[Comprehensive assessment of mismatch repair and microsatellite instability status in molecular classification of endometrial carcinoma].

Objective: To explore the concordance and causes of different mismatch repair (MMR) and microsatellite instability (MSI) detection results in endometrial carcinoma (EC) molecular typing. Methods: A total of 214 EC patients diagnosed from January 2021 to April 2023 were selected at the Department of Pathology, Peking University Third Hospital. The immunohistochemistry (IHC) results of MMR protein were reviewed. Tumor specific somatic mutations, MMR germline mutations, microsatellite scores and tumor mutation burden (TMB) were detected by next-generation sequencing (NGS) with multi-gene panel. Methylation-specific PCR was used to detect the methylation status of MLH1 gene promoter in cases with deficient MLH1 protein expression. In cases with discrepant results between MMR-IHC and MSI-NGS, the MSI status was detected again by PCR (MSI-PCR), and the molecular typing was determined by combining the results of TMB and MLH1 gene promoter methylation. Results: (1) In this study, there were 22 cases of POLE gene mutation subtype, 55 cases of mismatch repair deficient (MMR-d) subtype, 29 cases of p53 abnormal subtype, and 108 cases of no specific molecular profile (NSMP). The median age at diagnosis of MMR-d subtype (54 years old) and the proportion of aggressive histological types (40.0%, 22/55) were higher than those of NSMP subtype [50 years old and 12.0% (13/108) respectively; all P<0.05]. (2) Among 214 patients, MMR-IHC test showed that 153 patients were mismatch repair proficient (MMR-p), 49 patients were MMR-d, and 12 patients were difficult to evaluate directly. MSI-NGS showed that 164 patients were microsatellite stable (MSS; equal to MMR-p), 48 patients were high microsatellite instability (MSI-H; equal to MMR-d), and 2 patients had no MSI-NGS results because the effective sequencing depth did not meet the quality control. The overall concordance between MMR-IHC and MSI-NGS was 94.3% (200/212). All the 12 discrepant cases were MMR-d or subclonal loss of MMR protein by IHC, but MSS by NGS. Among them, 10 cases were loss or subclonal loss of MLH1 and (or) PMS2 protein. Three discrepant cases were classified as POLE gene mutation subtype. In the remaining 9 cases, 5 cases and 3 cases were confirmed as MSI-H and low microsatellite instability (MSI-L) respectively by MSI-PCR, 6 cases were detected as MLH1 gene promoter methylation and 7 cases demonstrated high TMB (>10 mutations/Mb). These 9 cases were classified as MMR-d EC. (3) Lynch syndrome was diagnosed in 27.3% (15/55) of all 55 MMR-d EC cases, and the TMB of EC with MSH2 and (or) MSH6 protein