Fig. 1

U-CH11 and U-CH11R cells are clonally related. a Hematoxylin/eosin staining of the primary and the recurrent chordoma tissues and in vitro light microscopy of U-CH11 and U-CH11R. The physaliferous cell morphology is conserved. b Immunocytochemical staining of the chordoma markers brachyury, S100-protein, vimentin, pan-cytokeratin, epithelial membrane antigen (EMA), and Ki-67. c Mean in vitro population doubling times (±SD; n = 3) of U-CH11 and U-CH11R at different cell densities (**p < 0.01) d Overlay of the array comparative genomic hybridization ratio plots of U-CH11 (green) and U-CH11R (blue) showing a high concordance of alterations. e Hierarchical cluster analysis of U-CH11 and U-CH11R in comparison to 12 additional chordoma cell lines. Clustering was performed in a Euclidean distance measure and single linkage rule