Histologic appearance of primary tumors in Plg^−/− and control mice. Hematoxylin/eosin stain (A through F ) and PECAM immunostain (G and H) of primary tumors 11 days after tumor inoculation. (A and B) Typical appearance of skin overlying the primary tumor in a Plg^−/− mouse (A) and a control mouse (B). Both tumors exhibit skin breakdown with surface accumulation of serum proteins, exudate, and dead cell debris (escar). The arrow indicates intact skin. Arrowheads indicate escar. The asterisk indicates tumor. Bar = 100 μm. (C and D) Tumor invasion of dermal muscle in a Plg^−/− mouse (C) and a control mouse (D). Both tumors display diffuse invasion with separation and destruction of myocytes. The arrow indicates intact muscle. Arrowheads indicate muscle invaded by tumor. Bar = 100 μm. (E and F ) High magnification micrographs of the tumor in a Plg^−/− mouse (E) and a control mouse (F ). The micrographs show similar cytologic features with dense cellularity and severe anaplasia characterized by variation in cell size and shape and numerous mitoses (arrowheads), with some being bizarre (asterisk). Capillaries and endothelial cells are frequent in each tumor (arrows). Bar = 22 μm. (G and H) Immunostain for endothelial cells (PECAM) confirms the presence of numerous vessels in both Plg^−/− mice (G) and control mice (H). Bar = 100 μm.