Morphological and chromosomal analysis. (A) Histological features of the human original tumor revealed invasive ductal carcinoma and blood pooling without a lining of endothelia. (B) Characteristic appearance of the tumor at the site of subcutaneous inoculation. (C,D) Microscopic analysis of WIBC-9 stained with hematoxylin–eosin (C) and Giemsa (D) revealed hypervascularity, blood pooling without a lining of EC and no central necrosis or fibrosis in the center of the tumor nest. (E) Transmission electron microscopy revealed the interface between tumor cells and erythrocytes. (F) Phase-contrast electron microscopy clearly visualized erythrocytes between tumor cells. Erythrocytes appeared black. (G,H) Vasculogenic mimicry surrounding tumor cells was positive for Flt-1 (G) and Tie-2 (H). (I) Karyotype analysis of WIBC-9 revealing aneuploidy and marked chromosomal abnormalities.