子宫内膜癌微卫星不稳定性分析:微小微卫星变换的意义

Analysis of microsatellite instability in endometrial cancer:The significance of minimal microsatellite shift

目的:对比结直肠癌(colorectal cancer,CRC),评估子宫内膜癌(endometrial cancer,EMC)微卫星不稳定性(microsatellite instability,MSI)改变的特点。方法:收集228例EMC和770例CRC进行对比分析。采用免疫组织化学(immunohistochemistry,IHC)方法检测错配修复缺陷(deficient mismatch repair,dMMR)蛋白表达缺失,采用PCR及毛细管电泳片段分析法检测MSI(MSI-PCR),MSI-PCR采用5个单核苷酸位点(BAT-25、BAT-26、NR-21、NR-24和MONO-27)。结果:EMC中,27.19%(62/228例)为dMMR,显著高于CRC(7.79%,60/770例),且4例dMMR-EMC和2例dMMR-CRC呈错配修复(mismatch repair,MMR)蛋白亚克隆表达。MSI-PCR检测依据显著微卫星变换判读标准,EMC的结果显示:16.23%(37/228例)为高度MSI,2.63%(6/228例)为低度MSI,81.14%(185/228例)为微卫星稳定型,MMR-IHC与MSI-PCR两种评估方法的不一致率为11.84%(27/228例);CRC的结果显示:8.05%(62/770例)为高度MSI,0.13%(1/770例)为低度MSI,91.82%(707/770例)为微卫星稳定型,两种评估方法的不一致率仅为0.52%(4/770例)。而依据微小微卫星变换结果判读,12例EMC发现微小微卫星变换(8例dMMR/微卫星稳定型和4例dMMR/低度MSI),被评估为dMMR/高度MSI,因此,高度MSI型EMC为21.49%(49/228例),两种方法的不一致率降至6.58%(15/228例)。CRC中未见微小微卫星变换。与显著微卫星变换EMC组相比,微小微卫星变换EMC组的患者年龄偏小,肿瘤分化更好,国际妇产科联盟(International Fede-ration of Gyne-cology and Obstetrics,FIGO)分期更早。两组间组织学类型及FIGO分期的差异有统计学意义(P<0.001,P=0.006)。结论:EMC易发生微小微卫星变换,MSI-PCR检测结果的判读不应忽视微小微卫星变换,MMR-IHC和MSI-PCR互补联合检测是捕获dMMR肿瘤最敏感和特异的方法。

Objective:To analyze the differences and characteristics of microsatellite instability(MSI)in endometrial cancer(EMC),by using colorectal cancer(CRC)as control.Methods:In the study,228 cases of EMC were collected.For comparative analysis,770 cases of CRC were collected.Mismatch repair(MMR)expression was detected by immunohistochemistry(IHC),and microsatellite instability(MSI)was analyzed by PCR and capillary electrophoresis fragment analysis(MSI-PCR).MSI-PCR was detected using five mononucleotide repeat markers:BAT-25,BAT-26,NR-21,NR-24,and MONO-27.Results:In EMC,we found 27.19%(62/228)of deficient mismatch repair(dMMR)using IHC,significantly higher than CRC(7.79%,60/770).Meanwhile,subclonal expression of MMR protein was found in 4 cases of dMMR-EMC and 2 cases of dMMR-CRC.According to the criteria of major micro-satellite shift,we found 16.23%(37/228)of MSI-high(MSI-H),2.63%(6/228)of MSI-low(MSI-L),and 81.14%(185/228)of microsatellite stability(MSS)in EMC using MSI-PCR.The discor-dance rate between MMR-IHC and MSI-PCR in EMC was 11.84%(27/228).In CRC,we found 8.05%(62/770)of MSI-H,0.13%(1/770)of MSI-L,and 91.82%(707/770)of MSS.The discordance rate between MMR-IHC and MSI-PCR in CRC was only 0.52%(4/770).However,according to the criteria of minimal microsatellite shift,12 cases of EMC showed minimal microsatellite shift including 8 cases of dMMR/MSS and 4 cases of dMMR/MSI-L and these cases were ultimately evaluated as dMMR/MSI-H.Then,21.49%(49/228)of EMC showed MSI-H and the discordance rate MMR-IHC and MSI-PCR in EMC decreased to 6.58%(15/228).No minimal microsatellite shift was found in CRC.Compared with EMC group with major microsatellite shift,cases with minimal microsatellite shift showed younger age,better tumor differentiation,and earlier International Federation of Gynecology and Obstetrics(FIGO)stage.There were significant differences in histological variant and FIGO stage between the two groups(P<0.001,P=0.006).Conclusion:EMC was more prone to minimal microsatellite shift,which should not be ignored in the interpretation of MSI-PCR results.The combined detection of MMR-IHC and MSI-PCR is the most sensitive and specific method to capture MSI tumors.