Kang So Young, Kim Deok Geun, Ahn Soomin, Ha Sang Yun, Jang Kee-Taek, Kim Kyoung-Mee
Department of Pathology and Translational Genomics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea.
Department of Clinical Genomic Center, Samsung Medical Center, Seoul, Republic of Korea; Department of Digital Health, Samsung Advanced Institute of Health Science and Technology, Sungkyunkwan University, Seoul, Republic of Korea.
Pathol Res Pract. 2022 May;233:153874. doi: 10.1016/j.prp.2022.153874. Epub 2022 Apr 4.
Checkpoint inhibitor approval for microsatellite instability-high (MSI-H) tumours has made MSI as a therapeutically important biomarker. Next-generation sequencing (NGS)-based MSI detection is being widely used for assessing MSI. However, MSI tumours detected using NGS and their relevance to MSI-polymerase chain reaction (PCR) and mismatch repair deficiency (dMMR) are unclear. In 1942 solid cancer cases tested using NGS-based comprehensive cancer panel with 523 genes (1.94 mb), the MSI score, tumour mutation burden (TMB; ≥ 10 mutations/mb), and frameshift mutations were analysed. GeneScan analyses of five mononucleotide markers (MSI-PCR) and MMR protein immunohistochemistry (IHC) were compared with the NGS-MSI results. With a ≥ 12% MSI score as a cut-off for MSI-H, two MSS cases were classified as MSI-H. With a ≥ 20% cut-off, 10 cases categorised as MSS by NGS were MSI-H/dMMR by MSI-PCR and MMR IHC. To avoid discrepant cases, we adopted a high MSI cut-off and a borderline MSI category. Finally, MSI-H (≥ 20%), borderline MSI (≥ 7% and < 20%), and MSS (< 7%) were found in 35 (1.8%), 24 (1.2%), and 1883 (97%) cases, respectively. All MSI-H cases by NGS were MSI-H/dMMR by MSI-PCR and MMR IHC. Of the 24 borderline MSI cases by NGS, MSI-H/dMMR was 9 (37.5%) cases, MSS/dMMR was 1 (4.2%) case, and 11 (45.8%) of them had high TMB. All MSS cases by NGS were MSS/pMMR by MSI-PCR/IHC, and 257 (13.6%) had high TMB. With those arbitrary cut-off points, 10 (0.5%) MSS cases using NGS were discrepant with MSI-PCR or MMR IHC, and all were borderline MSI cases. The mean number of frameshift mutations was significantly higher in the MSI-H group (28.3) than in the borderline MSI (7.7) or MSS (1.3) groups (p < 0.001). In conclusion, to facilitate therapeutic decision-making for NGS, cut-off points for MSI can be defined based on MSI-PCR/dMMR confirmation.
针对微卫星高度不稳定（MSI-H）肿瘤的检查点抑制剂获批，使得MSI成为一个具有重要治疗意义的生物标志物。基于二代测序（NGS）的MSI检测正被广泛用于评估MSI。然而，使用NGS检测出的MSI肿瘤及其与MSI-聚合酶链反应（PCR）和错配修复缺陷（dMMR）的相关性尚不清楚。在1942例使用包含523个基因（1.94兆碱基）的基于NGS的综合癌症检测板进行检测的实体癌病例中，分析了MSI评分、肿瘤突变负荷（TMB；≥10个突变/兆碱基）和移码突变。将五个单核苷酸标记的基因扫描分析（MSI-PCR）和错配修复蛋白免疫组化（IHC）与NGS-MSI结果进行了比较。以≥12%的MSI评分作为MSI-H的临界值，有2例微卫星稳定（MSS）病例被归类为MSI-H。以≥20%作为临界值，10例经NGS归类为MSS的病例经MSI-PCR和MMR IHC检测为MSI-H/dMMR。为避免出现不一致的情况，我们采用了高MSI临界值和临界MSI类别。最后，分别在35例（1.8%）、24例（1.2%）和1883例（97%）病例中发现了MSI-H（≥20%）、临界MSI（≥7%且<20%）和MSS（<7%）。所有经NGS检测为MSI-H的病例经MSI-PCR和MMR IHC检测均为MSI-H/dMMR。在24例经NGS检测为临界MSI的病例中，MSI-H/dMMR为9例（37.5%），MSS/dMMR为1例（4.2%），其中11例（45.8%）具有高TMB。所有经NGS检测为MSS的病例经MSI-PCR/IHC检测均为MSS/pMMR，257例（13.6%）具有高TMB。采用这些任意临界值时，10例（0.5%）经NGS检测为MSS的病例与MSI-PCR或MMR IHC结果不一致，且均为临界MSI病例。MSI-H组的移码突变平均数量（28.3）显著高于临界MSI组（7.7）或MSS组（1.3）（p<0.001）。总之，为便于基于NGS的治疗决策，可以根据MSI-PCR/dMMR确认来定义MSI的临界值。
