Microvascular patency is maintained within LLC tumors of plasminogen-deficient mice when the tumors develop within the dorsal subcutis. Representative transmission electron micrographs illustrating dorsal skin tumor vasculatures of control (A), Plg^– (B), Fib^– (C), and Plg^–/Fib^– (D) mice. Note that in contrast to tumors grown in the footpad, tumors within the dorsal subcutis had no evidence of microvascular thrombus formation, regardless of animal genotype. Viable tumor cells are highlighted with asterisks, and endothelium is indicated with arrows. Horizontal bars in each micrograph indicate 8 μm.