AN ORTHOTOPIC FLOOR-OF-MOUTH CANCER MODEL ALLOWS QUANTIFICATION OF TUMOR INVASION

Objectives: To establish an orthotopic murine floor-of-mouth cancer mo del of the analysis of the role of proteases such as urokinase-type pl asminogen activator (u-PA) and the matrix metalloprotease MMP-9 (MMP-9 ) in in vivo invasion. Study Design: Randomized, prospective animal st udy. Methods: Two human squamous cell carcinoma cell lines, UM-SCC-1 a nd 022, were assayed via zymography for their in vitro secretion level s of u-PA and MMP-9. Both cell lines (5 x 10(6) cells) were injected i nto the cervical subcutaneous tissues of female athymic nude (nu/nu) m ice superficial to the mylohyoid muscle. Mice were sacrificed after 30 days, and tumor invasion characteristics were histologically compared . Additional mice were then inoculated with invasive UM-SCC-1 cells an d sacrificed 10, 30, and 40 days after inoculation to identify distinc t stages of invasion. Results: In vitro secretion levels of MMP-9 and activity of u-PA were higher in UM-SCC-1 cells than in 022 cells. In t he in vivo studies, tumors formed from 022 cells were found to be noni nvasive, whereas tumors derived from UM-SCC-1 cells progressed through distinct and readily identifiable histologic stages of invasion. Thes e stages included invasion of adjacent muscle layers (mylohyoid, genio hyoid, and genioglossus muscles) and of associated structures (blood v essels, bone, nerve, and regional lymph nodes). A staging system was d evised accordingly. Conclusion: We developed an in vivo quantitative c ancer invasion model that allows determination of the effect of the ex pression and activity levels of the proteases MMP-9 and u-PA. Tumor in vasion occurred in an orderly and stepwise fashion involving muscles a nd related vascular, nervous, and bony structures of the floor of the mouth and tongue. This orderly invasion allowed the development of a s taging system. We anticipate that this model will have wide applicabil ity in the study of in vivo tumor response to a variety of novel thera peutic approaches.