PDGF-BB expression increases vascularization of B16 tumors. (A)-(D): Mock-transfected B16 melanoma cells, lacking PDGF-BB expression (Mock) and PDGF-BB expressing B16 melanoma cells (BB) were subcutaneously injected on both sides of the midline of the lower dorsal abdomen of wild type (wt) or D849N-mutant mice (mut). Six tumors were analyzed for each experimental combination. When the B16 melanomas had reached 0.8 cm3, they were removed and analyzed for ratio of total vessel area/viable tumor (A), average vessel surface (B), number of vessels per high-power field (C) and numerical density of pericytes per perimeter of vessel (D). Asterisks indicate statistical significance (*, p < 0.05; **, p < 0.01; ***, p < 0.001; ****, p < 0.0001) by Student's t-test.