Merkel cell carcinoma (MCC) is in humans and cats a malignant cutaneous neuroendocrine carcinoma, whereas in dogs it possibly has a more benign behaviour. It may be cytologically confused with round cell tumours such as lymphoma because of its striking cytomorphologic similarity. Although MCC is considered to arise from Merkel cells, recent findings indicated that primitive (epi‐)dermal stem cells, early B‐cells or dermal fibroblasts were the origin of human MCC. The aim of our study was to evaluate a possible lymphoid origin in feline and canine MCCs. Specific analysis of CD3, PAX‐5, KIT and PARR assay were performed in 3 feline and 3 canine MCCs. All MCCs (6/6) were negative for CD3 and PAX‐5. KIT was expressed in all MCCs (6/6). Assessment of clonality by PARR assay exhibited a polyclonal B‐ and T‐cell receptor rearrangement in all five cases tested. In conclusion, a lymphoid origin of feline and canine MCCs could not be demonstrated. This is in contrast with human MCCs, that often express early B‐cell lineage markers.

中文翻译：

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猫和犬默克尔细胞癌：病例系列和细胞起源的讨论

默克尔细胞癌 (MCC) 在人类和猫中是一种恶性皮肤神经内分泌癌，而在狗中它可能具有更良性的行为。由于其惊人的细胞形态学相似性，它可能在细胞学上与淋巴瘤等圆形细胞肿瘤相混淆。尽管 MCC 被认为是由默克尔细胞产生的，但最近的研究结果表明，原始（表）真皮干细胞、早期 B 细胞或真皮成纤维细胞是人类 MCC 的起源。我们研究的目的是评估猫和犬 MCC 中可能的淋巴起源。在 3 只猫和 3 只犬 MCC 中进行了 CD3、PAX-5、KIT 和 PARR 测定的特异性分析。所有 MCC (6/6) CD3 和 PAX-5 均为阴性。KIT 在所有 MCC (6/6) 中表达。通过 PARR 分析评估的克隆性在所有 5 个测试病例中都显示出多克隆 B 细胞和 T 细胞受体重排。总之，无法证明猫和犬 MCC 的淋巴起源。这与人类 MCC 形成对比，后者通常表达早期 B 细胞谱系标记。