Institute of Pathology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
Institute of Pathology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
Urol Oncol. 2020 May;38(5):488-495. doi: 10.1016/j.urolonc.2019.12.012. Epub 2020 Feb 14.
Microsatellite instability (MSI), a hypermutator phenotype described in many cancers, has emerged as a predictive biomarker for immune checkpoint inhibitor therapy. Cancer heterogeneity represents a potential obstacle for the analysis of predicitive biomarkers. MSI has been reported in bladder cancer, but data on the possible extent of intratumoral heterogeneity are lacking.
To study MSI heterogeneity in bladder cancer, a tissue microarray (TMA) comprising 598 muscle-invasive urothelial carcinomas of the bladder was utilized to screen for MSI by immunhistochemistry with antibodies for MLH1, PMS2, MSH2, and MSH6.
In 9 cases suspicious for MSI, MMR status was further evaluated by large section examination and polymerase chain reaction (PCR)-based analysis of microsatellites ("Bethesda panel") resulting in the identification of 5 validated MSI cases from 448 interpretable cancers (prevalence 1.1%). MMR deficiency always involved PMS2 loss, in 3 cases with additional loss or reduction of MLH1 expression. Four cancers were MSI-high and 1 was MSI-low in the PCR analysis. Parallel sequencing revealed an inactivating MLH1 mutation in 1 tumor but no further known pathogenic MMR gene mutations were found. Immunostaining of all available 72 cancer-containing tissue blocks of the 5 confirmed bladder cancer with MSI including prior and subsequent biopsies showed complete homogeneity of the MMR protein defects and the status of the 4 MMR proteins did not markedly change in sequential resections. In all 4 cases with noninvasive precursor lesions, MSI was also detectable.
These data suggest that MSI occurs early in invasive bladder cancer and immunohistochemical MMR analysis on limited biopsy material is sufficient to estimate MMR status of the entire cancer mass.
微卫星不稳定性（MSI）是一种在许多癌症中出现的超突变表型，已成为免疫检查点抑制剂治疗的预测生物标志物。癌症异质性代表了分析预测生物标志物的潜在障碍。MSI 已在膀胱癌中报道，但关于肿瘤内异质性的可能程度的数据尚缺乏。
为了研究膀胱癌中的 MSI 异质性，使用组织微阵列（TMA）对 598 例肌肉浸润性膀胱癌进行免疫组织化学分析，用 MLH1、PMS2、MSH2 和 MSH6 抗体筛选 MSI。
在 9 例可疑 MSI 的病例中，通过大切片检查和基于聚合酶链反应（PCR）的微卫星分析（“贝塞斯达面板”）进一步评估 MMR 状态，从而在 448 例可解释的癌症中鉴定出 5 例经证实的 MSI 病例（患病率为 1.1%）。MMR 缺陷总是涉及 PMS2 缺失，在 3 例中伴有 MLH1 表达缺失或减少。4 例癌症在 PCR 分析中为 MSI-高，1 例为 MSI-低。平行测序在 1 例肿瘤中发现了 MLH1 失活突变，但未发现其他已知的致病性 MMR 基因突变。对 5 例经证实的膀胱癌（包括之前和之后的活检）的所有 72 个包含肿瘤的组织块进行免疫组化染色，所有组织块的 MMR 蛋白缺陷完全同质，4 种 MMR 蛋白的状态在连续切除中没有明显改变。在所有 4 例非浸润性前体病变中，也可检测到 MSI。
这些数据表明，MSI 发生在浸润性膀胱癌早期，对有限的活检材料进行免疫组化 MMR 分析足以估计整个肿瘤的 MMR 状态。
