Histopathological findings of HTR8/SVneo/HRASV12-derived tumors mimicking human choriocarcinoma. A: Tumor formation derived from HTR8/SVneo/HRASV12 cells by subcutaneous injection into a nude mouse (left). The tumors were hemorrhagic and centrally necrotic (right). B: A tumor stamp specimen visualized with Papanicolaou staining reveals a marked large cell with hyperstained nucleus. C: H&E staining of tumors derived from HTR8/SVneo/HRASV12 cells by subcutaneous injections. The characteristic two-cell pattern, consisting of multinucleated syncytiotrophoblasts (dotted arrow) and mononuclear cytotrophoblasts (arrow), is shown (left, ×200 magnification; right, ×600 magnification). D: Most of the tumor cells were GFP-positive and rarely contained tumor stroma or vessels (GFP immunohistochemistry, ×200 magnification). E: Viable tumor cells were located at the periphery of hemorrhagic foci (H&E staining, ×200 magnification). F: Immunohistochemistry revealed that tumors expressed HLA-G (left, ×600 magnification) and cytokeratin (right, ×600 magnification). G: Immunohistochemistry revealed that tumors expressed hCG (left, ×600 magnification), but not hPL (right, ×600 magnification). H: Tumor formation from intraperitoneally injected cells. I: Intraperitoneally injected cells also exhibited the characteristic two-cell pattern consisting of multinucleated syncytiotrophoblasts (dotted arrow) and mononuclear cytotrophoblasts (arrow) (left, ×200 magnification; right, ×600 magnification). J: Tumors generated from intraperitoneally injected cells invading the liver. K: H&E staining of the tumor depicted in J (left, ×200 magnification; right, ×600 magnification). L: Tumor development in the lung by intravenous injection of HTR8/SVneo/HRASV12 cells. M: H&E staining of cells from the tumor depicted in L (left, ×200 magnification; right, GFP immunohistochemistry, ×200 magnification).