Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York.
Cancer Cytopathol. 2019 Oct;127(10):643-649. doi: 10.1002/cncy.22170. Epub 2019 Aug 9.
The Ki-67 proliferation marker has multiple diagnostic and prognostic applications. Although several clones to the Ki-67 antigen are commercially available, the MIB1 clone is widely recommended in the surgical pathology literature for neuroendocrine tumors. In our cytopathology practice, we have encountered unexpectedly low MIB1 immunoreactivity in CytoLyt-fixed cell blocks (CBs). The current study evaluated the impact of fixatives, CB processing, and immunocytochemical (ICC) procedures on Ki-67 immunoreactivity.
Test CBs were prepared from freshly resected tumors, and multiple variables in the MIB1 ICC procedure were tested, including CytoLyt versus formalin collection media, MIB1 versus other Ki-67 clones including 30-9, and other variables. MIB1 versus Ki-67 30-9 clones were tested in parallel on CytoLyt-fixed CBs from clinical samples of small cell lung carcinoma (SCLC).
In the test CBs (n = 10), the mean MIB1 labeling index was 10% in CytoLyt versus 47% in formalin (P = .0116), with a mean loss of reactivity in matched CBs of 37% (up to 70%). None of the procedure modifications tested in 223 individual ICC reactions recovered MIB1 reactivity in CytoLyt except for switching to the Ki-67 30-9 antibody. In CytoLyt-fixed SCLC samples (n = 14), the Ki-67 30-9 antibody demonstrated expected ranges of reactivity (mean, 83%; range, 60%-100%), whereas MIB1 demonstrated markedly inhibited labeling (mean, 60%; range, 10%-95%) (P = .0058).
CytoLyt fixation substantially inhibits MIB1 immunoreactivity, whereas the Ki-67 30-9 clone is not susceptible to inhibition. Markedly discrepant MIB1 reactivity may present a pitfall in the diagnosis of SCLC and may lead to the incorrect prognostic stratification of other tumor types. For laboratories using CytoLyt, we recommend using the Ki-67 30-9 antibody rather than the MIB1 antibody.
Ki-67 增殖标志物具有多种诊断和预后应用。尽管有多个针对 Ki-67 抗原的克隆可供商业使用，但 MIB1 克隆在神经内分泌肿瘤的外科病理学文献中被广泛推荐。在我们的细胞病理学实践中，我们遇到了出乎意料的低 CytoLyt 固定细胞块 (CB) 中的 MIB1 免疫反应性。本研究评估了固定剂、CB 处理和免疫细胞化学 (ICC) 程序对 Ki-67 免疫反应性的影响。
测试 CB 是从新切除的肿瘤中制备的，并且测试了 MIB1 ICC 程序中的多个变量，包括 CytoLyt 与福尔马林收集介质、MIB1 与包括 30-9 在内的其他 Ki-67 克隆以及其他变量。在来自小细胞肺癌 (SCLC) 的临床样本的 CytoLyt 固定 CB 上同时测试了 MIB1 与 Ki-67 30-9 克隆。
在测试 CB（n=10）中，MIB1 标记指数在 CytoLyt 中为 10%，在福尔马林（P=0.0116）中为 47%，在匹配的 CB 中平均反应性丧失 37%（高达 70%）。除了切换到 Ki-67 30-9 抗体外，在 223 个单独的 ICC 反应中测试的所有程序修改均未恢复 CytoLyt 中的 MIB1 反应性。在 CytoLyt 固定的 SCLC 样本（n=14）中，Ki-67 30-9 抗体显示出预期的反应范围（平均，83%；范围，60%-100%），而 MIB1 显示出明显抑制的标记（平均，60%；范围，10%-95%）（P=0.0058）。
CytoLyt 固定剂会显著抑制 MIB1 免疫反应性，而 Ki-67 30-9 克隆则不易受到抑制。明显不一致的 MIB1 反应性可能会在 SCLC 的诊断中出现陷阱，并可能导致其他肿瘤类型的错误预后分层。对于使用 CytoLyt 的实验室，我们建议使用 Ki-67 30-9 抗体而不是 MIB1 抗体。
