The art of identification of extravillous trophoblast

Immunohistochemical staining with specific markers for the respective cell type facilitates tracking and identification of cells such as extravillous trophoblast in the uterine wall. Cytokeratin has been recommended as a marker for all kinds of trophoblasts and is commonly used as a marker to identify interstitial as well as endovascular trophoblast. With immunohistochemical double staining of specimens of first trimester placental bed we show that staining with anti-cytokeratin alone is not sufficient to track all routes of trophoblast invasion. Endovascular trophoblasts can be easily mixed up with endoglandular trophoblasts. Thus, additional application of specific markers for extravillous trophoblast such as anti-HLA-G is strongly recommended, ideally in combination with other markers in immunohistochemical or immunofluorescence double staining.