由于微衛(wèi)星不穩(wěn)定（MSI）在泛癌種中具有明確且重要的臨床檢測意義，現(xiàn)已被國內(nèi)外眾多臨床指南共識強烈推薦常規(guī)檢測。臨床對于MSI的檢測需求越來越明確，是否檢測MSI現(xiàn)已不再是問題，如何選擇檢測位點給患者帶來最準確的檢測結果才更加需要注意。

人類基因組中已知的微衛(wèi)星位點數(shù)目已有1900萬個[1]，而如何在眾多位點中選擇最具有代表性的微衛(wèi)星位點，國內(nèi)外指南共識其實早有定論。縱觀國內(nèi)外指南，明確推薦用于MSI檢測的Panel都是由五個位點組成，即美國癌癥研究中心（NCI）提出的由兩個單核苷酸位點和三個雙核苷酸位點組成的2B3D NCI Panel（BAT-26、BAT-25、D5S346、D2S123、D17S250）和由5個單核苷酸位點組成的Promega Panel。并且，5個位點的判定標準也是一致的：5個位點中，2個及以上的位點不穩(wěn)定為MSI-H；5個位點中1個位點不穩(wěn)定為MSI-L，5個位點均穩(wěn)定為MSS[2]。目前沒有任何指南推薦6個及6個以上的單核苷酸位點。

圖 1 NCCN指南明確推薦5個位點組成的兩套Panel以及判定標準

指南共識所推薦的兩套位點中，2B3D NCI Panel從被提出以來一直被指南共識所推薦，其推薦地位從未被動搖。而5個單核苷酸位點Panel還是經(jīng)過了較為復雜的演進過程，最初是法國人類多態(tài)性研究中心基于高加索人群數(shù)據(jù)提出的Pentaplex Panel（BAT25、BAT26、NR-21、NR-22、NR-24）[3]，該Panel被Revised bethesda指南推薦[4]。后來，美國Promega公司在Pentaplex Panel上做了進一步改進，將NR-22替換為Mono-27推出了Promega Panel（BAT-25、BAT-26、NR-21、NR-24、MONO-27）。基于此，NCCN指南推薦2B3D NCI Panel和以Promega Panel為主的5個單核苷酸位點Panel用于MSI檢測，而沒有任何指南推薦6個單核苷酸位點。

表 1 不同檢測Panel指南推薦與臨床研究應用情況

同時，國內(nèi)外各種PD-1/L1免疫檢查點抑制劑的大型臨床研究入組MSI-H患者的篩選位點都遵循了指南推薦，選擇的2B3D NCI Panel或Promega Panel由5個位點組成的檢測Panel，比如帕博利珠單抗的臨床研究中以上兩種Panel都使用過；納武利尤單抗、阿維魯單抗、德瓦魯單抗的臨床研究則更多使用的是2B3D NCI Panel。而目前公開的數(shù)據(jù)和研究中，沒有任何臨床研究是用的是5個位點以上的MSI檢測Panel。因此，6個位點的檢測Panel并沒有免疫治療伴隨診斷的數(shù)據(jù)支持。

圖 2 大型臨床研究采用5個位點的2B3D NCI Panel或單核苷酸位點

近日，市面上有些聲音將某個由6個單核苷酸位點組成的Panel與指南共識推薦和臨床研究中使用的Pentaplex Panel或Promega Panel混同，企圖混淆視聽?？梢栽敿毐容^一下Pentaplex Panel、Promega Panel 和6個單核苷酸的Panel。

表 2 單核苷酸Panel位點信息

可以看出，6個單核苷酸位點與Pentaplex相比，少了NR-22位點，且多了NR-27和MONO-27位點，同時也比Promega Panel多一個NR-27位點。而基于國內(nèi)人群不同檢測Panel的MSI-H檢出率的META分析結果顯示，6個單核苷酸位點Panel的MSI-H整體檢出率遠低于5個單核苷酸的Promega Panel，所有組合中，檢出率最高的還是2B3D NCI Panel[9]。

表 3 中國人群不同MSI檢測Panel檢出率匯總

那么同樣是單核苷酸Panel，為什么6個單核苷酸比Promega的檢出率低呢？我們發(fā)現(xiàn)，6個單核苷酸位點相比Promega位點多出了NR-27位點，這個位點是從哪里來的呢？我們在這一篇發(fā)表于Disease Markers（影響因子=3.434）雜志的文獻中，發(fā)現(xiàn)了NR-27的選擇原因。

圖 3 由于NR22位點無法兼容，NR27位點引入Pentaplex Panel

在20年前，我們進行MSI檢測時，大多是進行的單重PCR，操作是較為復雜的，于是研究者們希望能夠開發(fā)多重PCR在一個單管中完成多個微衛(wèi)星位點的檢測進而簡化流程。但是，在將Pentaplex Panel與多重PCR技術結合時，研究團隊發(fā)現(xiàn)NR-22位點無法與其余四個位點在同一個單管中兼容，因此將NR-27位點引入，替代了Pentaplex的NR-22位點[24]。但是原文中，并沒有闡述為什么會選擇NR-27，也并沒有對NR-27在人群中的敏感性。

這個NR-27位點在中國人群中并沒有公開的研究數(shù)據(jù)或文獻報道來證實其檢測性能。而基于國外人群數(shù)據(jù)顯示，NR-27位點的檢測敏感性僅6%左右[25]，6個位點組合加入NR-27位點很有可能會降低檢測Panel的整體敏感性。并且6個單核苷酸位點的判讀標準是不明確的，因為指南中根本沒有推薦過任何大于5個位點的檢測Panel。這些因素有可能就是6個單核苷酸位點MSI-H檢出率相較5個位點的組合更低，更容易造成漏檢的原因。

圖 4 數(shù)據(jù)提示NR-27位點靈敏度不高

綜上，無論是經(jīng)典2B3D還是單核苷酸位點組合，指南推薦和有數(shù)據(jù)驗證的主流位點都是5個位點組成的Panel，6個位點的檢測panel沒有任何指南推薦，且無任何伴隨診斷的用藥的數(shù)據(jù)基礎。

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