Recent literature suggests a combination of flow cytometric determination of Ki-67 and immunophenotype as a reliable tool to classify canine lymphomas. Immunohistochemistry (IHC) on histological samples is the gold standard technique assessing Ki-67 index. Agreement between IHC and FCM derived Ki-67 indices has never been investigated. The aim of this study was to investigate the agreement between IHC and FCM in the assessment of Ki-67 expression/index, in order to evaluate whether FCM may serve as a non-invasive alternative method for the estimation of proliferative activity in canine lymphoma. Dogs with previously untreated canine lymphoma undergoing diagnostic lymphadenectomy were prospectively enrolled. Ki-67 expression/index was assessed by FCM and IHC and expressed as percentage of positive cells. 39 dogs classified by histopathology matched the inclusion criteria. With both methods, Ki-67 expression/index was higher in intermediate/high-grade lymphomas. Spearman's coefficient of correlation was ρ = 0.57; (95% CI0.33-0.75) suggesting a moderate correlation. A Bland-Altman plot revealed a negative constant bias of −3.55 (95% CI: −10.52 to 3.42) with limits of agreement from −45.71 to 38.61. The study confirmed agreement albeit with wide confidence intervals between the values of Ki-67 expression/index assessed with FCM and IHC. Discrepancies were observed in a subset of cases. Possible explanation could be that Ki-67 index in IHC is determined in the most proliferative areas of the slide, which could introduce kind of sampling bias, whereas FCM evaluates many more cells in cell suspension. Further studies are warranted to investigate this phenomenon.

中文翻译：

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Ki-67 评估——免疫组化和流式细胞术在犬淋巴瘤中的一致性

最近的文献表明将 Ki-67 的流式细胞仪测定和免疫表型相结合作为分类犬淋巴瘤的可靠工具。组织学样本的免疫组织化学 (IHC) 是评估 Ki-67 指数的金标准技术。从未调查过 IHC 和 FCM 衍生的 Ki-67 指数之间的一致性。本研究的目的是调查 IHC 和 FCM 在评估 Ki-67 表达/指数方面的一致性，以评估 FCM 是否可以作为评估犬淋巴瘤增殖活性的非侵入性替代方法。前瞻性招募了接受诊断性淋巴结切除术的先前未治疗的犬淋巴瘤的狗。Ki-67 表达/指数通过 FCM 和 IHC 评估并表示为阳性细胞的百分比。按组织病理学分类的 39 只狗符合纳入标准。使用这两种方法，Ki-67 表达/指数在中/高级淋巴瘤中较高。Spearman 相关系数为ρ  = 0.57；(95% CI0.33-0.75) 表明中度相关性。Bland-Altman 图显示负常数偏差为 -3.55（95% CI：-10.52 至 3.42），一致性范围为 -45.71 至 38.61。该研究证实了一致性，尽管用 FCM 和 IHC 评估的 Ki-67 表达/指数值之间存在很大的置信区间。在部分案例中观察到差异。可能的解释可能是 IHC 中的 Ki-67 指数是在载玻片的最增殖区域确定的，这可能会引入某种采样偏差，而 FCM 评估细胞悬浮液中的更多细胞。需要进一步的研究来调查这种现象。