一致性及各自的优缺点。 方法： 选取2017年11月至2019年2月北京协和医院病理科错配修复（MMR）蛋白IHC检测结果为dMMR的EEC病例60例，由2名病理医师对IHC结果进行复核。利用二代测序（NGS）技术对60例样本进行MSI状态及MMR基因胚系/体细胞突变状态的检测。MLH1蛋白表达缺失的病例用甲基化特异性PCR（MSP）技术检测MLH1启动子甲基化状态。在MMR IHC和MSI NGS检测结果不相符的样本中，用PCR法再次检测MSI状态，并结合基因突变及MLH1启动子甲基化检测探讨结果不一致的原因。 结果： 在IHC结果为dMMR的60例EEC样本中，3例IHC结果经复核为MMR蛋白表达完整/正常（pMMR），相应NGS检测结果均为MSS；另有3例肿瘤细胞含量不足，NGS检测结果为MSI状态不能确定（MSI-U）。其余54例中，dMMR与MSI-H的符合率为87%（47/54）。对7例不符合样本进一步分析发现：（1）5例为MLH1/PMS2蛋白表达共缺失病例。除1例样本量过少外，4例经PCR法再次检测MSI状态，其中1例为MSI-H，余3例为MSS；5例均为MLH1启动子高甲基化状态，其中2例MSS病例还存在MSH2基因的体细胞突变。（2）2例为MSH6蛋白表达单独缺失病例。2例PCR法检测结果均为MSS，其中1例存在MSH6基因胚系突变，考虑为Lynch综合征。 结论： 在IHC检测结果为dMMR的EEC中，除去IHC判读以及肿瘤含量不足的因素外，绝大多数病例NGS/PCR检测结果为MSI-H，一致性较高。但的确存在少数IHC结果为dMMR EEC的病例表现为MSS，多见于MLH1启动子高甲基化状态造成的MLH1/PMS2蛋白表达共缺失病例，罕见于Lynch综合征相关病例。MMR IHC和MSI NGS/PCR检测方法各有优缺点，必要时可以互为补充。.