IMMUN OHI STO CHE MISTRY IN EQUINE PATHOLOGY
indicates indeed the embryologic origin of the clonal neoplastic cell population. Numerous antibodies can be used as markers for equine neoplasms and are working in FFPE equine tissues. In Figure 1 , the most used markers and the most frequent tumours are schematised. Cytokeratins are a large group of cytoskeletal proteins expressed
in any epithelial cells. The most used antibody is a monoclonal one, the AE1/AE3, which is characterised by a mix of antibodies reacting against high and low molecular weight cytokeratins, labelling almost all epithelia (and therefore commonly called “pan- cytokeratin” anti- body). Despite the lack of a strict specificity for some epithelia, the pan- cytokeratin antibody is a very useful one as it can highlight any type of epithelial cells (either normal or neoplastic), even when tu- mours are poorly differentiated. This antibody can label all adenomas, carcinomas (including squamous cell carcinoma) and thymoma but it cannot identify which type of epithelial tumour (e.g. distinguishing an intestinal adenocarcinoma from mammary carcinoma): for this rea- son, in case of carcinomas of unknown primary (CUPs), this antibody can help poorly in determining the primary site. IHC targeting pan- cytokeratin is also very useful when assessing metastasis of carcino- mas in lymph nodes, where no epithelial cells are normally present. Vimentin, on the contrary, is a cytoskeletal protein present in all
mesenchymal cells, which usually labels all cells not labelled by the pan- cytokeratin antibody. This feature makes this protein expressed by a large number of cells and tissue, with only a few exceptions. For this reason, we consider that vimentin is an antibody useful only when in combination with pan- cytokeratin (when distinguishing poorly
Pan-CK
SCC Other carcinomas
Mesothelioma Thymoma Sarcomas (e.g. fibrosarcoma, myxosarcoma )
| 13
differentiated tumours): vimentin IHC does not indeed give much more information apart from confirming the mesenchymal origin of tumour. Mesotheliomas (and normal mesothelial cells) are somehow an
exception from other tumours (and cells) as they both express cyto- keratin and vimentin antigens. Rare reports of this tumour have been reported in the equine species (Dobromylskyj et al., 2011 ). It should be noted that in very poorly differentiated carcinomas, vimentin can be re- expressed in a mechanism called epithelial to mesenchymal transi- tion, which is a feature of the anaplastic transformation of a tumour. Equine sarcoids are difficult (if not impossible) to distinguish from
other mesenchymal cutaneous tumours. The difficulties reside in that bovine papillomaviruses ' DNA can be detected in normal skin (Bogaert et al., 2005 ) and also in other mesenchymal equine tumours (Epperson & Castleman, 2017 ); furthermore, there are no specific IHC markers able to distinguish equine sarcoids from other mesenchymal tumours. Equine sarcoids are vimentin- positive and are known to also express some IHC markers variably including alpha- smooth actin and, rarely, S- 100 (Martano et al., 2016 ; Ogłuszka et al., 2021 ). The most common markers for muscular tumours remain alpha
smooth muscular actin (ASMA) and desmin. Both should be able to label smooth muscle and myoepithelial cells (ASMA) and any type of muscular cells, respectively (Knottenbelt et al., 2016a ); nonethe- less, distinction between smooth muscle tumours (leiomyoma/leio- myosarcoma) and striated muscle ones, is usually more reliable using morphology than immunohistochemistry. There are indeed numer- ous other mesenchymal tumours able to express ASMA (e.g. equine
Vimentin
Leiomyoma/sarcoma
Melanoma PNL-2
Equine sarcoid GIST ASMA MCT C-kit
Haemangioma / sarcoma Lymphangioma / sarcoma Factor VIII
FIGURE 1 Schematic drawing of main equine tumours (black characters) and immunohistochemical markers (white characters on blue background). Continuous line indicates diffuse positive labelling, while the dashed line indicates variable positive labelling. ASMA, alpha smooth muscular actin; GIST, gastrointestinal stromal tumour; MCT, mast cell tumour; Pan- CK, pan- cytokeratin; SCC, squamous cell carcinoma.
S-100
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76
