CD97 promotes angiogenesis in vivo. Subcutaneous tumors from MEKDD-parental, MEKDD-CD97/5EGF, and MEKDD-CD97/3EGF cells were generated and stained for endothelial cells as described in “Materials and methods.” (A) Representative fields of blood vessels stained with CD31 were photographed. Arrows indicate CD31-stained endothelial cells. Image acquisition was performed as described elsewhere.³⁰  (B) Five ×32 microscopic fields were photographed and blood vessels more than 50 μm were counted. The results represent the mean of 5 fields for each of 4 tumors plus or minus SEM; n = 20; P values shown were determined by an unpaired t test comparing each CD97-expressing cell line to the parental.