In vivo growth of FaDu cells co-injected with murine fibroblasts. FaDu tumor cells (4 × 105 cells) were injected transcervically into the oral cavity of SCID mice alone or in combination with WT fibroblasts (8 × 105), MMP-2 null, MMP-9 null or MT1-MMP fibroblasts (8 × 105 (data not shown) or 1.2 × 106 cells). Measurements of tumor growth were taken at 10 days by ultrasound examination and at 14 days by histological sectioning of the mandible-tongue complex in the coronal plane (bar is 1 mm in coronal sections or 100 μM in histology) (A). Greatest cross sectional tumor area measurements were compared (B) for both groups. C, percent tumor formation in the orthotopic SCID mouse model over the two week observation period was equal to the number of tumors formed divided by number of mice (one injection per mouse with least 10 mice were injected per group).