loss or associated with Lynch syndrome [(71.0±26.2) and (71.5±20.1) mutations/Mb respectively] were significantly higher than those of EC with MLH1 and (or) PMS2 loss or sporadic MMR-d EC [(38.2±19.1) and (41.9±24.3) mutations/Mb respectively, all P<0.01]. The top 10 most frequently mutated genes in MMR-d EC were PTEN (85.5%, 47/55), ARID1A (80.0%, 44/55), PIK3CA (69.1%, 38/55), KMT2B (60.0%, 33/55), CTCF (45.5%, 25/55), RNF43 (40.0%, 22/55), KRAS (36.4%, 20/55), CREBBP (34.5%, 19/55), LRP1B (32.7%, 18/55) and BRCA2 (32.7%, 18/55). Concurrent PTEN, ARID1A and PIK3CA gene mutations were found in 50.9% (28/55) of MMR-d EC patients. Conclusions: The concordance of MMR-IHC and MSI-NGS in EC is relatively high.The discordance in a few MMR-d EC are mostly found in cases with MLH1 and (or) PMS2 protein loss or MMR protein subclonal staining caused by MLH1 gene promoter hypermethylation. In order to provide accurate molecular typing for EC patients, MLH1 gene methylation, MSI-PCR, MMR gene germline mutation and TMB should be combined to comprehensively evaluate MMR and MSI status.目的： 探讨不同的错配修复（MMR）蛋白和微卫星不稳定性（MSI）状态检测方法在子宫内膜癌分子分型中的一致性及差异原因。 方法： 收集2021年1月至2023年4月北京大学第三医院病理科诊断的214例子宫内膜癌患者，对其MMR蛋白的免疫组化（MMR-IHC）检测结果进行复核，通过二代测序（NGS）技术进行MSI状态（MSI-NGS）及多基因体细胞突变、胚系MMR基因突变检测，计算肿瘤突变负荷（TMB）值。对MMR-IHC检测与MSI-NGS检测结果不相符的患者进一步进行MSI-PCR检测和MLH1基因启动子甲基化检测，并结合TMB值综合评估MMR、MSI状态，明确分子分型。 结果： （1）214例子宫内膜癌患者中，POLE突变（POLEmut）型22例，错配修复缺陷（MMR-d）型55例，p53异常（p53abn）型29例，无特殊分子改变（NSMP）型108例。其中，MMR-d型患者的中位确诊年龄为54岁、侵袭性病理亚型（包括子宫内膜样癌G3和非子宫内膜样癌）的比例为40.0%（22/55），均高于NSMP型［分别为50岁、12.0%（13/108）］，两者分别比较，差异均有统计学意义（P均<0.05）。（2）214例患者中，MMR-IHC检测显示，153例患者判定为错配修复正常（MMR-p），49例判定为MMR-d，12例患者难以直接判读；MSI-NGS检测显示，164例患者判定为微卫星稳定性（MSS；与MMR-p对应），48例患者判定为高度微卫星不稳定性（MSI-H；与MMR-d对应），2例患者因有效测序深度未满足质控标准而无MSI结果。MMR-IHC检测与MSI-NGS检测结果的一致率为94.3%（200/212），12例不符合患者的MMR-IHC检测结果为MMR-d或亚克隆缺失，但MSI-NGS检测均判定为MSS，其中MLH1和PMS2蛋白表达共缺失或亚克隆缺失10例。12例不符合患者中，3例检出POLE基因致病性突变而归为POLE突变型；另外9例患者中，8例有MSI-PCR检测结果的患者中5例为MSI-H、3例为低度微卫星不稳定性（MSI-L），7例TMB值高于10个突变/Mb，6例检出MLH1基因启动子甲基化，综合分析后9例患者均判定为MMR-d。（3）55例MMR-d型子宫内膜癌患者中，15例（27.3%，15/55）确诊为Lynch综合征。15例Lynch综合征相关MMR-d型子宫内膜癌患者的TMB值［（71.5±20.1）个突变/Mb］显著高于40例散发性MMR-d型子宫内膜癌患者［（41.9±24.3）个突变/Mb；t=3.51，P=0.001］；20例MSH2和（或）MSH6蛋白表达缺失患者的TMB值［（71.0±26.2）个突变/Mb］显著高于35例MLH1和（或）PMS2蛋白表达缺失者［（38.2±19.1）个突变/Mb；t=-4.71，P<0.001］。55例MMR-d型子宫内膜癌患者中，突变率排序前10个的基因是PTEN（85.5%，47/55）、ARID1A（80.0%，44/55）、PIK3CA（69.1%，38/55）、KMT2B（60.0%，33/55）、CTCF（45.5%，25/55）、RNF43（40.0%，22/55）、KRAS（36.4%，20/55）、CREBBP（34.5%，19/55）、LRP1B（32.7%，18/55）、BRCA2（32.7%，18/55）基因，其中PTEN、ARID1A、PIK3CA基因共突变率为50.9%（28/55）。 结论： MMR-IHC检测与MSI-NGS检测结果的—致率较高，两种方法检测结果不一致多见于MLH1基因启动子高甲基化状态导致的MLH1和PMS2蛋白表达共缺失或MMR蛋白亚克隆缺失，必要时应结合MLH1基因甲基化、MSI-PCR、MMR基因胚系突变及TMB值综合评估MMR、MSI状态，为子宫内膜癌患者提供精准的分子分型。.